Linux 版 (精华区)
发信人: netiscpu (说不如做), 信区: Linux
标 题: [B] Red Hat Linux Unleashed (32)
发信站: 紫 丁 香 (Sat Jul 25 04:59:59 1998), 转信
Motif for Programmers
_________________________________________________________________
o Writing Motif Applications
o Naming Conventions
o Writing Your First Motif Application
o Compiling This Application
o The Widget Hierarchy
# Core
# XmPrimitive
# XmManager
o The Label Widget
o Strings in Motif Compound Strings
o The XmPushButton Widget Class
o The XmToggleButton Widget Class
o Convenience Functions
o The List Widget
o XmScrollBar
o Text Widgets
o XmBulletinBoard Widgets
o XmRowColumn Widgets
o XmForm Widgets
o Designing Layouts
o Menus
# Pop-Up Menus
# The Menu Bar
# The Options Menu
# Accelerators and Mnemonics
o Dialog Boxes
# Modes of a Dialog Box
o Events
# Expose Events
# Pointer Events
# Keyboard Events
# Window Crossing Events
# Event Masks
o Managing the Queue
# Work Procedures
# Using Timeouts
# Handling Other Sources
o The Graphics Context
o Drawing Lines, Points, Arcs, and Polygons
# Drawing a Line
# Drawing a Point
# Drawing an Arc
o Using Fonts and FontLists
o The X Color Model
o Pixmaps, Bitmaps, and Images
o Summary
_________________________________________________________________
32
Motif for Programmers
This chapter will cover the following topics:
* The basics of writing Motif applications for Linux
* Special naming conventions in Motif and X
* Writing and compiling your first Motif application
* Revisiting the widget hierarchy
* Using labels and strings in Motif
* Using various common widgets
* Designing layout
* Using menus
* Dialog boxes
* Event handling and other sources of input
* Colors in X
* Drawing lines, points, arcs, and polygons
A question you might be asking is "Why include a topic on a
development system that you have to pay for when just about everything
for Linux is free?" Well, if you want to develop any applications for
the Common Desktop Environment (CDE), you should know how to program
Motif applications. Linux is a mature enough system to enable you this
luxury of building portable applications. (Plus, the $150 or so (U.S.)
you pay for the Motif license will well pay for itself if you can do
the work at home on your Linux system rather than commuting!)
Writing Motif Applications
This chapter introduces you to writing Motif applications. The
information here will not be limited to writing applications for Linux
alone, because the concepts in this chapter can be applied to other
UNIX systems as well.
In programming Motif applications, you have to get used to programming
in an event-driven environment. A typical C application runs from
start to finish at its own pace. When it needs information, the
application looks for this information from a source such as a file or
the keyboard and (almost always) gets the information as soon as it
asks for it. If the information is not available when the application
asks for it, the application either waits for it or displays an error
message. Also, the order of the incoming data is important for such
applications; pieces of data that are out of sequence may cause the
application to behave strangely.
In the case of event-driven programming, an application must wait for
events on an input queue. The queue orders all incoming events in the
order they are received. The first message to come in from one end of
a queue is the first one to leave the queue. (Such queues are often
called FIFOs, for First In, First Out.) An event can be anything from
a mouse click, key button, or other event such as a timeout
notification.
Because events can come in at any time, and in no predefined order,
they are referred to as asynchronous events. That is, the order and
time of arrival of each event is not deterministic. The application
must wait for an event to occur and then proceed based on that event.
Thus the term event-driven programming.
In the case of X Window, each X Window application has one input queue
for all of its incoming events. The application must wait for events
on this input queue. Similarly, a server waits for an event from a
client and then responds based on the type of event received. This
event handling and other aspects of X programming are handled by a
toolkit called XtIntrinsics, or Xt for short.
In Xt, an application will typically run in a loop forever. This loop
is called an event loop. An application enters the loop by calling a
function XtAppMainLoop(). While in this event loop, an application
will always wait for an event, When the application receives an event,
the application handles the event itself or almost always "dispatches"
the event to a window or Widget.
A Widget registers functions that it wants called when a type of event
is received. This function is called a callback function. In most
cases, a callback function is independent of the entire application.
For example, some Widgets will redraw themselves when a pointer button
is clicked in their display area. In this case, they would register a
redraw callback function on a button click.
Xt also supports actions, which enable applications to register a
function with Xt. An action is called when one or more sequences of
specific event types are received. For example, pressing Ctrl-X would
call the exit function. The mapping of the action to an event is
handled via a translation table within Xt. Functions that handle
specific events are referred to as event handlers.
Look at Figure 32.1 to see how the toolkit exists with Motif. As you
can see from the connections in the figure, an application can get to
the core Xlib functions through three means: via Motif, via the Xt
library, or directly. This flexible hierarchy gives you many options
when developing Motif applications because you are at liberty to take
full advantage of all functions in all three libraries.
Figure 32.1. The toolkit hierarchy for X, Xt, Motif.
Naming Conventions
By default, most Xlib functions begin with the letter X, but you
should not always rely on this being true for all functions. Several
macros and functions in the X Window system do not begin with X. For
example, BlackColor and WhiteColor are not macros. In general, though,
if a name in Xlib begins with X, it's probably a function. If a name
begins with a capital letter (A through Z), it's a macro.
With Xt, the naming conventions get better, but only slightly. In Xt,
macros are not differentiated from functions in any way.
______________________________________________________________
NOTE: Do not rely on the name of a toolkit function to give you
information about whether it's a macro. Read the manual to be
absolutely sure.
______________________________________________________________
In Motif, almost all declarations begin with Xm. Therefore, XmC refers
to a class, XmR refers to a resource, XmN refers to a name, and XtN
refers to Xt resources used by Motif. Declarations ending with the
words WidgetClass define the base class for a type of Widget. A few
conventions to remember about parameters for most Xlib functions are
* Width always to the left of height
* X always to the left of y
* Source always to the left of destination
* Display usually is the first parameter
With practice, you will be able to identify the type of parameters to
pass and which toolkit a function belongs to, and be able to make some
educated guesses as to what parameters an unknown function might
expect.
Writing Your First Motif Application
Let's look at the basic format for a Motif application, shown in
Listing 32.1. (I added line numbers for your benefit.) I will discuss
this application in detail. You will build other Motif applications
based on the structure in this particular application as you progress
through this chapter.
______________________________________________________________
NOTE: The line numbers are for reference only.
______________________________________________________________
Listing 32.1. A sample Motif application.
1 /*
2 ** This is a typical Motif application with one button that
3 ** exits it.
4 */
5 #include <X11/Intrinsic.h>
6 #include <Xm/Xm.h>
7 #include <Xm/Form.h>
8 #include <Xm/PushB.h>
9 void bye(Widget w, XtPointer clientdata, XtPointer calldata);
10 int main(int argc, char **argv)
11 {
12 Widget top;
13 XtAppContext app;
14 Widget aForm;
15 Widget aButton;
16 Arg args[5];
17 /**
18 *** Initialize the toolkit.
19 **/
20 top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
21 argv, NULL, args, 0);
22 /**
23 *** Create a Form on this top level Widget. This is a nice Widget
24 *** to place other Widgets on top of.
25 **/
26 aForm = XtVaCreateManagedWidget("Form1",
27 xmFormWidgetClass, top,
28 XmNheight,90,
29 XmNwidth,200,
30 NULL);
31 /**
32 *** Add a button on the form you just created. Note how this Button
33 *** Widget is connected to the form that it resides on. Only
34 *** left, right, and bottom edges are attached to the form. The
35 *** top edge of the button is not connected to the form.
36 **/
37 aButton = XtVaCreateManagedWidget("Push to Exit",
38 xmPushButtonWidgetClass, aForm,
39 XmNheight,20,
40 XmNleftAttachment,XmATTACH_FORM,
41 XmNrightAttachment,XmATTACH_FORM,
42 XmNbottomAttachment,XmATTACH_FORM,
43 NULL);
44 /**
45 *** Call the function "bye" when the PushButton receives
46 *** an activate message; i.e. when the pointer is moved to
47 *** the button and Button1 is pressed and released.
48 **/
49 XtAddCallback( aButton, XmNactivateCallback,
50 bye, (XtPointer) NULL);
51 XtRealizeWidget(top);
52 XtAppMainLoop(app);
53 return(0);
54 }
55 void bye(Widget w, XtPointer clientdata, XtPointer calldata)
56 {
57 exit(0);
58 }
The listing shows an application in which a button attaches itself to
the bottom of a form. See Figure 32.2.
Figure 32.2. The output of l32_1.c.
No matter how you resize the window, the button will always be on the
bottom. The application does the following things in the order listed:
1. Initializes the toolkit to get a shell Widget.
2. Makes a Form Widget.
3. Manages all Widgets as they are created.
4. Makes the Button Widget on top of the Form Widget.
5. Attaches a callback function to the button.
6. Realizes the Widget (that is, makes the hierarchy visible).
7. Goes into its event loop.
Let's look at the application in more detail. The include files in the
beginning of the listing are required for most applications. Notably,
the two files shown in lines 5 and 6 are required for just about any
Motif application you'll ever write.
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
These two lines declare the definitions for XtIntrinsics and Motif,
respectively. In some systems, you may not require the first
inclusion, but it's harmless to put it in there because multiple
inclusions of Intrinsic.h are permitted. In addition, each Motif
Widget requires its own header file. In Listing 32.1, the Widgets Form
and PushButton are included via statements in lines 7 and 8:
#include <Xm/Form.h>
#include <Xm/PushB.h>
The variables in the program are declared in lines 12 through 16:
Widget top;
XtAppContext app;
Widget aForm;
Widget aButton;
int n;
The top, aForm, and aButton represent Widgets. Even though their
functions are different, they can all be referred to as Widgets.
The XtAppContext type is an opaque type, which means that a Motif
programmer does not have to be concerned about how the type is set up.
Widgets are opaque types as well; only the items that are required for
the programmer are visible.
The first executable line of the program calls the XtAppInitialize()
function (in line 20) to initialize the Xt toolkit and create an
application shell and context for the rest of the application. This
value is returned to the Widget top (for top-level shell). This Widget
will provide the interface between the window manager and the rest of
the Widgets in this application.
The application then creates a Form Widget on this top-level Widget. A
form widget is used to place other Widgets on top of itself. It is a
manager widget because it "manages" other Widgets.
There are two steps required for displaying a Widget: First you have
to manage (with XtVaCreateManagedWidget) it and then you have to
realize (with RealizeWidget) it.
Managing a Widget enables it to be visible. If a Widget is unmanaged,
it will never be visible. By managing a Widget, the program gives the
viewing control over to the windowing system to enable it to display
it. Any child Widgets remain invisible, even if they are managed, if
the parent Widget is unmanaged.
Realizing a Widget actually creates all the subwindows under an
application and displays them. Normally only the top-level Widget is
realized after all the Widgets are managed. This call will realize all
the children of this Widget.
Note that realizing a Widget takes time. A typical program will manage
all the Widgets except the topmost one. This way the application will
only have to realize the topmost Widget when the entire tree has to
display only the topmost parent. You have to realize a Widget at least
once, but you can manage and "unmanage" Widgets as you want to display
or hide them.
You can always create and manage a Widget to call XtCreate and
XtManageChild in two separate calls. However, the samples in this
chapter will use a single call to create and manage a Widget:
XtVaCreateManagedWidget.
Note the parameters in this call to create the Form Widget shown in
lines 26 through 30:
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,90,
XmNwidth,200,
NULL);
The first parameter is the name of the new Widget. The second
parameter describes the class of the Widget being created. Recall that
this is simply the Widget name sandwiched between xm and WidgetClass.
So, in this case, it is xmFormWidgetClass. Note the lowercase x for
the class pointer. This class pointer is declared in the header files
included at the beginning of the file, Form.h.
______________________________________________________________
NOTE: As another example, the class pointer for a Label would be
called xmLabelWidgetClass and would require the Label.h file. Motif
programmers have to be especially wary of the case of all
variables.
______________________________________________________________
The next argument is the parent Widget of this new Widget. In this
case, top is the parent of Form1. The top Widget is returned from the
call to XtAppInitialize.
The remaining arguments specify the parameters of this Widget. In this
case you are setting the width and height of the Widget. This list is
terminated by a NULL parameter.
After the form is created, a button is placed on top of it. A Form
Widget facilitates placement of other Widgets on top of it. In this
application you will cause the button to "attach" itself to the bottom
of the form. The following three lines (40—42) attach themselves
to the form:
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_FORM,
The class of this button is included in the PushB.h file and is called
xmPushButtonWidgetClass. The name of this Widget is also the string
that is displayed on the face of the button. Note that the parent of
this button is the aForm Widget. The hierarchy is as follows:
top -> is the parent of aForm -> is the parent of -> aButton.
The next step is to add a callback function when the button is
pressed. This is done with the call to XtAddCallback, as shown in the
following:
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
Here are the parameters for this call:
* aButton is the PushButton Widget.
* XmNactivateCallback is the action that will trigger a call to this
function.
* bye is the name of the function that will be called when the
action is triggered. (You should declare this function before
making this function call, or you will get a compiler error.)
* NULL is a pointer. This pointer could point to some structure
meaningful to function bye.
This will register the callback function bye for the Widget. Now the
topmost Widget, top, is realized. This causes all managed Widgets
below top to be realized. The application then goes into a loop that
processes all incoming events.
The bye function of this program simply exits the application.
Compiling This Application
Now comes the tough part of compiling this application into a working
application. You will use the gcc compiler that comes with Linux for
this purpose.
First, check the location of the libraries in your system. Check the
/usr/lib/X11 directory for the following libraries: libXm.a, libXt.a,
and libX11.a. If possible, use the shared library versions of these
libraries with .so extensions followed by some numbers. The advantage
of using shared libraries is a smaller Motif application; a typical
application like the one you've been working on can be up to 1MB in
size because of Motif's overhead.
The disadvantage of shared libraries is that your end user may not
have the correct version of the library in his path. This does annoy
some end users, especially if no fast method of acquiring this
resource is available. Also, shipping a shared library with your
application may cause you to pay some licensing fees to the original
library vendor. From a programmer's perspective, shared libraries are
sometimes impossible to use with your debugger. Of course, if your
debugger supports them, use it. Check your compiler documentation. In
most cases, if you intend to use shared libraries, use the static
versions to do your debugging and testing, and then compile the shared
version. Always check your vendor's licensing agreement for details on
how to ship shared libraries.
The application can be compiled with this command:
gcc l32_1.c -o list1 -lXm -lXt -lX11 -I/usr/x11/include -L/usr/x11/lib
The program can be run from a command line if you create a script
file:
$ cat mk
gcc $1.c -o $1 -lXm -lXt -lX11 -I/usr/x11/include -L/usr/x11/lib
and pass it just the filename without the extension. The best way is
to create a makefile, but this script file will work with the examples
in this text. So, to compile l32_1.c, you would use the script as
follows:
$ mk l32_1
You should see the output in Figure 32.2 on your screen. Your
application is the one with l32_1 in its frame.
The Widget Hierarchy
The Motif Widget set is a hierarchy of Widget types. (See Figure
32.3.) Any resources provided by a Widget are inherited by all its
derived classes. Consider the three most important base classes: Core,
XmPrimitive, and XmManager.
Figure 32.3. The partial Motif hierarchy.
Core
The Core Widget class provides the basis for all classes. It provides
at least the following resources for all Widgets:
XmNx,XmNy: A Widget's position on the display.
XmNheight, XmNwidth: A Widget's size.
XmNborderWidth: Set to 1 by default.
XmNsensitive: A Boolean resource that specifies whether this
Widget can receive input.
XmNcolorMap: The default color map.
XmNbackground: The background color.
Check the Motif Programmer's reference manual for a complete listing.
XmPrimitive
The XmPrimitive Widget class inherits all the resources from Core and
adds more functionality.
XmNforeground: The foreground color.
XmNhighlightOnEnter: Changes color when the pointer is within a
displayed area of Widget.
XmNhighlightThickness: If XmNhighlightOnEnter is TRUE, changes
the border to this thickness.
XmNhighlightColor: The color it changes to when highlighted.
XmNshadowThickness: This is the thickness to show the
pseudo-three-dimensional look for which Motif is famous. The
default value is 2.
XmNtopShadowColor and XmNbottomShadowColor: Sets the color for
top and bottom lines around a Widget.
XmNuserData: A pointer available for the programmer's use.
The XmPrimitive Widget also provides the XmNdestroyCallback resource.
This can be set to a function that would do clean-up when a Widget is
destroyed. In Motif 1.2.x or later, the XmPrimitive class also
provides a XmNhelpCallback that is called when the F1 key is pressed
in the Widget's window. This is to allow specific help information for
a button, for example.
XmManager
The XmManager class provides support for all Motif Widgets that
contain other Widgets. This is never used directly in an application,
and it works in a manner similar to the XmPrimitive class. It provides
the following resources:
XmNforeground: The color of the pixels in the foreground.
XmNshadowThickness: For the three-dimensional effect.
XmNtopShadowColor: For the three-dimensional effect. This is
automatically defaulted to a color derived from the
background color. This color is used on the left and top
borders of a Widget.
XmNbottomShadowColor: For the three-dimensional effect. This is
automatically defaulted to a color derived from the
background color. This color is used on the right and bottom
borders of a Widget.
XmNuserData: For storing user data. Could be used as a void
pointer.
The Label Widget
The Label Widget is used to display strings or pixmaps. Include the
Xm/Label.h file in your source file before using this Widget. Some of
the resources for this Widget include the following:
XmNalignment: Determines the alignment of the text in this
Widget. The acceptable values are XmALIGNNMENT_END,
XmALIGNMENT_CENTER, and XmALIGNEMENT_BEGIN for right, center,
and left justification, respectively.
XmNrecomputeSize: A Boolean resource. If set to TRUE, the Widget
will resize should the size of the string or pixmap change
dynamically. This is the default. If set to FALSE, the Widget
will not attempt to resize itself.
XmNlabelType: The default value of this type is XmSTRING to show
strings. However, it can also be set to XmPIXMAP when
displaying a pixmap specified in the XmNpixmap resource.
XmNlabelPixmap: This is used to specify which pixmap to use when
the XmNlabelType is set to XmPIXMAP.
XmNlabelString: This is used to specify which XmString compound
string to use for the label. This defaults to the name of the
label. See the section, "Strings in Motif: Compound Strings."
To get acquainted with left and right justification on a label, see
Listing 32.2. The listing also shows how the resources can be set to
change Widget parameters programmatically and via the .Xresource
files.
Listing 32.2. How to use a Label Widget.
/*
** This application shows how to use a Label Widget.
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/Label.h> /** <---- for the label **/
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget aForm;
Widget aLabel; /** <---- for the label ***/
Widget aButton;
Arg args[5];
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,90,
XmNwidth,200,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
/**
*** Now let's create the label for us.
*** The alignment is set to right-justify the label.
*** Note how the label is attached to the parent form.
**/
aLabel = XtVaCreateManagedWidget("This is a right justified Label",
xmLabelWidgetClass, aForm,
XmNalignment, XmALIGNMENT_END,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
NULL);
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
Output is shown in Figure 32.4.
Figure 32.4. Using the Label Widget.
Avoid using the \n in the label name. If you have to create a
multistring Widget, use the XmStringCreate calls to create a compound
string (see the next section). Another way to set the string is by
specifying it in the resource file and then merging the resources.
The listing shows the Label to be right-justified. You could easily
center the string horizontally by not specifying the alignment at all
and letting it default to the center value. Alternatively, try setting
the alignment parameter to XmALIGNMENT_BEGINNING for a left-justified
label.
Strings in Motif Compound Strings
A compound string is Motif's way of representing a string. In a
typical C program, a NULL-terminated string is enough to specify a
string. In Motif, a string is also defined by the character set it
uses. Strings in Motif are referred to as compound strings and are
kept in opaque data structures called XmString.
In order to get a compound string from a regular C string, use this
function call:
XmString XmStringCreate( char *text, char *tag);
This function will return an equivalent compound string given a
pointer to a NULL-terminated C string and a tag. The tag specifies
which fontlist to use and is defaulted to XmFONTLIST_DEFAULT_TAG.
New lines in C strings have to be handled by special separators in
Motif. So to create a string and preserve the newlines, use the call
XmString XmStringCreateLtoR( char *text, char *tag);
The compound strings have to be created and destroyed just like any
other object. They persist long after that function call that created
them returns. Therefore, it's a good idea to free all locally used
XmStrings in a function before returning, or else all references to
the strings will be lost. The definition of a call to free XmString
resources is
XmStringFree( XmString s);
You can run similar operations on strings as you would in a C program,
except that these string operations are called by different names. Use
the function
Boolean XmStringByteCompare( XmString s1, XmString s2);
for a strict byte-for-byte comparison, and for a just the text
comparison, use
Boolean XmStringCompare( XmString s1, XmString s2);
To check if a string is empty, use
Boolean XmStringEmpty( XmString s1);
To string two strings together, use
XmString XmStringConcat( XmString s1, XmString s2);
XmString Concat() creates a new string by concatenating s2 to s1 and
returns it. This returned string has to be freed just like s1 and s2.
If you want to use sprintf, use it on a temporary buffer and then
create a new string. For example:
char str[32];
XmString xms;
......
sprintf(str," pi = %lf, Area = %lf", PI, TWOPI*r);
xms = XmStringCreateLtoR( str, XmFONTLIST_DEFAULT_TAG);
......
n = 0;
XtSetArg(arg[n],XmNlabelString,xms); n++;
XtSetValues(someLabel, arg, n);
XmStringFree(xms);
If a string value becomes corrupted without your performing any direct
actions on it, check to see whether the Widget is not making a copy
for its use of the passed XmString. Sometimes a Widget might be
keeping only a pointer to the XmString. If that string were freed, the
Widget might wind up pointing to bad data.
One good way to check is to set an XmString resource, then use the
XtGetValues function to get the same resource from the Widget. If the
values of the XmStrings are the same, the Widget is not making a copy
for itself. If they are not the same, it is safe to free the original
because the Widget is making a local copy. The default course of
action is to assume that a Widget makes a copy of such resources for
itself.
A similar test could be used to determine whether a Widget returns a
copy of its resource or to a pointer to it. Use the same listing shown
previously, but this time use a getValue to get the same resource
twice. Then do the comparison to see whether the address for the
original string matches the address of the returned value from
getValue(): If the values match, the Widget keeps a pointer. If the
values do not match, the Widget keeps an internal copy.
/**
*** This is a sample partial listing of how to check if the
*** data returned on an XtGetValues and an XtSetValues
*** call is a copy or a reference.
***/
#include "Xm/Text.h"
..
Widget w;
XmString x1, x2, x3;
x3 = XmStringCreateLtoR("test", XmFONTLIST_DEFAULT_TAG);
XmTextSetString(w,x3);
...
x1 = XmTextGetString(w);
x2 = XmTextGetString(w);
XtWarning(" Checking SetValues");
if (x1 != x3)
XtWarning("Widget keeps a copy ! Free original!");
else
XtWarning("Widget does not keep a copy! Do NOT free original");
XtWarning(" Checking GetValues");
if (x1 == x2)
XtWarning("Widget returns a copy! Do NOT free");
else
XtWarning("Widget does not return a copy! You should free it ");
The XtWarning() message is especially useful for debugging the
progress of programs. The message is relayed to the stderr of the
invoking application. If this is an xterm, you will see an error
message on that terminal window. If no stderr is available for the
invoke mechanism, the message is lost.
______________________________________________________________
NOTE: The XtSetArg macro is defined as
<LC2>#define XtSetArg(arg,n,d) \
((void)((arg).name = (n).(arg).value = (XtArgVal)))
Do not use XtSetArg(arg[n++]_ as this will increment n twice.
______________________________________________________________
The XmPushButton Widget Class
The XmPushButton is perhaps the most heavily used Widget in Motif.
Listings 32.1 and 32.2 show the basic usage for PushButton. When a
button is pressed in the PushButton area, the button goes into an
armed state (a state between not pressed and going to pressed). The
color of the button changes to reflect this state, and you can set
this color by using XmNarmColor. This color is shown when the
XmNfillOnArm resource is set to TRUE.
______________________________________________________________
NOTE: If the armColor for a PushButton does not seem to be working,
try setting the XmNfillOnArm resource to TRUE.
______________________________________________________________
The callback functions for a PushButton are the following:
XmNarmCallback: Called when a PushButton is armed.
XmNactivateCallback: Called when a button is released in the
Widgets area while the Widget is armed. This is not invoked
if the pointer is outside the Widget when the button is
released.
XmNdisarmCallback: Called when a button is released with the
pointer outside the Widget area while the Widget was armed.
______________________________________________________________
NOTE: If a callback has more than one function registered for a
Widget, all of the functions will be called, but not necessarily in
the order they were registered. Also, do not rely on the same order
being preserved on other systems. If you want more than one
function performed during a callback, sandwich them in one function
call.
______________________________________________________________
In Listing 32.2, you saw how a callback function was added to a
PushButton with the XtAddCallback function. The same method can be
used to call other functions for other actions such as the
XmNdisarmCallback.
The XmToggleButton Widget Class
This class is a subclass of the XmLabel Widget class. You can have two
types of buttons: one of many or n of many. When using one of many,
the user can make only one selection from many items. (See Figure
32.5.) When using n of many, the user can select many options. (See
Figure 32.6.) Note the way the buttons are drawn, with one of many
shown as diamonds and n of many shown as boxes.
Figure 32.5. One of many toggle buttons.
Figure 32.6. Using n of many toggle buttons.
The resources for this Widget include the following:
XmNindicatorType: Determines the style. Can be set to XmN_OF_MANY
or XmONE_OF_MANY (the default).
XmNspacing: The number of pixels between the button and its
label.
XmNfillOnSelect: The color of the button changes to reflect a set
when the XmNfillOnArm resource is set to TRUE.
XmNfillColor: The color to show when set.
XmNset: A Boolean resource indicating whether the button is set
or not. If this resource is set from a program, the button
will automatically reflect the change.
It's easier to use the convenience functions:
XmToggleButtonGetState(Widget w)
to get the Boolean state for a Widget, and to use
XmToggleButtonSetState(Widget w, Boolean b)
to set the value for a ToggleButton Widget.
Similar to the PushButton class, the ToggleButton class has three
callbacks:
XmNarmCallback: Called when the ToggleButton is armed.
XmNvalueChangedCallback: Called when a button is released in the
Widgets area while the Widget is armed. This is not invoked
if the pointer is outside the Widget when the button is
released.
XmNdisarmCallback: Called when a button is released with the
pointer outside the Widget area while the Widget was armed.
For the callbacks, the data passed into the Callback function is a
structure of type:
typedef struct {
int reason;
Xevent *event;
int set;
} XmToggleButtonCallbackStruct;
The reason for the callback is one of the following events: XmCR_ARM,
XmCR_DISARM, or XmCR_ACTIVATE. The event is a pointer to XEvent, which
caused this callback. The set value is 0 if the item is not set, or
nonzero if set. Look at Listing 32.3, which shows the use of
ToggleButton. The ToggleButtons are arranged in one column via the
RowColumn Widget, discussed later in this chapter.
Listing 32.3. Using ToggleButton in Motif.
/*
** This is a typical Motif application that demonstrates the use of
** a ToggleButton Widget(s) stored on a RowColumn Widget.
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/ToggleB.h>
#include <Xm/RowColumn.h>
#include <Xm/PushB.h>
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
#define MAX_BTNS 4
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget aForm;
Widget aButton;
Widget aRowCol;
char str[32];
Widget aToggle[MAX_BTNS];
Arg args[5];
int i;
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,150,
XmNwidth,100,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
#define DO_RADIO
/**
*** A quick intro to the hierarchy in Motif.
*** Let's create a RowColumn Widget to place all ToggleButtons.
*** Note how the RowColumn button attaches itself to
*** the top of the button.
**/
aRowCol = XtVaCreateManagedWidget("rowcol",
xmRowColumnWidgetClass, aForm,
#ifdef DO_RADIO
XmNradioBehavior, TRUE,
XmNradioAlwaysOne, TRUE,
#endif
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_WIDGET,
NULL);
/**
*** Make ToggleButtons on this form called RowCol. Attach them all to the
*** RowColumn Widget on top of the form.
***
*** Note the radioBehavior setting
**/
for (i=0; i< MAX_BTNS; i++)
{
sprintf(str,"Button %d",i);
aToggle[i] = XtVaCreateManagedWidget(str,
xmToggleButtonWidgetClass, aRowCol,
XmNradioBehavior, TRUE,
NULL);
}
XmToggleButtonSetState(aToggle[0],TRUE, FALSE);
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
See Figure 32.6, shown previously, for the output of this listing with
the #define DO_RADIO line commented out. By defining the DO_RADIO
label, you can make this into a Radio Button application. That is,
only one of the buttons can be selected at one time. See Figure 32.5,
shown previously, for the radio behavior of these buttons.
Convenience Functions
Usually the way to set resources for a Widget is at the time of the
Widget's creation. This is done either with the
XtVaCreateManagedWidget call or with the XmCreateYYY call, where YYY
is the name of the Widget you are creating.
This test uses the variable argument call to create and manage
Widgets. I do it simply because it's easier for me to see what
resources I am setting and create them all in one function call. You
might have a personal preference to do it in two steps. Either way is
fine. Keep in mind, though, that if you do use the XmCreateYYY call,
you have to set the resource settings in a list of resource sets.
Listing 32.4 is an example of creating a Label Widget. This is a
function that creates a Label Widget on a Widget given the string x.
Listing 32.4. Sample convenience function for creating a Label on a
form.
/**
*** This is a sample convenience function to create a label
*** Widget on a parent. The string must be a compound string.
**/
Widget makeLabel( Widget onThis, XmString x)
{
Widget lbl;
Cardinal n;
Arg arg[5];
n = 0;
XtSetArg(arg[n], XmNalignment, XmALIGNMENT_BEGIN); n++;
XtSetArg(arg[n], XmNlabelString, x); n++;
lbl = XmCreateLabel("A Label", onThis, arg, n);
XtManageChild(lbl);
return(lbl);
}
Or you could use the variable argument lists in creating this Label,
as shown in Listing 32.5.
Listing 32.5. Creating a label.
/**
*** Another way of making a label on a parent.
**/
Widget makeLabel( Widget onThis, XmString x)
{
Widget lbl;
lbl = XmCreateManagedWidget("A Label",
xmLabelWidgetClass, onThis,
XmNalignment, XmALIGNMENT_BEGIN,
XmNlabelString, x,
NULL);
return(lbl);
}
In either case, it's your judgment call as to which one to use. The
variable list method of creating is a bit easier to read and maintain.
But what about setting values after a Widget has been created? This
would be done via a call to XtSetValue with a list and count of
resource settings. For example, to change the alignment and text of a
Label, you would use
n = 0;
XtSetArg(arg[n], XmNalignment, XmALIGNMENT_BEGIN); n++;
XtSetArg(arg[n], XmNlabelString, x); n++;
XtSetValues(lbl,arg,n);
Similarly, to get the values for a Widget, you would use XtGetValues:
Cardinal n; /* usually an integer or short... use Cardinal to be safe */
int align;
XmString x;
...
n = 0;
XtSetArg(arg[n], XmNalignment, &align); n++;
XtSetArg(arg[n], XmNlabelString, &x); n++;
XtGetValues(lbl,arg,n);
In the case of other Widgets, let's use the Text Widget. This setting
scheme is hard to read, quite clumsy, and prone to typos. For example,
when you get a string for a Text Widget, should you use x or address
of x?
For this reason, Motif provides convenience functions. For example, in
the ToggleButton Widget class, rather than using the combination of
XtSetValue and XtSetArg calls to get the state, you would use one
call, XmToggleButtonGetState(Widget w), to get the state. These
functions are valuable code savers when writing complex applications.
In fact, you should write similar convenience functions whenever you
can't find one that suits your needs.
The List Widget
This displays a list of items from which the user selects. The list is
created from a list of compound strings. Users can select either one
or many items from this list. The resources for this Widget include
the following:
XmNitemCount: Determines the number of items in the list.
XmNitems: An array of compound strings. Each entry corresponds to
an item in the list. Note that a List Widget makes a copy for
all items in its list when using XtSetValues; however, it
returns a pointer to its internal structure when returning
values to a XtGetValues call. Therefore, do not free this
pointer from XtGetValues.
XmNselectedItemCount: The number of items currently selected.
XmNselectedItems: The list of selected items.
XmNvisibleItemCount: The number of items to display at one time.
XmNselectionPolicy: Used to set single or multiple selection
capability. If set to XmSINGLE_SELECT, the user will be able
to only select one item. Each selection will invoke the
XmNsingleSelectionCallback. Selecting one item will deselect
a previously selected item. If set to XmEXTENDED_SELECT, the
user will be able to select a block of contiguous items in a
list. Selecting a new item or more will deselect another
previously selected item and will invoke the
XmNmultipleSelection callback. If set to XmMULTIPLE_SELECT,
the user will be able to select multiple items in any order.
Selecting one item will not deselect another previously
selected item but will invoke the XmNmultipleSelection
callback. If set to XmBROWSE_SELECT, the user can move the
pointer (with the button pressed) across all the selections,
but only one item will be selected. Unlike the
XmSINGLE_SELECT setting, the user does not have to press and
release the button on an item to select it. The
XmbrowseSelectionCallback will be invoked when the button is
finally released on the last item browsed.
It is easier to create the List Widget with a call to
XmCreateScrolledList() because this will automatically create a
scrolled window for you. However, scrolled windows may prove to be
slow when compared to XtSetValues() calls. If you feel that speed is
important, consider using XtSetValues(). You should create the list
for the first time by using XtSetValues.
The following convenience functions will make working with List
Widgets easier.
XmListAddItem(Widget w, XmString x, int pos)
This will add the compound string x to the List Widget w at
the one relative position pos. If pos is 0, the item is added
to the back of the list. This function is very slow, so do
not use it to create a newlist, because it rearranges the
entire list before returning.
XmListAddItems(Widget w, XmString *x, int count, int pos);
This will add the array of compound strings x of size count
to the List Widget w from the position pos. If pos is 0, the
item is added to the back of the list. This function is slow,
too, so do not use it to create a newlist.
XmDeleteAllItems(Widget w)
This will delete all the items in a list. It's better to
write a convenience function to do
n = 0; XtSetArg(arg[n], XmNitems, NULL); n++;
XtSetArg(arg[n], XmNitemCount, 0); n++;
XtSetValues(mylist,arg,n);
XmDeleteItem(Widget w, XmString x)
Deletes the item x from the list. This is a slow function.
XmDeleteItems(Widget w, XmString *x, int count)
Deletes all the count items in x from the list. This is an
even slower function. You might be better off installing a
new list.
XmListSelectItem(Widget w, XmString x, Boolean Notify)
Programmatically selects x in the list. If Notify is True,
the appropriate callback function is also invoked.
XmListDeselectItem(Widget w, XmString x)
Programmatically deselects x in the list.
XmListPos( Widget w, XmString x)
Returns the position of x in the list. Returns 0 if not
found.
Let's use the List Widget for a sample application. See Listing 32.6.
Listing 32.6. Using List Widgets.
/*
** This is a typical Motif application for using a list Widget
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/List.h> /*** for the list Widget ***/
#include <Xm/ScrolledW.h> /*** for the scrolled window Widget ***/
/*** Some items for the list ***/
#define NUMITEMS 8
char *groceries[NUMITEMS] = {
"milk",
"eggs",
"bread",
"pasta",
"cd-rom", /** I don't go out often!**/
"bananas",
"yogurt",
"oranges",
};
/* For the list Widget, we need compound strings */
XmString xarray[NUMITEMS];
#define USE_SCROLL
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget aForm;
Widget aList;
Widget aButton;
Arg args[15];
int i;
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,90,
XmNwidth,200,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
/**
*** Now create a list of items for this Widget.
**/
for (i=0; i < NUMITEMS; i++)
xarray[i] = XmStringCreateLtoR(groceries[i],
XmSTRING_DEFAULT_CHARSET);
#ifndef USE_SCROLL
/**
*** Then create the list Widget itself. Note this will not
*** put up a scroll bar for you.
**/
aList = XtVaCreateManagedWidget("Push to Exit",
xmListWidgetClass, aForm,
XmNitemCount, NUMITEMS,
XmNitems, xarray,
XmNvisibleItemCount, 4,
XmNscrollBarDisplayPolicy, XmAS_NEEDED,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_WIDGET,
XmNbottomWidget,aButton,
NULL);
#else
/**
*** Alternatively, use the scrolled window with the following code:
**/
i = 0;
XtSetArg(args[i], XmNitemCount, NUMITEMS); i++;
XtSetArg(args[i], XmNitems, xarray); i++;
XtSetArg(args[i], XmNvisibleItemCount, 4); i++;
XtSetArg(args[i], XmNscrollBarDisplayPolicy, XmAS_NEEDED); i++;
XtSetArg(args[i], XmNleftAttachment,XmATTACH_FORM); i++;
XtSetArg(args[i], XmNrightAttachment,XmATTACH_FORM); i++;
XtSetArg(args[i], XmNtopAttachment,XmATTACH_FORM); i++;
XtSetArg(args[i], XmNbottomAttachment,XmATTACH_WIDGET); i++;
XtSetArg(args[i], XmNbottomWidget,aButton); i++;
aList = XmCreateScrolledList(aForm,"groceryList",args,i);
XtManageChild(aList);
#endif
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
The output is shown in Figure 32.7.
Figure 32.7. Using the List Widget.
XmScrollBar
The ScrollBar Widget enables the user to select a value from a range.
Its resources include the following:
XmNvalue: The value representing the location of the slider.
XmNminimum and XmNmaximum: The range of values for the slider.
XmNshowArrows: Boolean value if set shows arrows at either end.
XmNorientation: Set to XmHORIZONTAL for a horizontal bar or
XmVERTICAL (default) for a vertical bar.
XmNprocessingDirection: Set to either XmMAX_ON_LEFT or
XmMAX_ON_RIGHT for XmHORIZONTAL orientation, or XmMAX_ON_TOP
or XmMAX_ON_BOTTOM for XmVERTICAL
XmNincrement: The increment per move.
XmNpageIncrement: The increment if a button is pressed in the
arrows or the box. This is defaulted to 10.
XmNdecimalPoint: Shows the decimal point from the right.
Note that all values in the ScrollBar Widget's values are given as
integers. Look at the radio station selection example in Listing 32.7.
A point to note in this listing is that the exit button for the
application is offset on the left and right by 20 pixels. This is done
via the XmATTACH_FORM value for each side (left or right) being offset
by the value in XmNleftOffset and XmNrightOffset, respectively. See
Listing 32.3 on how to attach items to a Form.
Listing 32.7. Using the Scale Widget.
/*
** An application to show the radio station selection via a scale.
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/Scale.h>
#define MAX_SCALE 1080
#define MIN_SCALE 800
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
void myfunction(Widget w, XtPointer dclient, XmScaleCallbackStruct *p);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget aForm;
Widget aScale;
Widget aButton;
XmString xstr; /* for the scale title */
Arg args[5];
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "ScaleMe", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,90,
XmNwidth,240,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNleftOffset,20,
XmNrightAttachment,XmATTACH_FORM,
XmNrightOffset,20,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
/**
*** Create the radio FM selection scale here.
*** Note that since we have to work with integers,
*** we have to set the frequency scale to 10x actual
*** value and then set the decimal point explicitly
*** for the display. No provision is made for selecting
*** odd frequencies.
**/
xstr = XmStringCreateLtoR("Radio Stations", XmSTRING_DEFAULT_CHARSET);
aScale = XtVaCreateManagedWidget("sample it",
xmScaleWidgetClass, aForm,
XmNheight,40,
XmNminimum, 800,
XmNvalue, 1011,
XmNmaximum, 1080,
XmNdecimalPoints,1,
XmNtitleString,xstr,
XmNshowValue,TRUE,
XmNorientation,XmHORIZONTAL,
XmNprocessingDirection,XmMAX_ON_RIGHT,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_WIDGET,
XmNbottomAttachment,aButton,
NULL);
XmStringFree(xstr);
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtAddCallback( aScale, XmNvalueChangedCallback, myfunction, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
void myfunction(Widget w, XtPointer dclient, XmScaleCallbackStruct *p)
{
int k;
k = p->value;
if ((k & 0x1) == 0) /** % 2 is zero ** check limits and increase **/
{
k++;
if (k >= MAX_SCALE) k = MIN_SCALE + 1;
if (k <= MIN_SCALE) k = MAX_SCALE - 1;
XmScaleSetValue(w,k); /** this will redisplay it too **/
}
}
In the case of FM selections, you would want the bar to show odd
numbers. A good exercise for you would be to allow only odd numbers in
the selection. Hint: Use XmNvalueChangedCallback as follows:
XtAddCallback(aScale, XmNvalueChangedCallback, myfunction);
Output is shown in Figure 32.8.
Figure 32.8. Using the Scale Widget.
The callback sends a pointer to the structure of type
XmScaleCallbackStruct to a function called myfunction. A sample
function, myfunction(), follows:
/**
*** Partial listing for not allowing even numbers for FM selection.
**/
#define MAX_SCALE 1080
#define MIN_SCALE 800
static void myfunction(Widget w, XtPointer dclient, XmScaleCallbackStruct *p)
{
int k;
k = p->value;
if ((k & 0x1) == 0) /** % 2 is zero ** check limits and increase **/
{
k++;
if (k >= MAX_SCALE) k = MIN_SCALE + 1;
if (k <= MIN_SCALE) k = MAX_SCALE - 1;
XmScaleSetValue(w,k); /** this will redisplay it too **/
}
}
Text Widgets
This Widget enables the user to type in text and provides full
text-editing capabilities. This text could be multiline or
single-line. If you are sure you want only single-line input from the
user, you can specify the TextField Widget. This is simply a
scaled-down version of the Text Widget. The resources for both are the
same unless explicitly stated. They include the following:
XmNvalue: A character string, just like in C. This is different
from Motif 1.1 or older, in which this value used to be a
compound string. If you have Motif 1.2 or later, this will be
C string.
XmNmarginHeight and XmNmarginWidth: The number of pixels on
either side of the Widget. The default is five pixels.
XmNmaxLength: Sets the limit on the number of characters in the
XmNvalue resource.
XmNcolumns: The number of characters per line.
XmNcursorPosition: The number of characters at the cursor
position from the beginning of the text file.
XmNeditable: Boolean value. If set to TRUE, enables the user to
insert text.
The callbacks for this Widget are
XmNactivateCallback: Called when the user presses the Enter key.
XmNfocusCallback: Called when the Widget receives focus from the
pointer.
XmNlosingFocusCallback: Called when the Widget loses focus from
the pointer.
This Widget has several convenience functions:
XmTextGetString(Widget w) returns a C string (char *).
XmTextSetString(Widget w, char *s) sets a string for a Widget.
XmTextSetEditable(Widget w, Boolean TRUEOrFALSE) sets the
Widget's editable string.
XmTextInsert(Widget w, XmTextPosition pos, char *s) sets the text
at the position defined by pos. This XmTextPosition is an
opaque item defining the index in the text array.
XmTextShowPosition(Widget w, XmTextPosition p) scrolls to show
the rest of the string at position p.
XmTextReplace(Widget w, XmTextPosition from, XmTextPosition to,
char *s) replaces the string starting from the location from
inclusive to the position to, inclusive with the characters
in string s.
XmTextRemove(Widget w) clears the text in a string.
XmTextCopy(Widget w, Time t) copies the currently selected text
to the Motif clipboard. The Time t value is derived from the
most recent XEvent (usually in a callback), which is used by
the clipboard to take the most recent entry.
XmTextCut(Widget w, Time t) is similar to XmTextCopy but removes
the selected text from the text's buffer.
XmTextPaste(Widget w) pastes the contents of the Motif clipboard
onto the text area at the current cursor (insertion)
position.
XmTextClearSelection(Widget w, XmTextPosition p, XmTextPosition
q, Time t) selects the text from location p to location q.
In the following example, you could construct a sample editor
application using the Text Widget. For the layout of the buttons, you
would want to use Widgets of the XmManager class to manage the layout
for you rather than having to do it in your own application. These
Manager Widgets are
XmBulletinBoard
XmRowColumn
XmForm
XmBulletinBoard Widgets
The BulletinBoard class enables the programmer to lay out Widgets by
specifying their XmNx and XmNy resources. These values are relative to
the top-left corner of the BulletinBoard Widget. The BulletinBoard
will not move its child Widgets around by itself. If a Widget resizes,
it's the application's responsibility to resize and restructure its
Widgets on the bulletin board.
The resources for the Widget are as follows:
XmNshadowType: Specifies the type of shadow for this Widget. It
can be set to XmSHADOW_OUT (the default), XmSHADOW_ETCHED_IN,
XmSHADOW_ETCHED_OUT, or XmSHADOW_IN.
XmNshadowThickness: The number of pixels for the shadow. This is
defaulted to 0 to not see a shadow.
XmNallowOverlap: Enables the children to be overlapped as they
are laid on the Widget. This is a Boolean resource and is
defaulted to TRUE.
XmNresizePolicy: Specifies the resize policy for managing itself.
If set to XmRESIZE_NONE, it will not change its size. If set
to XmRESIZE_ANY, the default, it will grow or shrink to
attempt to accommodate all of its children automatically. If
set to XmRESIZE_GROW, it will grow only, never shrink,
automatically.
XmNbuttonFontList: Specifies the font for all XmPushButton
children.
XmNlabelFontList: Specifies the default font for all Widgets
derived from XmLabel.
XmNtextFontList: Specifies the default font for all Text,
TextField, and XmList children.
It also provides the callback XmNfocusCallback, which is called when
any children of the BulletinBoard receive focus.
XmRowColumn Widgets
The XmRowColumn Widget class orders its children in a row-and-column
(or row major) fashion. This is used to set up menus, menu bars, and
radio buttons. The resources provided by this Widget include the
following:
XmNorientation: XmHORIZONTAL for a row major layout of its
children; XmVERTICAL for a column major layout.
XmNnumColumns: Specifies the number of rows for a vertical Widget
and the number of columns for a horizontal Widget.
XmNpacking: Determines how the children are packed. XmPACK_TIGHT
enables the children to specify their own size. It fits
children in a row (or column if XmHORIZONTAL) and then starts
a new row if no space is available. XmPACK_NONE forces
BulletinBoard-like behavior. XmPACK_COLUMN forces all
children to be the size of the largest child Widget. This
uses the XmNnumColumns resource and places all of its
children in an organized manner.
XmNentryAlignment: Specifies which part of the children to use in
its layout alignment. Its default is XmALIGNMENT_CENTER, but
it can be set to XmALIGNMENT_BEGINNING for left or
XmALIGNMENT_END for right side. This is on a per-column
basis.
XmNverticalEntryAlignment: Specifies the alignment on a per-row
basis. It can be assigned a value of
XmALIGNMENT_BASELINE_BOTTOM, XmALIGNMENT_BASELINE_TOP,
XmALIGNMENT_CONTENTS_BOTTOM, XmALIGNMENT_CONTENTS_TOP, or
XmALIGNMENT_CENTER.
XmNentryBorder: The thickness of a border drawn around all
children. Defaulted to 0.
XmNresizeWidth: A Boolean variable. If set to TRUE, will enable
the RowColumn Widget to resize its width when necessary.
XmNresizeHeight: A Boolean variable. If set to TRUE, will enable
the RowColumn Widget to resize its height when necessary.
XmNradioBehaviour: Works with ToggleButtons only. It enables only
one ToggleButton of a group of buttons to be active at time.
The default is FALSE.
XmNisHomogeneous: If set to TRUE, specifies that only children of
the type of class in XmNentryClass can be children of this
Widget. The default is FALSE.
XmNentryClass: Specifies the class of children allowed in this
Widget if XmNisHomogeneous is TRUE.
A sample radio button application was shown in Listing 32.5. To see
another example of the same listing but with two columns, see Listing
32.8.
Listing 32.8. Using RowColumn Widgets.
/*
** This is another Motif application that demonstrates the use of
** a ToggleButton Widget(s) stored on a multicolumn RowColumn Widget.
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/ToggleB.h>
#include <Xm/RowColumn.h>
#include <Xm/PushB.h>
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
#define MAX_BTNS 8
#define NUM_COL 2
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget aForm;
Widget aButton;
Widget aRowCol;
char str[32];
Widget aToggle[MAX_BTNS];
Arg args[5];
int i;
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,150,
XmNwidth,200,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
#define DO_RADIO
/**
*** A quick intro to the hierarchy in Motif.
*** Let's create a RowColumn Widget to place all Toggle
*** Buttons.
*** Note how the RowColumn button attaches itself to
*** the top of the button.
**/
aRowCol = XtVaCreateManagedWidget("rowcol",
xmRowColumnWidgetClass, aForm,
#ifdef DO_RADIO
XmNradioBehavior, TRUE,
XmNradioAlwaysOne, TRUE,
#endif
XmNnumColumns,NUM_COL,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_WIDGET,
NULL);
/**
*** Make ToggleButtons on this form called RowCol. Attach them all
*** RowColumn Widget on top of the form.
***
*** Note the radioBehavior setting
**/
for (i=0; i< MAX_BTNS; i++)
{
sprintf(str,"Button %d",i);
aToggle[i] = XtVaCreateManagedWidget(str,
xmToggleButtonWidgetClass, aRowCol,
XmNradioBehavior, TRUE,
NULL);
}
XmToggleButtonSetState(aToggle[0],True, False);
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
See Figure 32.9.
Figure 32.9. Using the RowColumn Widget.
XmForm Widgets
The beginning of this chapter introduced you to the workings of a Form
Widget. This is the most flexible, but complex, Widget in Motif.
Its resources include
* XmNtopAttachment
* XmNleftAttachment
* XmNrightAttachment
* XmNbottomAttachment
These values specify how a child is assigned in position. The
following values correspond to each of the sides of the Widget:
XmATTACH_NONE: Does not attach this side to Form.
XmATTACH_FORM: Attaches to the corresponding side on Form.
XmATTACH_WIDGET: Attaches this side to the opposite side of a
reference Widget—for example, the right side of this
Widget to the left side of the reference Widget. A reference
Widget is another child on the same form.
XmATTACH_OPPOSITE_WIDGET: Attaches this side to the same side of
a reference Widget. This is rarely used.
XmATTACH_POSITION: Attaches a side by the number of pixels shown
in XmNtopPosition, XmNleftPosition, XmNrightPosition, and
XmNbottomPosition resources, respectively.
XmATTACH_SELF: Uses the XmNx,XmNy,XmNheight, and XmNwidth.
* XmNtopWidget
* XmNleftWidget
* XmNrightWidget
* XmNbottomWidget
These resources are set to the corresponding Widgets for each side for
the XmATTACH_WIDGET setting in an attachment.
* XmNtopOffset
* XmNleftOffset
* XmNrightOffset
* XmNbottomOffset
These resources are the number of pixels a side of a child is offset
from the corresponding Form side. The offset is used when the
attachment is XmATTACH_FORM.
______________________________________________________________
NOTE: Sometimes it's hard to get the settings for a Form Widget
just right, or the Form Widget doesn't lay out the Widgets in what
seems to be the proper setting for a child Widget. In these cases,
try to manage and lay out the children in ascending or descending
order from the origin of the Form Widget. That is, create the
top-left Widget first and use it as an anchor to create the next
child, then the next one to its right, and so on. There is no
guarantee that this will work, so try from the bottom right, bottom
left, or top right for your anchor positions.
If this technique doesn't work, try using two forms on top of the
form with which you are working. Forms are cheap; your time is not.
It's better to just make a form when two or more Widgets have to
reside in a specific layout.
______________________________________________________________
While trying a new layout on a Form Widget, if you get error messages
about failing after 10,000 iterations, you have conflicting layout
requests to a child or children Widgets. Check the attachments very
carefully before proceeding. This error message results from the Form
Widget trying different layout schemes to accommodate your request.
______________________________________________________________
NOTE: At times, conflicting requests to a Form will cause your
application to slow down while it's trying to accommodate your
request, not show the form, or both. At this time, try to remove
your Form settings one at a time until the errors disappear. You
should then be able to weed out the offending resource setting for
that Form.
______________________________________________________________
Designing Layouts
When designing layouts, think about the layout before you start
writing code. Let's try an order entry example. See Listing 32.9.
Listing 32.9. Setting up a simple hierarchy.
/*
** This listing shows how to set up a hierarchy.
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/Label.h>
#include <Xm/Text.h>
#include <Xm/RowColumn.h>
/*** Some items for the list ***/
#define NUMITEMS 4
char *thisLabel[NUMITEMS] = { "Name", "User Id", "Home", "Usage" };
/* For the list Widget, we need compound strings */
XmString xarray[NUMITEMS];
#define USE_SCROLL
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget masterForm;
Widget buttonForm;
Widget labelForm;
Widget inputForm;
Widget labelRC;
Widget textRC;
Widget buttonRC;
Widget inputText[NUMITEMS];
Widget inputLabel[NUMITEMS];
Widget searchBtn;
Widget cancelBtn;
Arg args[15];
int i;
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
masterForm = XtVaCreateManagedWidget("MasterForm",
xmFormWidgetClass, top,
XmNheight,150,
XmNwidth,200,
NULL);
buttonForm = XtVaCreateManagedWidget("ButtonForm",
xmFormWidgetClass, masterForm,
XmNtopAttachment,XmATTACH_POSITION,
XmNtopPosition, 75,
XmNheight,30,
XmNbottomAttachment,XmATTACH_FORM,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
NULL);
labelForm = XtVaCreateManagedWidget("LabelForm",
xmFormWidgetClass, masterForm,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_POSITION,
XmNbottomPosition, 75,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_POSITION,
XmNrightPosition,50,
NULL);
inputForm = XtVaCreateManagedWidget("InputForm",
xmFormWidgetClass, masterForm,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_POSITION,
XmNbottomPosition, 75,
XmNrightAttachment,XmATTACH_FORM,
XmNleftAttachment,XmATTACH_POSITION,
XmNleftPosition,50,
NULL);
/**
*** Now create the RowColumn manager Widgets
**/
buttonRC = XtVaCreateManagedWidget("buttonRC",
xmRowColumnWidgetClass, buttonForm,
XmNbottomAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNorientation, XmHORIZONTAL,
NULL);
labelRC = XtVaCreateManagedWidget("buttonRC",
xmRowColumnWidgetClass, labelForm,
XmNbottomAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNorientation, XmVERTICAL,
NULL);
textRC = XtVaCreateManagedWidget("buttonRC",
xmRowColumnWidgetClass, inputForm,
XmNbottomAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNorientation, XmVERTICAL,
NULL);
for (i = 0; i < NUMITEMS; i++)
{
inputLabel[i] = XtVaCreateManagedWidget(thisLabel[i],
xmLabelWidgetClass, labelRC, NULL);
inputText[i] = XtVaCreateManagedWidget(thisLabel[i],
xmTextWidgetClass, textRC, NULL);
}
searchBtn = XtVaCreateManagedWidget("Search",
xmPushButtonWidgetClass, buttonRC, NULL);
cancelBtn = XtVaCreateManagedWidget("Cancel",
xmPushButtonWidgetClass, buttonRC, NULL);
XtAddCallback( cancelBtn, XmNactivateCallback, bye, (XtPointer) NULL);
/** Add the handler to search here. **/
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
The output of this application is shown in Figure 32.10. Notice how
the labels do not line up with the Text Widget. There is a problem in
the hierarchy of the setup. See the hierarchy of the application in
Figure 32.11.
Figure 32.10. The output of Listing 32.9.
Figure 32.11. The hierarchy of Listing 32.9.
The Form Widgets are created to maintain the relative placements of
all of the Widgets that correspond to a type of functionality. The
RowColumn Widgets allow the placement of items on themselves. The best
route to take in this example would be to lay one text and one label
on one RowColumn Widget and have three RowColumn Widgets in all, one
for each instance up to NUM_ITEMS. This will ensure that each label
lines up with its corresponding text Widget.
Here are a few points to note about laying out applications:
* Think about what the form or dialog is trying to achieve. Draw it
on paper if you have to. Coding is the easy part; determining what
to do is much harder.
* Be consistent. Users will love you for it. If Alt-X is a shortcut
for Exit in one screen, do not make it a Cut operator in another.
Keep controls on the same side of all dialogs and forms. Use
separators to separate different functions on the same window.
* Choose a color scheme for your end users. What may be cool to you
may be grotesque to the end user. They may not even be using a
color monitor in some rare cases. A combination of white, gray,
and black may be your best bet in this case if you do not want to
deal with different color schemes in your code.
* Colors on your monitor may not be the same on the end user's
monitor.
* Do not assume that the user has the same resolution monitor as
yourself. Keep fonts clean, and buttons big enough for a large
cursor. Allow windows to be resized as much as possible to enable
users to customize their desktops.
* Assume nothing. If the user can size your window to an unworkable
size, either limit the size in the resize callback to the lowest
size or do not allow sizing at all.
* Offer some help for the user. In the future, Help will be required
as a standard option on menu bars, so plan ahead.
* Avoid clutter. Too many options and entries on one huge form tend
to confuse and baffle the user. Consider a two-or-more-tiered
approach via dialogs. Default everything as much as possible.
* Allow the program to be more forgiving. Sometimes an "Are you
sure?" dialog with an option to change a list of parameters can be
endearing to the user. On the other hand, some users hate this
type of checking.
Menus
Designing a Widget hierarchy is especially important when working with
Motif menus. Motif menus are a collection of Widgets, so there is no
"menu" Widget for a menu. You create menus using a hierarchy of
different types of Widgets: RowColumn, PushButton, CascadeButton,
ToggleButton, Label, and Separator.
There are three kinds of menus in Motif:
* Pop-up: This appears as a list of items when a pointer button is
pressed on a Widget.
* Pull-down: This appears when a button on an existing menu is
pressed.
* Option: This enables the user to select from a list of options
with the current selection visible at all times.
The procedure to create a menu is different for each type of menu.
Pop-Up Menus
To create a pop-up menu, follow these steps:
1. Include the correct header files. You will need the header files
for the menu:
Label.h
RowColumn.h
PushB.h
Separator.h
BulletinB.h
CascadeB.h
2. Create the menu pane with a call to XmCreatePopupMenu. This is a
convenience call to create RowColumn and MenuShell Widgets with
the proper settings.
3. Create the buttons on the menu pane. Use XmPushbuttons,
XmToggleButtons, XmSeparator, and XmCascadeButtons.
4. Attach callback functions to the Widgets.
Listing 32.10 shows how to set up a simple pop-up menu.
Listing 32.10. Using pop-up menus.
/*
** This listing shows how to set up a pop-up menu.
** Use the left mouse button on the area below the label.
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/BulletinB.h>
#include <Xm/PushB.h>
#include <Xm/Label.h>
#include <Xm/Text.h>
#include <Xm/RowColumn.h>
#include <Xm/CascadeB.h>
#include <Xm/Separator.h>
void showSelection(Widget w, XtPointer clientdata, XtPointer calldata);
XtEventHandler showMenu(Widget w, XtPointer menu, XEvent *x, Boolean f);
/*** Some items for the list ***/
#define NUMITEMS 3
char *thisLabel[NUMITEMS] = { "CD", "Developer", "Release" };
/* For the list widget, we need compound strings */
XmString xarray[NUMITEMS];
Widget menu; /* <-- for the menu */
Widget menuBtn[NUMITEMS]; /* <-- for the menu */
#define USE_SCROLL
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget masterForm;
Widget masterLabel;
Arg args[15];
Widget tmp;
int i;
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Bulletin Board on this-top level widget. This is a nice widget
*** to place other widgets on top of.
**/
masterForm = XtVaCreateManagedWidget("bb1",
xmBulletinBoardWidgetClass, top,
XmNheight,150,
XmNwidth,200,
NULL);
masterLabel = XtVaCreateManagedWidget("Click Me",
xmLabelWidgetClass, masterForm,
XmNheight,50,
XmNwidth,200,
NULL);
/* XtAddCallback( cancelBtn, XmNactivateCallback, bye, (XtPointer) NULL); */
menu = XmCreatePopupMenu(masterLabel, "menu", NULL, 0);
XtRealizeWidget(menu);
/** Add the event handler for managing the popup **/
tmp = XtCreateManagedWidget("Sample", xmLabelWidgetClass, menu, NULL, 0);
tmp = XtCreateManagedWidget("Swp1", xmSeparatorWidgetClass, menu, NULL, 0);
tmp = XtCreateManagedWidget("Btn1", xmPushButtonWidgetClass, menu, NULL, 0);
XtAddCallback(tmp,XmNactivateCallback, showSelection, NULL);
tmp = XtCreateManagedWidget("Btn2", xmPushButtonWidgetClass, menu, NULL, 0);
XtAddCallback(tmp,XmNactivateCallback, showSelection, NULL);
tmp = XtCreateManagedWidget("Btn3", xmPushButtonWidgetClass, menu, NULL, 0);
XtAddCallback(tmp,XmNactivateCallback, showSelection, NULL);
XtAddEventHandler( masterForm, ButtonPressMask, True, (XtEventHandler)showMenu,
menu);
tmp = XtCreateManagedWidget("Quit", xmPushButtonWidgetClass, menu, NULL, 0);
XtAddCallback(tmp,XmNactivateCallback, bye, NULL);
/** Add the handler to search here. **/
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
/**
*** This function will display the pop-up menu on the screen
**/
XtEventHandler showMenu(Widget w, XtPointer menu, XEvent *event, Boolean f)
{
printf ("\n showing position ");
switch (event->xbutton.button)
{
case Button1: printf(" button 1"); break;
case Button2: printf(" button 2"); break;
case Button3: printf(" button 3"); break;
default: printf(" %d", event->xbutton.button); break;
}
if((event->xbutton.button == Button1)
|| (event->xbutton.button == Button2))
{
XmMenuPosition(menu, (XButtonPressedEvent *)event);
printf(" Managing %ld", (long)menu);
XtManageChild(menu);
}
}
/**
*** This echos the selection on the controlling terminal
**/
void showSelection(Widget w, XtPointer clientdata, XtPointer calldata)
{
printf("\n %s ", XtName(w));
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
Note three important items about this listing:
* You can use printf functions within Motif applications. The output
goes to the controlling terminal by default. This is invaluable in
debugging.
* The menu is not visible by itself. An event handler on the menu's
parent is registered before the menu can be displayed. This
enables the menu to be displayed whenever a button is pressed.
* The XmMenuPosition call sets the position of the pop-up menu. It
is then managed (that is, after placement).
The Menu Bar
A menu bar is a horizontal bar that is always available to the user.
Motif uses the RowColumn Widget as a bar with cascading buttons on it
for each option.
The procedure for creating a menu bar is as follows:
1. Include the correct header files. You will need the header files
for the menu:
Label.h
RowColumn.h
PushB.h
Separator.h
BulletinB.h
CascadeB.h
2. Create the menu bar with a call to XmCreateMenuBar().
3. Create the pull-down menu panes with a call to
XmCreatePulldownMenu().
4. For each pull-down pane, create a cascade button on the menu bar.
Use the menu bar as the parent. A cascade button is used to link
the items in a menu with the menu bar itself.
5. Attach the menu pane to its corresponding cascade button. Use the
XmNsubMenuId resource of the cascade button to the appropriate
menu pane.
6. Create the menu entries in the menu panes.
Listing 32.11 shows you how to set up a simple menu application.
Listing 32.11. Creating a menu bar.
/*
** This listing shows how to set up a menu bar and pulldown menus
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/Label.h>
#include <Xm/Text.h>
#include <Xm/RowColumn.h>
#include <Xm/CascadeB.h>
#include <Xm/Separator.h>
void doBackup(Widget w, XtPointer x, XtPointer c)
{
printf("\n Start backup ");
}
void doRestore(Widget w, XtPointer x, XtPointer c)
{
printf("\n Start restore ");
}
void bye(Widget w, XtPointer x, XtPointer c)
{
exit(0);
}
void selectTape(Widget w, XtPointer x, XtPointer c)
{
printf("\n Select tape drive...");
}
void selectDisk(Widget w, XtPointer x, XtPointer c)
{
printf("\n Select Floppy disks...");
}
void helpBtn(Widget w, XtPointer x, XtPointer c)
{
printf("\n ... No help available ");
}
int main (int argc, char*argv[])
{
Widget top;
XtAppContext app;
Widget masterForm;
Widget menu; /* for the menu bar */
Widget submenu; /* for pulldown menus */
Widget cascade; /* for cascade button on the menu bar */
Widget filler;
Arg args[10];
int n;
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
masterForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,150,
XmNwidth,200,
NULL);
n = 0;
XtSetArg(args[n],XmNheight, 50); n++;
menu = XmCreateMenuBar(masterForm,"mastermenu",
args, n);
submenu = XmCreatePulldownMenu(menu,"submenupane1", NULL, 0);
cascade = XtVaCreateManagedWidget("File",
xmCascadeButtonWidgetClass, menu,
XmNsubMenuId, submenu,
NULL);
filler = XtVaCreateManagedWidget("Backup",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, doBackup, (XtPointer) NULL);
filler = XtVaCreateManagedWidget("Restore",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, doRestore, (XtPointer) NULL);
filler = XtVaCreateManagedWidget("Quit",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, bye, (XtPointer) NULL);
submenu = XmCreatePulldownMenu(menu,"submenupane2", NULL, 0);
cascade = XtVaCreateManagedWidget("Options",
xmCascadeButtonWidgetClass, menu,
XmNsubMenuId, submenu,
NULL);
filler = XtVaCreateManagedWidget("Tape",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, selectTape, (XtPointer) NULL);
filler = XtVaCreateManagedWidget("Floppy",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, selectDisk, (XtPointer) NULL);
submenu = XmCreatePulldownMenu(menu,"submenupane3", NULL, 0);
cascade = XtVaCreateManagedWidget("Help",
xmCascadeButtonWidgetClass, menu,
XmNsubMenuId, submenu,
NULL);
filler = XtVaCreateManagedWidget("Floppy",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, selectDisk, (XtPointer) NULL);
XtVaSetValues( menu,
XmNmenuHelpWidget, cascade,
NULL);
XtAddCallback( cascade, XmNactivateCallback, helpBtn ,NULL);
XtManageChild(menu);
/** Add the handler to search here. **/
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
Note that the Motif programming style requires you to provide the Help
button (if you have any) to be right-justified on the menu bar. This
Help Cascade button should then be set to the XmNmenuHelpWidget of a
menu bar. The menu bar will automatically position this Widget to the
right-hand side of the visible bar. See Listing 32.12 on how to create
pull-down menu items on a menu items on a menu bar.
Listing 32.12. Creating menu bars with pull-down menu items.
/*
** This listing shows how to set up a menu bar and pull-down menus
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/Label.h>
#include <Xm/Text.h>
#include <Xm/RowColumn.h>
#include <Xm/CascadeB.h>
#include <Xm/Separator.h>
void doBackup(Widget w, XtPointer x, XtPointer c)
{
printf("\n Start backup ");
}
void doRestore(Widget w, XtPointer x, XtPointer c)
{
printf("\n Start restore ");
}
void bye(Widget w, XtPointer x, XtPointer c)
{
exit(0);
}
void selectTape(Widget w, XtPointer x, XtPointer c)
{
printf("\n Select tape drive...");
}
void selectDisk(Widget w, XtPointer x, XtPointer c)
{
printf("\n Select Floppy disks...");
}
void helpBtn(Widget w, XtPointer x, XtPointer c)
{
printf("\n ... No help available ");
}
int main (int argc, char*argv[])
{
Widget top;
XtAppContext app;
Widget masterForm;
Widget menu; /* for the menu bar */
Widget submenu; /* for pull-down menus */
Widget cascade; /* for CascadeButton on the menu bar */
Widget filler;
Arg args[10];
int n;
/**
*** Intialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
masterForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,150,
XmNwidth,200,
NULL);
n = 0;
XtSetArg(args[n],XmNheight, 50); n++;
menu = XmCreateMenuBar(masterForm,"mastermenu",
args, n);
/********************** The change is here ******************/
n = 0;
XtSetArg(args[n],XmNtearOffModel, XmTEAR_OFF_ENABLED); n++;
submenu = XmCreatePulldownMenu(menu,"submenupane1", args, n);
/********************** The change is here ******************/
cascade = XtVaCreateManagedWidget("File",
xmCascadeButtonWidgetClass, menu,
XmNsubMenuId, submenu,
NULL);
filler = XtVaCreateManagedWidget("Backup",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, doBackup, (XtPointer) NULL);
filler = XtVaCreateManagedWidget("Restore",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, doRestore, (XtPointer) NULL);
filler = XtVaCreateManagedWidget("Quit",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, bye, (XtPointer) NULL);
submenu = XmCreatePulldownMenu(menu,"submenupane2", NULL, 0);
cascade = XtVaCreateManagedWidget("Options",
xmCascadeButtonWidgetClass, menu,
XmNsubMenuId, submenu,
NULL);
filler = XtVaCreateManagedWidget("Tape",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, selectTape, (XtPointer) NULL);
filler = XtVaCreateManagedWidget("Floppy",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, selectDisk, (XtPointer) NULL);
submenu = XmCreatePulldownMenu(menu,"submenupane3", NULL, 0);
cascade = XtVaCreateManagedWidget("Help",
xmCascadeButtonWidgetClass, menu,
XmNsubMenuId, submenu,
NULL);
filler = XtVaCreateManagedWidget("Floppy",
xmPushButtonWidgetClass, submenu, NULL);
XtAddCallback( filler, XmNactivateCallback, selectDisk, (XtPointer) NULL);
XtVaSetValues( menu,
XmNmenuHelpWidget, cascade,
NULL);
XtAddCallback( cascade, XmNactivateCallback, helpBtn ,NULL);
XtManageChild(menu);
/** Add the handler to search here. **/
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
The Options Menu
An Options menu enables the user to select from a list of items while
displaying the most recently selected item. The procedure for creating
an Options menu is similar to creating menu bars:
1. Include the correct header files. You will need the header files
for the menu:
Label.h
RowColumn.h
PushB.h
Separator.h
BulletinB.h
CascadeB.h
2. Create the menu bar with a call to XmCreateOptionMenu().
3. Create the pull-down menu panes with a call to
XmCreatePulldownMenu().
4. For each pull-down pane, create a CascadeButton on the menu bar.
5. Attach the menu pane to its corresponding CascadeButton. Use the
XmNsubMenuId resource of the CascadeButton to the appropriate menu
pane.
6. Create the menu entries in the menu panes.
Accelerators and Mnemonics
An accelerator for a command is the keystroke that invokes the
callback for that particular menu item. For example, for opening a
file, you could use Ctrl-O. The resource for this accelerator could be
set in the resource file as
*Open*accelerator: Ctrl<Key>O
The corresponding menu item should read "Open Ctrl+O" to let the user
know about this shortcut. Note the + instead of -. You can also set
this resource via the command in the .Xresources file:
*Open*acceleratorText: "Ctrl+O"
Using the .Xresource file is the preferred way of setting these
resources.
Mnemonics are a short form for letting the user select menu items
without using the mouse. For example, the user could press <meta>F to
invoke the File menu. These are also usually set in the .Xresource
file. The syntax for the File menu to use the <meta>F key would be:
*File*mnemonic:F
______________________________________________________________
NOTE: With Linux on your PC, meta means the Alt key.
______________________________________________________________
Dialog Boxes
A dialog box is used to convey information about something to the user
and requests a canned response in return. For example, a dialog box
might say "Go ahead and Print" and present three buttons—OK,
Cancel, and Help. The user must then select one of the three buttons
to process the command.
A typical dialog box displays an icon, a message string, and usually
three buttons (OK, Cancel, and Help). Motif provides predefined dialog
boxes for the following categories:
* Errors
* Information
* Warnings
* Working
* Questions
Each of these dialog box types displays a different icon: a question
mark for the Question dialog box, an exclamation mark for an
Information dialog box, and so on. Convenience functions ease the
creation of dialog boxes. These are
* XmCreateErrorsDialog
* XmCreateInformationDialog
* XmCreateWarningDialog
* XmCreateWorkingDialog
* XmCreateQuestionDialog
The infamous "OK to quit?" dialog box can be implemented as shown in
Listing 32.13. There is another example in Listing 32.17.
Listing 32.13. Code fragment to confirm quit command.
/*
** Confirm quit one last time
*/
void reallyQuit(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
void confirmQuit(Widget w, XtPointer clientdata, XtPointer calldata)
{
static Widget quitDlg = NULL;
static char *msgstr = "Really Quit?"
if (quitDlg != NULL)
{
/* first time called */
quitDlg = XmCreateQuestionDialog(w,"R U Sure",NULL,0);
XtVaSetValues(quitDlg, XtVaTypedArg,
XmNmessageString,
XmRString,
msgstr,
strlen(msgstr),
NULL);
XtAddCallback(quitDlg, reallyQuit, NULL);
}
XtManageChild(quitDlg);
}
Append this code fragment to the end of any sample listings in this
chapter to get instant checking before you actually quit the
application. Note that the quitDlg dialog box is set to NULL when the
function is first called. It does not have to be re-created on every
call after the first one; it is only managed for all subsequent calls
to this function.
Modes of a Dialog Box
A dialog box can have four modes of operation, called modality. The
mode is set in the XmNdialogStyle resource. The possible values are
* Nonmodal: The user can ignore the dialog box and work with any
other window on the screen. Resource value is XmDIALOG_MODELESS.
* Primary Application Modal: All input to the window that invoked
the dialog box is locked out. The user can use the rest of the
windows in the application. Resource value is
XmDIALOG_PRIMARY_APPLICATION_MODAL.
* Full Application Modal: All input to all the windows in the
application that invoked the dialog box is locked out. The user
cannot use the rest of the windows in the application. Resource
value is XmDIALOG_FULL_APPLICATION_MODAL.
* System Modal: All input is directed to the dialog box. The user
cannot interact with any other window in the system. Resource
value is XmDIALOG_SYSTEM_MODAL.
The dialog boxes provided by Motif are based on the XmMessageBox
Widget. Sometimes it is necessary to get to the Widgets in a dialog
box. This is done with a call to XmMessageBoxGetChild( Widget dialog,
typeOfWidget); where typeOfWidget can be one of the following:
XmDIALOG_HELP_BUTTON XmDIALOG_CANCEL_BUTTON
XmDIALOG_SEPARATOR XmDIALOG_MESSAGE_LABEL
XmDIALOG_OK_BUTTON XmDIALOG_SYMBOL_LABEL
The dialog box may have more Widgets that can be addressed. Check the
man pages for the descriptions of these Widgets. For example, to hide
the Help button on a dialog box, use the call
XtUnmanageChild(XmMessageBoxGetChild(dlg, XmDIALOG_HELP_BUTTON));
or, in the case of adding a callback, use
XtAddCallback(XmMessageBoxGetChild(dlg, XmDIALOG_OK_BUTTON),
XmNactivateCallback, yourFunction);
A typical method of creating custom dialog boxes is to use existing
ones. Then, using the XmMessageBoxGetChild function, you can add or
remove any function you want. For example, by replacing the message
string Widget with a Form Widget, you have a place for laying out
Widgets however you need to.
Events
An event is a message sent from the X server to the application that
some condition in the system has changed. This could be a button
press, a keystroke, requested information from the server, or a
timeout. An event is always relative to a window and starts from the
bottom up. It propagates up the window hierarchy until it gets to the
root window, where the root window application makes the decision to
either use or discard it. If an application in the hierarchy does use
the event or does not allow upward propagation of events, the message
is used at the window itself. Only device events are propagated upward
(such as keyboard or mouse)—not configuration events.
An application must request an event of a particular type before it
can begin receiving events. Each Motif application calls
XtAppInitialize to create this connection automatically.
Events contain at least the following information :
* The type of event
* The display where it happened
* The window of the event, called the event window
* The serial number of the last event processed by the server
Look in the file <X11/Xlib.h> for a description of the union called
XEvent, which enables access to these values. The file <X11/X.h>
contains the descriptions of constants for the types of events. All
event types share the header:
typedef struct {
int type;
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display;/* display the event was read from */
Window window; /* window on which event was requested in event mask */
} XAnyEvent;
Expose Events
The server generates an Expose when a window that was covered by
another is brought to the top of the stack, or even partially exposed.
The structure for this event type is
typedef struct {
int type; /* type of event */
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display; /* display the event was read from */
Window window;
int x, y;
int width, height;
int count; /* if nonzero, at least this many more */
} XExposeEvent;
Note how the first five fields are shared between this event and
XAnyEvent. Expose events are guaranteed to be in sequence. An
application may get several Expose events from one condition. The
count field keeps a count of the number of Expose events still in the
queue when the application receives this one. Thus, it can be up to
the application to wait to redraw until the last Expose event is
received (that is, count == 0).
Pointer Events
A Pointer event is generated by a mouse press, release, or movement.
The type of event is called XButtonEvent. Recall that the leftmost
button is Button1, but it can be changed. The structure returned by
this button press and release is
typedef struct {
int type; /* of event */
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display; /* display the event was read from */
Window window; /* "event" window it is reported relative to */
Window root; /* root window that the event occured on */
Window subwindow; /* child window */
Time time; /* milliseconds */
int x, y; /* pointer x, y coordinates in event window */
int x_root, y_root; /* coordinates relative to root */
unsigned int state; /* key or button mask */
unsigned int button; /* detail */
Bool same_screen; /* same screen flag */
} XButtonEvent;
typedef XButtonEvent XButtonPressedEvent;
typedef XButtonEvent XButtonReleasedEvent;
The event for a movement is called XMotionEvent, with the type field
set to MotionNotify.
typedef struct {
int type; /* MotionNotify */
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display; /* display the event was read from */
Window window; /* "event" window reported relative to */
Window root; /* root window that the event occured on */
Window subwindow; /* child window */
Time time; /* milliseconds */
int x, y; /* pointer x, y coordinates in event window */
int x_root, y_root; /* coordinates relative to root */
unsigned int state; /* key or button mask */
char is_hint; /* detail */
Bool same_screen; /* same screen flag */
} XMotionEvent;
typedef XMotionEvent XPointerMovedEvent;
Keyboard Events
A keyboard event is generated when the user presses or releases a key.
Both types of events, KeyPress and KeyRelease, are returned in a
XKeyEvent structure.
typedef struct {
int type; /* of event */
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display; /* display the event was read from */
Window window; /* "event" window it is reported relative to */
Window root; /* root window that the event occured on */
Window subwindow; /* child window */
Time time; /* milliseconds */
int x, y; /* pointer x, y coordinates in event window */
int x_root, y_root; /* coordinates relative to root */
unsigned int state; /* key or button mask */
unsigned int keycode; /* detail */
Bool same_screen; /* same screen flag */
} XKeyEvent;
typedef XKeyEvent XKeyPressedEvent;
typedef XKeyEvent XKeyReleasedEvent;
The keycode field gives information on whether the key was pressed or
released. These constants are defined in <X11/keysymdef.h> and are
vendor-specific. These are called KeySym and are generic across all X
servers. For example, the F1 key could be described as XK_F1. The
function XLookupString converts a KeyPress event into a string and a
KeySym (a portable key symbol). The call is
int XLookupString(XKeyEvent *event,
char *returnString,
int max_length,
KeySym *keysym,
XComposeStatus *compose);
The returned ASCII string is placed in returnString for up to
max_length characters. The keysym contains the key symbol. Generally,
the compose parameter is ignored.
Window Crossing Events
The server generates crossing EnterNotify events when a pointer enters
a window and LeaveNotify events when a pointer leaves a window. These
are used to create special effects for notifying the user that the
window has focus. The XCrossingEvent structure looks like the
following:
typedef struct {
int type; /* of event */
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display; /* display the event was read from */
Window window; /* "event" window reported relative to */
Window root; /* root window that the event occured on */
Window subwindow; /* child window */
Time time; /* milliseconds */
int x, y; /* pointer x, y coordinates in event window */
int x_root, y_root; /* coordinates relative to root */
int mode; /* NotifyNormal, NotifyGrab, NotifyUngrab */
int detail;
/*
* NotifyAncestor, NotifyVirtual, NotifyInferior,
* NotifyNonlinear, NotifyNonlinearVirtual
*/
Bool same_screen; /* same screen flag */
Bool focus; /* boolean focus */
unsigned int state; /* key or button mask */
} XCrossingEvent;
typedef XCrossingEvent XEnterWindowEvent;
typedef XCrossingEvent XLeaveWindowEvent;
These are generally used to color a window on entry and exit to
provide feedback to the user as he moves the pointer around.
Event Masks
An application requests events of a particular type by calling a
function named XAddEventHandler(). The prototype for this function is
XAddEventHandler( Widget ,
EventMask ,
Boolean maskable,
XtEventHandler handlerfunction,
XtPointer clientData);
The handler function is of the form
void handlerFunction( Widget w, XtPointer clientData,
XEvent *ev, Boolean *continueToDispatch);
The first two arguments are the clientdata and Widget passed in
XtAddEventHandler. The ev argument is the event that triggered this
call. The last argument enables this message to be passed to other
message handlers for this type of event. This should be defaulted to
TRUE.
You would use the following call on a Widget w to be notified of all
pointer events of the type ButtonMotion and PointerMotion on this
Widget.
extern void handlerFunction( Widget w, XtPointer clientData,
XEvent *ev, Boolean *continueToDispatch);
XAddEventHandler( w, ButtonMotionMask | PointerMotionMask, FALSE,
handlerFunction, NULL );
The possible event masks are
* NoEventMask
* KeyPressMask
* KeyReleaseMask
* ButtonPressMask
* ButtonReleaseMask
* EnterWindowMask
* LeaveWindowMask
* PointerMotionMask
* PointerMotionHintMask
* Button1MotionMask
* Button2MotionMask
* Button3MotionMask
* Button4MotionMask
* Button5MotionMask
* ButtonMotionMask
* KeymapStateMask
* ExposureMask
* VisibilityChangeMask
* StructureNotifyMask
* ResizeRedirectMask
* SubstructureNotifyMask
* SubstructureRedirectMask
* FocusChangeMask
* PropertyChangeMask
* ColormapChangeMask
* OwnerGrabButtonMask
Listing 32.14 is a sample application that shows how to track the
mouse position.
Listing 32.14. Tracking a pointer.
/*
** This application shows how to track a pointer
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/Label.h>
static int track;
void upMouse(Widget w, XtPointer clientdata, XEvent *x, Boolean *f)
{
track = 0;
}
void moveMouse(Widget w, XtPointer clientdata, XEvent *x, Boolean *f)
{
if (track == 1)
{
printf("\n x: %d, y: %d", x->xmotion.x, x->xmotion.y);
}
}
void downMouse(Widget w, XtPointer clientdata, XEvent *x, Boolean *f)
{
track = 1;
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget aForm;
Widget aLabel;
Widget aButton;
Arg args[5];
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,90,
XmNwidth,200,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNleftOffset,20,
XmNrightAttachment,XmATTACH_FORM,
XmNrightOffset,20,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
/**
*** Now let's create the label for us.
*** The alignment is set to right-justify the label.
*** Note how the label is attached to the parent form.
**/
aLabel = XtVaCreateManagedWidget("This is a Label",
xmLabelWidgetClass, aForm,
XmNalignment, XmALIGNMENT_END,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_WIDGET,
XmNbottomWidget,aButton,
NULL);
/**
*** Now add the event handlers for tracking the mouse on the
*** label. Note that the LeaveWindowMask is set to release
*** the pointer for you should you keep the button pressed
*** and leave the window.
**/
XtAddEventHandler( aLabel, ButtonPressMask, FALSE, downMouse, NULL);
XtAddEventHandler( aLabel, ButtonMotionMask, FALSE, moveMouse, NULL);
XtAddEventHandler( aLabel, ButtonReleaseMask | LeaveWindowMask,
FALSE, upMouse, NULL);
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
Managing the Queue
Managing the X server is critical if you have to handle lots of
incoming events. The XtAppMainLoop() function handles all the incoming
events via the following functions:
* XtAppPending checks the queue to see if any events are pending.
* XtAppNextEvent removes the next event from the queue.
* XtDispatchEvent passes the message to the appropriate window.
The loop can do something else between checking and removing messages
via the replacement code segment:
while (!done)
{
while (XtAppPending( applicationContext))
{
XtAppNextEvent( applicationContext, &ev));
XtDispacthEvent( &ev));
}
done = interEventFunction();
}
There are some caveats with this scheme:
* This is a nonblocking function. It must be fed at all times with
events, or it will take over all other applications' time.
* There is no guarantee when your inter-event function will be run
if the queue is flooded with events.
* Note the while loop for checking messages. It's more efficient to
flush the queue first and then call your function rather than
calling it once every time you check for messages.
* The inter-event function must be fast or you will see the user
interface slow down. If you want to give some response back to
your user about what's going on while in a long inter-event
function, you can make a call to XmUpdateDisplay( Display *). This
will handle only the Expose events in the queue so that you can
update some status display.
______________________________________________________________
NOTE: Consider using the select call to handle incoming events of
file descriptors. This is a call that enables an application to
wait for events from various file descriptors on read-ready,
write-ready, or both. The file descriptors can be sockets, too!
See the man page for more information on the select call.
Open all the files with an open call.
Get the file descriptor for the event queue.
Use the Select macros to set up the parameters for select call ret
= return from the select function:
switch (ret)
case 0:
process the event queue
case 1: ...
process the file descriptor
______________________________________________________________
Work Procedures
These are functions called by the event-handler loop whenever no
events are pending in the queue. The function is expected to return a
Boolean value indicating whether it has to be removed from the loop
after it is called. If TRUE, it wants to be removed; if FALSE, it
wants to be called again. For example, you could set up a disk file
transfer to run in the background, which will keep returning FALSE
until it is done, at which time it will return TRUE.
The work procedures are defined as
Boolean yourFunction(XtPointer clientdata);
The way to register a work procedure is to call
XtWorkProcId XtAppAddWorkProc ( XtAppContext app,
XtWorkProc functionPointer,
XtPointer clientData);
The return ID from this call is the handle to the work procedure. It
is used to remove the work procedure with a call to the function
XtRemoveWorkProc( XtWorkProcId id);.
Using Timeouts
A timeout is used to perform some task at (almost) regular intervals.
Applications set up a timer callback function that is called when a
requested time interval has passed. This function is defined as
void thyTimerCallback( XtPointer clientdata, XtInterval *tid);
where clientdata is a pointer to client-specific data. The setup
function for the timeout returns the timer ID and is defined as
XtIntervalId XtAddTimeOut ( XtAppContext app,
int milliseconds,
XtTimerCallback TimerProcedure,
XtPointer clientdata);
This call sets up a timer to call the TimerProcedure function when the
requested milliseconds have passed. It will do this only once. If you
want cyclic timeouts—for example, in a clock application—you
have to explicitly set up the next function call in the timer handler
function itself. So generally, the last line in a timer handler is a
call to set a timeout for the next time the function wants to be
called.
Linux is not designed for real-time applications, and you can't expect
a deterministic time interval between successive timer calls. Some
heavy graphics updates can cause delays in the timer loop. For
user-interface applications, the delays are probably not a big
drawback; however, consult your vendor before you attempt to write a
time-critical control application. Depending on your application, your
mileage may vary. See Listing 32.15 for an example of setting up
cyclic timers.
Listing 32.15. Setting up cyclic timers.
/*
** This application shows how to set a cyclic timer
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/Text.h>
int counter;
char buf[32];
#define ONE_SECOND 1000L /* **APPROXIMATELY** 1000 milliseconds..*/
/* Timing is *not* precise in Motif... so do not rely on this time
** for a time-critical application. Use interrupt handlers instead.
*/
void makeTimer(Widget w, XtIntervalId id);
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Widget aForm;
Widget aText;
Widget aButton;
Arg args[5];
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,90,
XmNwidth,200,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNleftOffset,20,
XmNrightAttachment,XmATTACH_FORM,
XmNrightOffset,20,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
/**
*** Now let's create the label for us.
*** The alignment is set to right-justify the label.
*** Note how the label is attached to the parent form.
**/
aText = XtVaCreateManagedWidget("This is a Label",
xmTextWidgetClass, aForm,
XmNalignment, XmALIGNMENT_CENTER,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_WIDGET,
XmNbottomWidget,aButton,
NULL);
/**
*** Now add the timer handler
**/
counter = 0;
makeTimer(aText, (XtIntervalId )NULL);
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
/** This function creates the timer code. **/
void makeTimer(Widget w, XtIntervalId id)
{
Widget tmp;
extern int counter;
sprintf(buf,"%4d",counter++);
XmTextSetString(w,buf);
if (counter < 10) /** reinvoke yourself if < 10 times **/
XtAppAddTimeOut( XtWidgetToApplicationContext(w), ONE_SECOND,
(XtTimerCallbackProc)makeTimer, (XtPointer)w);
}
Handling Other Sources
The XtAddInput function is used to handle inputs from sources other
than the event queue. The definition is
XtInputId XtAddInput( XtAppContext app,
int LinuxfileDescriptor,
XtPointer condition,
XtInputCallback inputHandler,
XtPointer clientdata);
The return value from this call is the handle to the inputHandler
function. This is used to remove the call via the call
XtRemoveInput( XtInput Id);
The inputHandler function itself is defined as
void InputHandler(XtPointer clientdata, int *fd, XtInputId *id);
Unlike timers, you have to register this function only once. Note that
a pointer to a file descriptor is passed in to the function. The file
descriptor must be a Linux file descriptor. You do not have support
for Linux IPC message queues or semaphores through this scheme. The
IPC mechanism is considered dated and is limited to one machine.
Consider using sockets instead.
______________________________________________________________
NOTE: AIX enables pending on message queues via the select call.
Look at the AIX man pages for this call.
______________________________________________________________
The Graphics Context
Each Widget draws itself on the screen using its set of drawing
parameters called the graphics context (GC). For drawing on a Widget,
you can use the X primitive functions if you have its window and its
graphics context. It's easier to limit your artwork to the DrawingArea
Widget, which is designed for this purpose. You can think of the GC as
your paintbrush and the Widget as the canvas. The color and thickness
of the paintbrush are just some of the factors that determine how the
paint is transferred to the canvas.
The function call to create a GC is to use
GC XCreateGC (Display dp, Drawable d, unsigned long mask, XGCValue *values);
For use with a Widget w, this call would look like this:
GC gc;
XGCVvalue gcv;
unsigned long mask;
gc = XCreate(XtDisplay(w), DefaultRootWindow(XtDisplay(w)),
mask, gcv);
Also, you can create a GC for a Widget directly with a call to
XtGetGC(). The prototype for this function is
gc = XtGetGC (Widget w, unsigned long mask, XGCValue *values);
The values for the mask parameter are defined as an ORed value of the
following definitions:
* GCFunction
* GCPlaneMask
* GCForeground
* GCBackground
* GCLineWidth
* GCLineStyle
* GCCapStyle
* GCJoinStyle
* GCFillStyle
* GCFillRule
* GCTile
* GCStipple
* GCTileStipXOrigin
* GCTileStipYOrigin
* GCFont
* GCSubWindowMode
* GCGraphicsExposures
* GCClipXOrigin
* GCClipYOrigin
* GCClipMask
* GCDashOffset
* GCDashList
* GCArcMode
So, if a call is going to set the Font and Clipping mask, the value of
the mask will be (GCFont | GCClipMask). The data structure for setting
the graphics context is as follows:
typedef struct {
int function; /* logical operation */
unsigned long plane_mask;/* plane mask */
unsigned long foreground;/* foreground pixel */
unsigned long background;/* background pixel */
int line_width; /* line width */
int line_style; /* LineSolid, LineOnOffDash, LineDoubleDash */
int cap_style; /* CapNotLast, CapButt,
CapRound, CapProjecting */
int join_style; /* JoinMiter, JoinRound, JoinBevel */
int fill_style; /* FillSolid, FillTiled,
FillStippled, FillOpaeueStippled */
int fill_rule; /* EvenOddRule, WindingRule */
int arc_mode; /* ArcChord, ArcPieSlice */
Pixmap tile; /* tile pixmap for tiling operations */
Pixmap stipple; /* stipple 1 plane pixmap for stipping */
int ts_x_origin; /* offset for tile or stipple operations */
int ts_y_origin;
Font font; /* default text font for text operations */
int subwindow_mode; /* ClipByChildren, IncludeInferiors */
Bool graphics_exposures;/* boolean, should exposures be generated */
int clip_x_origin; /* origin for clipping */
int clip_y_origin;
Pixmap clip_mask; /* bitmap clipping; other calls for rects */
int dash_offset; /* patterned/dashed line information */
char dashes;
} XGCValues;
If you want to set a value in a GC, you have to take two steps before
you create the GC:
1. Set the value in the XGCValue structure.
2. Set the mask for the call.
Let's look at the values of the functions in a bit more detail.
GCFunction
This determines how the GC paints to the screen. The dst pixels are
the pixels currently on the screen, and the src pixels are those that
your application is writing using the GC.
GXclear dst = 0
GXset dst = 1
GXand dst = src AND dst
Gxor dst = src OR dst
GXcopy dst = src
GXnoop dst = dst
Gxnor dst = NOT(src OR dst)
Gxxor dst = src XOR dst
GXinvert dst = NOT dst
GxcopyInverted dst = NOT src
The function for a GC is changed via a call to XSetFunction ( Display
*dp, GC gc, int function), where function is set to one of the values
just mentioned. The default value is GXcopy. There are several other
masks that you can apply. They are listed in the <X11/X.h> file.
GCPlaneMask
The plane mask sets which planes of a drawable can be set by the GC.
This is defaulted to AllPlanes, thereby enabling the GC to work with
all planes on a Widget.
GCForeground & GCBackground
These are the values of the pixels to use for the foreground and
background colors, respectively. The call to manipulate these is
XSetForeGround(Display *dp, GC gc, Pixel pixel);
XSetBackGround(Display *dp, GC gc, Pixel pixel);
GCLineWidth
This is the number of pixels for the width of all lines drawn via the
GC. It is defaulted to zero, which is the signal to the server to draw
the thinnest line possible.
GCLineStyle GCDashOffset GCDashList
This determines the style of the line drawn on-screen. LineSolid draws
a solid line using the foreground color, LineOnOffDash draws an
intermittent line with the foreground color, and LineDoubleDash draws
a line that is composed of interlaced segments of the foreground and
background colors. The GCDashOffset and GCDashList values determine
the position and length of these dashes.
GCCapStyle
This determines how the server draws the ends of lines. CapNotLast
draws up to, but does not include, the endpoint pixels of a line;
CapButt draws up to the endpoints of a line (inclusive); CapRound
tries to round off the edges of a thick line (three or more pixels
wide); and CapProjecting extends the endpoint a little.
GCJoinStyle
This is used to draw the endpoints of a line. It can be set to
JointMiter for a 90-degree joint, JoinBevel for a beveled joint, or
JoinRound for a rounded joint.
GCFillStyle, GCTile, GCStipple
The fill style can be set to FillSolid, which specifies the fill color
to be the foreground color; FillTiled specifies a pattern of the same
in the Tile attribute; and FillStipple specifies a pattern in the
Stipple attribute. FillStipple uses the foreground color where a bit
is set to 1 and nothing when a bit is set to 0, whereas
FillOpaqueStippled uses the foreground color when a bit is set to 1
and the background color when a bit is set to 0.
GCFont
This specifies the fontlist to use. (See the section, "Using Fonts and
FontLists," later in this chapter.)
GCArcMode
This defines the way an arc is drawn on-screen (see the next section).
Drawing Lines, Points, Arcs, and Polygons
Motif applications can access all the graphics primitives provided by
Xlib. All Xlib functions must operate on a window or a pixmap; both
are referred to as drawable. Widgets have a window after they are
realized. You can access this window with a call to XtWindow(). An
application can crash if Xlib calls are made to a window that is not
realized. The way to check is via a call to XtIsRealized() on the
Widget, which will return TRUE if it is realized and FALSE if it is
not. Use the XmDrawingArea Widget's callbacks for rendering your
graphics, because it is designed for this purpose. The callbacks
available to you are
* XmNresizeCallback: Invoked when the Widget is resized.
* XmNexposeCallback: Invoked when the Widget receives an Expose
event.
* XmNinputCallback: Invoked when a button or key is pressed on the
Widget.
All three functions pass a pointer to the XmDrawingAreaCallbackStruct.
Drawing a Line
To draw a line on-screen, use the XDrawLine or XDrawLines function
call. Consider the example shown in Listing 32.16.
Listing 32.16. Drawing lines and points.
/*
** This application shows how to draw lines and points
** by tracking the pointer
*/
#include <X11/Intrinsic.h>
#include <Xm/Xm.h>
#include <Xm/Form.h>
#include <Xm/PushB.h>
#include <Xm/DrawingA.h>
/**
*** used for tracking and drawing via the mouse
**/
static int track;
static int lastx;
static int lasty;
static GC thisGC;
XGCValues gcv;
Widget aForm;
Widget aDraw;
Widget aButton;
/**
*** Connect the mouse down and up movements
**/
void upMouse(Widget w, XtPointer clientdata, XEvent *e, Boolean *f)
{
if (track == 1)
{
XDrawLine(XtDisplay(w),XtWindow(w),
thisGC, lastx, lasty, e->xbutton.x, e->xbutton.y);
}
track = 0;
}
void lostMouse(Widget w, XtPointer clientdata, XEvent *x, Boolean *f)
{
track = 0;
}
/**
*** This function tracks the movement of the mouse by
*** drawing points on its location while a button is
*** pressed.
**/
void moveMouse(Widget w, XtPointer clientdata, XEvent *e, Boolean *f)
{
if (track == 1)
{
printf("\n x: %d, y: %d", e->xmotion.x, e->xmotion.y);
XDrawPoint(XtDisplay(w),XtWindow(w),
thisGC, e->xmotion.x, e->xmotion.y);
}
}
void downMouse(Widget w, XtPointer clientdata, XEvent *e, Boolean *f)
{
track = 1;
lastx = e->xbutton.x;
lasty = e->xbutton.y;
}
void bye(Widget w, XtPointer clientdata, XtPointer calldata);
int main(int argc, char **argv)
{
Widget top;
XtAppContext app;
Arg args[5];
/**
*** Initialize the toolkit.
**/
top = XtAppInitialize(&app, "KBH", NULL, 0, (Cardinal *)&argc,
argv, NULL, args, 0);
/**
*** Create a Form on this top-level Widget. This is a nice Widget
*** to place other Widgets on top of.
**/
aForm = XtVaCreateManagedWidget("Form1",
xmFormWidgetClass, top,
XmNheight,200,
XmNwidth,200,
NULL);
/**
*** Add a button on the form you just created. Note how this Button
*** Widget is connected to the form that it resides on. Only
*** left, right, and bottom edges are attached to the form. The
*** top edge of the button is not connected to the form.
**/
aButton = XtVaCreateManagedWidget("Push to Exit",
xmPushButtonWidgetClass, aForm,
XmNheight,20,
XmNleftAttachment,XmATTACH_FORM,
XmNleftOffset,20,
XmNrightAttachment,XmATTACH_FORM,
XmNrightOffset,20,
XmNbottomAttachment,XmATTACH_FORM,
NULL);
/**
*** Now let's create the label for us.
*** The alignment is set to right-justify the label.
*** Note how the label is attached to the parent form.
**/
aDraw = XtVaCreateManagedWidget("paperusitto",
xmDrawingAreaWidgetClass, aForm,
XmNalignment, XmALIGNMENT_END,
XmNleftAttachment,XmATTACH_FORM,
XmNrightAttachment,XmATTACH_FORM,
XmNtopAttachment,XmATTACH_FORM,
XmNbottomAttachment,XmATTACH_WIDGET,
XmNbottomWidget,aButton,
NULL);
gcv.foreground = BlackPixel(XtDisplay(aDraw), DefaultScreen(XtDisplay(aDraw)));
gcv.background = WhitePixel(XtDisplay(aDraw), DefaultScreen(XtDisplay(aDraw)));
gcv.line_width = 2;
thisGC = XtGetGC( aDraw,
GCForeground | GCBackground | GCLineWidth,
(XGCValues *) &gcv);
/**
*** Now add the event handlers for tracking the mouse on the
*** label. Note that the LeaveWindowMask is set to release
*** the pointer for you should you keep the button pressed
*** and leave the window and disables tracking.
**/
XtAddEventHandler( aDraw, ButtonPressMask, FALSE, downMouse, NULL);
XtAddEventHandler( aDraw, ButtonMotionMask, FALSE, moveMouse, NULL);
XtAddEventHandler( aDraw, ButtonReleaseMask,FALSE, upMouse, NULL);
XtAddEventHandler( aDraw, LeaveWindowMask, FALSE, lostMouse, NULL);
/**
*** Call the function "bye" when the PushButton receives
*** an activate message; i.e. when the pointer is moved to
*** the button and Button1 is pressed and released.
**/
XtAddCallback( aButton, XmNactivateCallback, bye, (XtPointer) NULL);
XtRealizeWidget(top);
XtAppMainLoop(app);
return(0);
}
void reallyQuit(Widget w, XtPointer clientdata, XtPointer calldata)
{
exit(0);
}
/**
*** pesky quit routine
**/
void bye(Widget w, XtPointer clientdata, XtPointer calldata)
{
static Widget quitDlg = NULL;
static char *msgstr = "Are you sure you want to Quit?";
if (quitDlg != (Widget )NULL)
{
/* first time called */
quitDlg = XmCreateQuestionDialog(w,"R U Sure", (XtPointer *)NULL,0);
XtVaSetValues(quitDlg,
XmNdialogStyle, XmDIALOG_FULL_APPLICATION_MODAL,
XtVaTypedArg, XmNmessageString, XmRString,
msgstr,
strlen(msgstr),
NULL);
XtAddCallback(quitDlg, XmNokCallback, reallyQuit, NULL);
}
XtManageChild(quitDlg);
}
The output from Listing 32.16 is shown in Figure 32.12.
Figure 32.12. Drawing points and lines.
This is an example of the primitives required to draw one line on the
Widget. Note the number of GCValues that have to be set to achieve
this purpose. The XDrawLine function definition is as follows:
XDrawLine( Display *dpy,
Drawable d,
GC gc,
int x1,
int y1,
int x2,
int y2);
It's more efficient to draw multiple lines in one call. Use the
XDrawLines function with a pointer to an array of points and its size.
The mode parameter can be set to
* CoorModeOrigin to use the values relative to the drawables'
origin.
* CoorModePrevious to use the values as deltas from the previous
point. A delta is the change in x and y coordinates between this
coordinate and the previous one.
The first point is always relative to the drawables' origin. To draw
boxes, use the XDrawRectangle function:
XDrawRectangle( Display *display, Drawable dwindow,
GC gc,int x,int y,
unsigned int width, unsigned int height);
will draw a rectangle at (x,y) of geometry (width, height). To draw
more than one box at a time, use the XDrawRectangles() function. This
function is declared as
XDrawRectangles( Display *display, Window dwindow,
GC gc, XRectangle *xp, int number);
where xp is a pointer to an array of number rectangle definition
structures.
For filled rectangles, use the XFillRectangle and XFillRectangles
calls, respectively.
Drawing a Point
To draw a point on-screen, use the XDrawPoint or XDrawPoints function
call. This is similar to line-drawing functions. (Refer to Listing
32.16.)
Drawing an Arc
To draw circles, arcs, and similar shapes, use the XDrawArc function:
XDrawArc(Display *display, Window dwindow,
GC gc, int x, int y,
unsigned int width, unsigned int height,
int a1, int a2);
This function is very flexible. It draws an arc from an angle a1
starting from the 3 o'clock position to angle a2. The units for angles
are in one sixty-fourths (1/64) of a degree. The arc is drawn
counterclockwise. The largest value is (64�360) units because the
angle arguments are truncated. The width and height define the
bounding rectangle for the arc. The XDrawArcs() function is used to
draw multiple arcs, given pointers to the array. The prototype for
this function is
XDrawArcs (Display *display, Window dwindow,
GC gc, XArc *arcptr, int number);
To draw polygons, use the call
XDrawSegments( Display *display, Window dwindow, GC gc,
XSegment *segments, int number);
The XSegment structure includes four short members—x1,y1,x2, and
y2—which define the starting and ending points of all segments.
For connected lines, use the XDrawLines function shown earlier. For
filled polygons, use the XFillPolygon() function call.
Using Fonts and FontLists
Fonts are perhaps the trickiest aspect of Motif to master. See the
section on fonts in Chapter 23, "Using Motif," before reading this
section to familiarize yourself with font definitions.
The function XLoadQueryFont(Display *dp, char *name) returns an
XFontStruct structure. This structure defines the extents for the
character set. This is used to set the values of the Font field in a
GC.
To draw a string on the screen, use
XDrawString ( Display *dp, Drawable dw, GC gc,
int x, int y, char *str, int len);
which uses only the foreground color. To draw with the background and
foreground colors, use
XDrawImageString ( Display *dp, Drawable dw, GC gc,
int x, int y, char *str, int len);
The X Color Model
The X Color Model is based on an array of colors called a colormap.
Applications refer to a color by its index into this colormap. The
indices are placed in the application's frame buffer, which contains
an entry for each pixel of the display. The number of bits in the
index defines the number of bitplanes. The number of bitplanes defines
the number of colors that can be displayed on-screen at one time. For
example, one bit per pixel gives two colors, four bits per pixel gives
16 colors, and eight bits per pixel gives 256 colors.
Applications generally inherit the colormap of their parent. They can
also create their own colormap using the XCreateColormap call. The
call is defined as
Colormap XCreateColormap( Display *display, Window dwindow,
Visual *vp, int requested);
This allocates the number of requested color entries in the colormap
for a window. Generally, the visual parameter is derived from the
macro
DefaultVisual (Display *display, int screenNumber);
where screenNumber = 0 in almost all cases. Colormaps are a valuable
resource in X and must be freed after use. This is done via the call
XFreeColormap(Display *display, Colormap c);
Applications can get the standard colormap from the X server by using
the XGetStandardColormap() call, and set it via the
XSetStandardColormap() call. These are defined as
XGetStandardColormap( Display *display, Window dwindow,
XStandardColormap *c, Atom property);
and
XSetStandardColormap( Display *display, Window dwindow,
XStandardColormap *c, Atom property);
Once applications have a Colormap to work with, they have to follow
two steps:
1. Define the colormap entries.
The property atom can take the values of RGB_BEST_MAP,
RGB_GRAY_MAP, or 2RGB_DEFAULT_MAP. These are names of colormaps
stored in the server. They are not colormaps in themselves.
2. Set the colormap for a window via the call
XSetWindowColormap ( Display *display, Window dwindow, Colormap c
);
For setting or allocating a color in the Colormap, use the XColor
structure defined in <X/Xlib.h>.
To see a bright blue color, use the segment
XColor color;
color.red = 0;
color.blue = 0xffff;
color.green = 0;
Then add the color to the Colormap using the call to the function:
XAllocColor(Display *display,
Window dwindow,
XColor *color );
See Listing 32.17 for a sample function to set the color of a Widget.
Listing 32.17. Convenience function for getting colors.
/**
*** Convenience function to get colors
**/
Pixel GetPixel( Widget w, int r, int g, int b)
{
Display *dpy;
int scr;
Colormap cmp;
XColor clr;
dpy = XtDisplay(w);
scr = DefaultScreen(dpy);
cmp = DefaultColormap(dpy);
clr.red = (short)r;
clr.green = (short)g;
clr.blue = (short)b;
clr.flags = DoRed | DoGreen | DoBlue;
/**
*** Note that the default black pixel of the display and screen
*** is returned if the color could not be allocated.
**/
return(XAllocColor(dpy,cmp,&clr) ? clr.pixel : BlackPixel(dpy,scr));
}
The default white and black pixels are defined as
Pixel BlackPixel( Display *dpy, int screen);
Pixel WhitePixel( Display *dpy, int screen);
and will work with any screen as a fallback.
The index (Pixel) returned by this function is not guaranteed to be
the same every time the application runs. This is because the colormap
could be shared between applications requesting colors in different
orders. Each entry is allocated on a next-available-entry basis.
Sometimes, if you overwrite an existing entry in a cell, you might
actually see a change in a completely different application. So be
careful.
Applications can query the RGB components of a color by calling the
function
XQueryColor( Display *display, Colormap *cmp, Xcolor *clr);
For many colors at one time, use
XQueryColors( Display *display, Colormap *cmp,
Xcolor *clr, int number);
At this time the application can modify the RGB components. Then you
can store them in the colormap with the call
XStoreColor( Display *display, Colormap *cmp,XColor *clr);
Recall that X11 has some strange names for colors in the
/usr/lib/rgb.txt file. Applications can get the RGB components of
these names with a call to
XLookupColor( Display *display, Colormap cmp,
char *name,XColor *clr, XColor *exact);
The name is the string to search for in the rgb.txt file. The returned
value clr contains the next closest existing entry in the colormap.
The exact color entry contains the exact RGB definition in the entry
in rgb.txt. This function does not allocate the color in the colormap.
To do that, use the call
XAllocNamedColor( Display *display, Colormap cmp,
char *name, Xcolor *clr, XColor *exact);
Pixmaps, Bitmaps, and Images
A Pixmap is like a window, but is off-screen and therefore invisible
to the user. This is usually the same depth of the screen. You create
a Pixmap with the call
XCreatePixmap (Display *dp,
Drawable dw,
unsigned int width,
unsigned int height,
unsigned int depth);
A drawable can be either a Window (on-screen) or a Pixmap
(off-screen). Bitmaps are Pixmaps of a depth of one pixel. Look in
/usr/include/X11/bitmaps
for a listing of se of the standard bitmaps.
The way to copy Pixmaps from memory to the screen is via the call to
XCopyArea. The prototype for this call is
XCopyArea( Display dp,
Drawable Src, Drawable Dst,
GC gc, int src_x, int src_y,
unsigned int width, unsigned int height,
int dst_x, int dst_y);
The caveat with this XCopyArea is that the depth of the Src and Dst
drawables have to be of the same depth. To show a bitmap on a screen
with depth greater than 1 pixel, you have to copy the bitmap one plane
at a time. This is done via the call
XCopyPlane( Display dp,
Drawable Src, Drawable Dst,
GC gc, int src_x, int src_y,
unsigned int width, unsigned int height,
int dst_x, int dst_y, unsigned long plane);
where the plane specifies the bit plane to which this one-bit-deep
bitmap must be copied. The actual operation is largely dependent on
the modes set in the GC.
For example, to show the files in the /usr/include/bitmaps directory
that have three defined values for a sample file called gumby.h:
* gumby_bits = pointer to an array of character bits.
* gumby_height and gumby_width = integer height and width.
First, create the bitmap from the data using the
XCreateBitmapFromData() call. To display this one-plane-thick image,
copy the image from this plane to plane 1 of the display. You can
actually copy to any plane in the window. A sample call could be set
for copying from your Pixmap to the Widget's plane 1 in the following
manner:
XCopyPlane( XtDisplay(w), yourPixmap, XtWindow(w), gc,
0,0, your_height, your_width, 0,0,1);
where it copies from the origin of the pixmap to the origin of plane 1
of the window.
There are other functions for working with images in X. These include
the capability to store device-dependent images on disk and the Xpm
format.
Summary
This chapter covered the following topics:
* The basics of writing Motif applications
* The special naming conventions in Motif and X
* Writing and compiling your first Motif application
* An overview of the Motif Widget hierarchy
* Working with various common Widgets
* Designing layouts
* Creating pop-up menus and menu bars
* Creating simple dialog boxes
* How to use the mouse in event handling
* How to use colors in X
* How to draw lines and points
This chapter could easily expand into a book. (Please do not tempt
me!) I have only covered the basics of writing Motif applications.
However, given the vast number of tools in Linux, you can see how you
can port any existing Motif application code to and from a Linux
machine. Similarly, a Linux machine can also prove to be a good
development platform for developing Motif applications.
--
Enjoy Linux!
-----It's FREE!-----
※ 修改:．netiscpu 于 Jul 25 05:58:58 修改本文．[FROM: mtlab.hit.edu.cn]
※ 来源:．紫 丁 香 bbs.hit.edu.cn．[FROM: fengyun.hit.edu.]
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