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发信人: dht (bbs), 信区: Graphics
标  题: OPENGL(12)
发信站: 紫丁香 (Sun Oct  4 21:50:11 1998), 转信

此次讲解OPENGL复杂建模方式，将分几个部分完成，这篇先介绍图原扩展：
如何利用专用函数精确绘制平面图形。下次会讲解如何利用法向量生成曲面。
1.点和线
void glPointSize(GLfloat size);
设置点的宽度，size必须>0，缺省1

void glLineWidth(GLfoat width);
设置线宽，width>0，缺省为1

void glLineStipple(GLint factor,GLushort pattern);
设置线的模式，factor用于对模式进行拉伸的比例因子，pattern是线的模式
例如11001100是虚线（1绘制，0不绘制）

必须要启用glEnable(GL_LINE_STIPPLE)才能使用以上函数，不再使用时调用
glDisable(GL_LINE_STIPPLE)关闭，这与以前的glEnable();glDisable();的
用法都是类似的。请看下面例子：
///////////////////////////////////////////////////////////////////
//sample.cpp
#include "glos.h"
#include <GL/gl.h>
#include <GL/glaux.h>
#include "windows.h"
void myinit(void);
void CALLBACK  display(void);
void CALLBACK  reshape(GLsizei w,GLsizei h);

void myinit(void)
{
        auxInitDisplayMode(AUX_SINGLE|AUX_RGBA);
        auxInitPosition(0,0,600,500);
        auxInitWindow("sample1");
        glClearColor(0.0,0.0,0.0,0.0);
        glClear(GL_COLOR_BUFFER_BIT);

        glShadeModel(GL_FLAT);
}
/*
void CALLBACK reshape(GLsizei w,GLsizei h)
{

glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();

if(w<=h)
glOrtho(-4.0,4.0,-4.0*(GLfloat)h/(GLfloat)w,
         4.0*(GLfloat)h/(GLfloat)w,-4.0,4.0);
else
  glOrtho(-4.0*(GLfloat)h/(GLfloat)w,
         4.0*(GLfloat)h/(GLfloat)w,-4.0,4.0,-4.0,4.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
*/

//自定义的绘制直线的函数，参数为起始点和终止点坐标
void line2i(GLint x1,GLint y1,GLint x2,GLint y2)
{
glBegin(GL_LINES);
glVertex2f(x1,y1);
glVertex2f(x2,y2);
glEnd();
}

void CALLBACK display(void)
{
  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

//首先绘制一系列点，点的大小不断增加
  int i;
  glColor3f(0.8,0.6,0.4);
  for(i=1;i<=10;i++)
  {
          glPointSize(i*2);
          glBegin(GL_POINTS);
          glVertex2f(30.0+((GLfloat)i*50.0),330.0);
          glEnd();
  }
//再绘制两条虚线，第二条比第一条松散一些，由pattern参数即可看出
  glEnable(GL_LINE_STIPPLE);
  glLineStipple(1,0x0101);//间隔1位
  glColor3f(1.0,0.0,0.0);
  line2i(20,250,250,250);
  glLineStipple(1,0x00ff);//间隔2位
  glColor3f(0.0,0.0,1.0);
  line2i(300,250,550,250);

//改变线的绘制宽度的效果--加宽
//重新画出上面两条虚线
  glLineWidth(5.0);
  glEnable(GL_LINE_STIPPLE);
  glLineStipple(1,0x0101);
  glColor3f(1.0,0.0,0.0);
  line2i(50,150,250,150);
  glLineStipple(1,0x00ff);
  glColor3f(0.0,0.0,1.0);
  line2i(300,150,550,150);

  glFlush();
}
void main(void)
{
        myinit();

//    auxReshapeFunc(reshape);
    auxMainLoop(display);
}
//end of sample
//////////////////////////////////////////////

2.多边形
void glPolygonMode(GLenum face,GLenum mode);
控制多边形指定面的绘图模式，
face为：GL_FRONT GL_BACK或GL_FRONT_AND BACK
mode为：GL_POINT GL_LINE或GL_FILL表示多边型的轮廓点、轮廓线和填充模式
的绘制方式。缺省是填充方式。

void glPolygonStipple(const GLubyte *mask);
其中mask必须是指向32*32的位图指针，1是绘制、0不绘制

使用上述函数也要调用：
glEnable(GL_POLYGON-STIPPLE);
glDisable(GL_POLYGON_STIPPLE);
请看下面例子：
/////////////////////////////////////////////
//sample.cpp
#include "glos.h"
#include <GL/gl.h>
#include <GL/glaux.h>
#include "windows.h"
void myinit(void);
void CALLBACK  display(void);
void CALLBACK  reshape(GLsizei w,GLsizei h);

//定义填充模式32*32点阵
GLubyte pattern[]={
        0x00,0x01,0x80,0x00,
        0x00,0x03,0xc0,0x00,
        0x00,0x07,0xe0,0x00,
        0x00,0x0f,0xf0,0x00,
        0x00,0x1f,0xf8,0x00,
        0x00,0x3f,0xfc,0x00,
        0x00,0x7f,0xfe,0x00,
        0x00,0xff,0xff,0x00,
        0x01,0xff,0xff,0x80,
        0x03,0xff,0xff,0xc0,
        0x07,0xff,0xff,0xe0,
        0x0f,0xff,0xff,0xf0,
        0x1f,0xff,0xff,0xf8,
        0x3f,0xff,0xff,0xfc,
        0x7f,0xff,0xff,0xfe,
        0xff,0xff,0xff,0xff,

        0xff,0xff,0xff,0xff,
        0x7f,0xff,0xff,0xfe,
        0x3f,0xff,0xff,0xfc,
        0x1f,0xff,0xff,0xf8,
        0x0f,0xff,0xff,0xf0,
        0x07,0xff,0xff,0xe0,
        0x03,0xff,0xff,0xc0,
        0x01,0xff,0xff,0x80,
        0x00,0xff,0xff,0x00,
        0x00,0x7f,0xfe,0x00,
        0x00,0x3f,0xfc,0x00,
        0x00,0x1f,0xf8,0x00,
        0x00,0x0f,0xf0,0x00,
        0x00,0x07,0xe0,0x00,
        0x00,0x03,0xc0,0x00,
        0x00,0x01,0x80,0x00
};

void myinit(void)
{
    auxInitDisplayMode(AUX_SINGLE|AUX_RGBA);
        auxInitPosition(0,0,400,400);
        auxInitWindow("sample1");
        glClearColor(0.0,0.0,0.0,0.0);
        glClear(GL_COLOR_BUFFER_BIT);

        glShadeModel(GL_FLAT);
}
/*
void CALLBACK reshape(GLsizei w,GLsizei h)
{

glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();

if(w<=h)
glOrtho(-4.0,4.0,-4.0*(GLfloat)h/(GLfloat)w,
         4.0*(GLfloat)h/(GLfloat)w,-4.0,4.0);
else
  glOrtho(-4.0*(GLfloat)h/(GLfloat)w,
         4.0*(GLfloat)h/(GLfloat)w,-4.0,4.0,-4.0,4.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
*/

void CALLBACK display(void)
{
  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
//选用兰色作为填充色
  glColor3f(0.0,0.0,1.0);
//启用多边形绘制模式
  glEnable(GL_POLYGON_STIPPLE);
//利用定义好的填充模式绘制多边形
  glPolygonStipple(pattern);
//绘制长方形
  glRectf(48.0,80.0,210.0,305.0);

  glFlush();
}
void main(void)
{
        myinit();

//    auxReshapeFunc(reshape);
    auxMainLoop(display);
}
//end of sample
例子中的运行结果是给出一个表面有定义图样的长方形

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※ 来源:．紫丁香 bbs.hit.edu.cn．[FROM: cadcam.hit.edu.c]

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