剪裁测试用于限制绘制区域。我们可以指定一个矩形的剪裁窗口，当启用剪裁测试后，只有在这个窗口之内的像素才能被绘制，其它像素则会被丢弃。换句话说，无论怎么绘制，剪裁窗口以外的像素将不会被修改。有的朋友可能玩过《魔兽争霸3》这款游戏。游戏时如果选中一个士兵，则画面下方的一个方框内就会出现该士兵的头像。为了保证该头像无论如何绘制都不会越界而覆盖到外面的像素，就可以使用剪裁测试。可以通过下面的代码来启用或禁用剪裁测试：

glEnable(GL_SCISSOR_TEST);   // 启用剪裁测试glDisable(GL_SCISSOR_TEST); // 禁用剪裁测试

可以通过下面的代码来指定一个位置在(x, y)，宽度为width，高度为height的剪裁窗口。glScissor(x, y, width, height);注意，glScissor窗口坐标是以左下角为(0, 0)，右上角为(width, height)的，这与Windows系统窗口有所不同。

Demo使用裁剪区来将矩形窗口正中间四分之一刷成红色，正中间十六分之一刷成绿色。

源代码：

 

// GlutScissorDemo.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include 
    
     #include 
     
      //圆周率宏#define GL_PI 3.1415f//获取屏幕的宽度GLint SCREEN_WIDTH=0;GLint SCREEN_HEIGHT=0;//设置程序的窗口大小GLint windowWidth=400;GLint windowHeight=300;//绕x轴旋转角度GLfloat xRotAngle=0.0f;//绕y轴旋转角度GLfloat yRotAngle=0.0f;//受支持的点大小范围GLfloat sizes[2];//受支持的点大小增量GLfloat step;//显示回调函数void renderScreen(void){    GLfloat x,y,z,angle;	int i;	// Clear blue window	glClearColor(0.0f, 0.0f, 1.0f, 0.0f);    //把整个窗口清理为当前清理颜色：蓝色    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);    //将当前Matrix状态入栈    glPushMatrix();    //坐标系绕x轴旋转xRotAngle    glRotatef(xRotAngle,1.0f,0.0f,0.0f);    //坐标系绕y轴旋转yRotAngle    glRotatef(yRotAngle,0.0f,1.0f,0.0f);	x=0.0f;	y=0.0f;    z=0.0f;	//进行平滑处理　	glEnable(GL_POINT_SMOOTH);	glHint(GL_POINT_SMOOTH,GL_NICEST);	glEnable(GL_LINE_SMOOTH);	glHint(GL_LINE_SMOOTH,GL_NICEST);	glEnable(GL_POLYGON_SMOOTH);	glHint(GL_POLYGON_SMOOTH,GL_NICEST);	//绘制坐标系	glColor3f(1.0f,1.0f,1.0f);	glBegin(GL_LINES);		glVertex3f(-80.0f,0.0f,0.0f);		glVertex3f(80.0f,0.0f,0.0f);		glVertex3f(0.0f,-80.0f,0.0f);		glVertex3f(0.0f,80.0f,0.0f);		glVertex3f(0.0f,0.0f,-80.0f);		glVertex3f(0.0f,0.0f,80.0f);	glEnd();	glPushMatrix();	glTranslatef(80.0f,0.0f,0.0f);	glRotatef(90.0f,0.0f,1.0f,0.0f);	glutWireCone(3,6,10,10);	glPopMatrix();	glPushMatrix();	glTranslatef(0.0f,80.0f,0.0f);	glRotatef(-90.0f,1.0f,0.0f,0.0f);	glutWireCone(3,6,10,10);	glPopMatrix();	glPushMatrix();	glTranslatef(0.0f,0.0f,80.0f);	glRotatef(90.0f,0.0f,0.0f,1.0f);	glutWireCone(3,6,10,10);	glPopMatrix();	    //使能裁剪区	glEnable(GL_SCISSOR_TEST);	//将窗口中间的四分之一面积清空为红色    glClearColor(1.0f, 0.0f, 0.0f, 0.0f);    glScissor(windowWidth/4,windowHeight/4, windowWidth/2,windowHeight/2);    glClear(GL_COLOR_BUFFER_BIT);        //将窗口中间的十六分之一面积清空为绿色    glClearColor(0.0f, 1.0f, 0.0f, 0.0f);    glScissor(windowWidth*3/8,windowHeight*3/8, windowWidth/4,windowHeight/4);    glClear(GL_COLOR_BUFFER_BIT);        //禁止裁剪区    glDisable(GL_SCISSOR_TEST);	    //恢复压入栈的Matrix    glPopMatrix();    //交换两个缓冲区的指针    glutSwapBuffers();}//设置Redering State void setupRederingState(void){    //设置清理颜色为黑色    glClearColor(0.0f,0.0,0.0,1.0f);    //设置绘画颜色为绿色    glColor3f(0.0f,1.0f,0.0f);	//使能深度测试	glEnable(GL_DEPTH_TEST);	//获取受支持的点大小范围	glGetFloatv(GL_POINT_SIZE_RANGE,sizes);	//获取受支持的点大小增量	glGetFloatv(GL_POINT_SIZE_GRANULARITY,&step);	printf("point size range:%f-%f\n",sizes[0],sizes[1]);	printf("point step:%f\n",step);}//窗口大小变化回调函数void changSize(GLint w,GLint h){    //横宽比率    GLfloat ratio;    //设置坐标系为x(-100.0f,100.0f)、y(-100.0f,100.0f)、z(-100.0f,100.0f)    GLfloat coordinatesize=100.0f;    //窗口宽高为零直接返回    if((w==0)||(h==0))        return;    //设置视口和窗口大小一致    glViewport(0,0,w,h);    //对投影矩阵应用随后的矩阵操作    glMatrixMode(GL_PROJECTION);    //重置当前指定的矩阵为单位矩阵　    glLoadIdentity();    ratio=(GLfloat)w/(GLfloat)h;    //正交投影    if(w