VS2012下基于Glut OpenGL GL_POLYGON示例程序：

很多书介绍 GL_POLYGON连续点生成多边形时这下点必须是凸多边形的，规则如下图所示。写个Demo验证了下似乎不是凸多边形的也可以。

Demo的正面与背面显示效果：

源代码如下所示：

// GlutPolygonDemo.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <gl/glut.h>#include <math.h>//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;//是否打开不显示背面功能GLint cullFace=0;//是否打开深度测试功能GLint depthTest=0;//背面是采用线条描外框还是使用单色填充　GLint outLine=0;//菜单回调函数void processMenu(int value){switch(value){case 1:depthTest=!depthTest;break;case 2:cullFace=!cullFace;case 3:outLine=!outLine;break;break;default:break;}//重新绘制glutPostRedisplay();}//显示回调函数void renderScreen(void){    GLfloat x,y,z,angle;    //把整个窗口清理为当前清理颜色：黑色    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);if(depthTest)glEnable(GL_DEPTH_TEST);//打开深度测试功能elseglDisable(GL_DEPTH_TEST);//关闭深度测试功能if(cullFace)glEnable(GL_CULL_FACE);//打开不显示背面功能elseglDisable(GL_CULL_FACE);//关闭不显示背面功能if(outLine)glPolygonMode(GL_BACK,GL_LINE);//多边形背部使用线条描框elseglPolygonMode(GL_BACK,GL_FILL);//多边形背部使用单色填充x=0.0f;y=0.0f;    z=0.0f;//进行平滑处理　glEnable(GL_LINE_SMOOTH);glHint(GL_LINE_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();//开始绘制两个三角形glBegin(GL_POLYGON);//红色绘制第一个四边形glColor3f(1.0f,0.0f,0.0f);glVertex3f(0.0f,0.0f,0.0f);glVertex3f(0.0f,50.0f,0.0f);glVertex3f(25.0f,5.0f,0.0f);glVertex3f(5.0f,25.0f,0.0f);glVertex3f(50.0f,0.0f,0.0f);    //结束绘三角形    glEnd();    //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);}//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<h)        glOrtho(-coordinatesize,coordinatesize,-coordinatesize/ratio,coordinatesize/ratio,-coordinatesize,coordinatesize);    else        glOrtho(-coordinatesize*ratio,coordinatesize*ratio,-coordinatesize,coordinatesize,-coordinatesize,coordinatesize);    //对模型视图矩阵堆栈应用随后的矩阵操作    glMatrixMode(GL_MODELVIEW);    //重置当前指定的矩阵为单位矩阵　    glLoadIdentity();}//按键输入处理回调函数void specialKey(int key,int x,int y){    if(key==GLUT_KEY_UP){        xRotAngle-=5.0f;    }    else if(key==GLUT_KEY_DOWN){        xRotAngle+=5.0f;    }    else if(key==GLUT_KEY_LEFT){        yRotAngle-=5.0f;    }    else if(key==GLUT_KEY_RIGHT){        yRotAngle+=5.0f;    }    //重新绘制    glutPostRedisplay();}int main(int argc, char* argv[]){    //初始化glut     glutInit(&argc,argv);    //使用双缓冲区模式    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA|GLUT_DEPTH);    //获取系统的宽像素    SCREEN_WIDTH=glutGet(GLUT_SCREEN_WIDTH);    //获取系统的高像素    SCREEN_HEIGHT=glutGet(GLUT_SCREEN_HEIGHT);//创建窗口，窗口名字为OpenGL TriAngle Demo    glutCreateWindow("OpenGL Polygon Demo");//菜单回调函数glutCreateMenu(processMenu);//添加菜单glutAddMenuEntry("Toggle depth test",1);glutAddMenuEntry("Toggle cull face",2);glutAddMenuEntry("Toggle back outline",3);//将菜单榜定到鼠标右键上glutAttachMenu(GLUT_RIGHT_BUTTON);    //设置窗口大小    glutReshapeWindow(windowWidth,windowHeight);    //窗口居中显示    glutPositionWindow((SCREEN_WIDTH-windowWidth)/2,(SCREEN_HEIGHT-windowHeight)/2);    //窗口大小变化时的处理函数    glutReshapeFunc(changSize);    //设置显示回调函数     glutDisplayFunc(renderScreen);    //设置按键输入处理回调函数    glutSpecialFunc(specialKey);    //设置全局渲染参数    setupRederingState();    glutMainLoop();    return 0;}