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 else glDisable(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 else glDisable(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 else glPolygonMode(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; }