glEdgeFlag (GLboolean flag)表示一个顶点是否应该被认为是多边形的一条边界边的起点。flag为GL_TRUE后面的点都被认为是边界上的点，flag为GL_FALSE则之后的点不是边界上的点。
Demo使用菜单来决定四角星的四个凹进去的点是否是边界边的起点。当菜单选中凹进去的四个点为边界上的点时，使用多边形的填充模式为GL_LINE时如下图所示：
当菜单选中凹进去的四个点不为边界上的点时，使用多边形的填充模式为GL_LINE时如下图所示：
源代码如下所示：
#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;
#define MODE_SOLID 1
#define MODE_LINE 2
#define MODE_POINTS 3
GLint iMode=MODE_SOLID;// 多边形的填充方式
GLboolean bEdgeFlag=GL_TRUE;//控制边的显示与否
//受支持的点大小范围
GLfloat sizes[2];
//受支持的点大小增量
GLfloat step;
//菜单回调函数
void processMenu(int value){
switch(value){
case 1:
iMode=MODE_SOLID;
break;
case 2:
iMode=MODE_LINE;
break;
case 3:
iMode=MODE_POINTS;
break;
case 4:
bEdgeFlag=GL_TRUE;
break;
case 5:
bEdgeFlag=GL_FALSE;
break;
default:
break;
}
//重新绘制
glutPostRedisplay();
}
//显示回调函数
void renderScreen(void){
GLfloat x,y,z,angle;
int i;
//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);
//设置多边形正面和背面的填充模式
if(MODE_SOLID==iMode)
glPolygonMode(GL_FRONT_AND_BACK,GL_FILL);
if(MODE_LINE==iMode)
glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
if(MODE_POINTS==iMode)
glPolygonMode(GL_FRONT_AND_BACK,GL_POINT);
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
if(MODE_POINTS!=iMode){
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();
}
glColor3f(0.0f,1.0f,0.0f);
glBegin(GL_TRIANGLES);
//glPointSize(sizes[1]);
glEdgeFlag(bEdgeFlag);
glVertex2f(-20.0f, 20.0f);
glEdgeFlag(GL_TRUE);
glVertex2f(20.0f, 20.0f);
glVertex2f(0.0f, 60.0f);
glVertex2f(-20.0f,20.0f);
glVertex2f(-60.0f,0.0f);
glEdgeFlag(bEdgeFlag);
glVertex2f(-20.0f,-20.0f);
glEdgeFlag(GL_TRUE);
glVertex2f(-20.0f,-20.0f);
glVertex2f(0.0f, -60.0f);
glEdgeFlag(bEdgeFlag);
glVertex2f(20.0f, -20.0f);
glEdgeFlag(GL_TRUE);
glVertex2f(20.0f, -20.0f);
glVertex2f(60.0f, 0.0f);
glEdgeFlag(bEdgeFlag);
glVertex2f(20.0f, 20.0f);
glEdgeFlag(GL_TRUE);
// Center square as two triangles
glEdgeFlag(bEdgeFlag);
glVertex2f(-20.0f, 20.0f);
glVertex2f(-20.0f,-20.0f);
glVertex2f(20.0f, 20.0f);
glVertex2f(-20.0f,-20.0f);
glVertex2f(20.0f, -20.0f);
glVertex2f(20.0f, 20.0f);
glEdgeFlag(GL_TRUE);
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);
//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
",sizes[0],sizes[1]);
printf("point step:%f
",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<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[])
{
int nModeMenu;
int nEdgeMenu;
int nMainMenu;
//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 Star Demo
glutCreateWindow("OpenGL Star Demo");
//创建二级菜单
nModeMenu=glutCreateMenu(processMenu);
glutAddMenuEntry("Solid",1);
glutAddMenuEntry("Outline",2);
glutAddMenuEntry("Points",3);
nEdgeMenu=glutCreateMenu(processMenu);
glutAddMenuEntry("On",4);
glutAddMenuEntry("Off",5);
nMainMenu=glutCreateMenu(processMenu);
glutAddSubMenu("Mode",nModeMenu);
glutAddSubMenu("Edge",nEdgeMenu);
//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;
}