VS2012下基於Glut OpenGL連續點圍成曲面正面與背面示例程序：

OpenGL下連續點圍成的曲面，當連續點是逆時針時圍成的曲面是正面，反之則是反面。下面的程序來測試是不是這樣。

我們的程序在曲面是正面時使用顏色填充，背面時使用曲線描輪廓。按鍵盤的UP，DOWN，LEFT，RIGHT按鍵可以從不同角度查看該圖形。

源代碼如下所示：

// GlutBackAndFrontDemo.cpp : 定義控制檯應用程序的入口點。
//

#include "stdafx.h"
#include <gl/glut.h>
#include <math.h>
//圓周率宏
#define GL_PI 3.1415f
//獲取屏幕的寬度
GLint SCREEN_WIDTH=0;
GLint SCREEN_HEIGHT=0;
//設置程序的窗口大小
GLint windowWidth=400;
GLint windowHeight=300;
//繞x軸旋轉角度
GLfloat xRotAngle=0.0f;
//繞y軸旋轉角度
GLfloat yRotAngle=0.0f;
//顯示回調函數
void renderScreen(void){
    GLfloat x,y,z,angle;
    //把整個窗口清理爲當前清理顏色：黑色
    glClear(GL_COLOR_BUFFER_BIT);
    //將當前Matrix狀態入棧
    glPushMatrix();
    //座標系繞x軸旋轉xRotAngle
    glRotatef(xRotAngle,1.0f,0.0f,0.0f);
    //座標系繞y軸旋轉yRotAngle
    glRotatef(yRotAngle,0.0f,1.0f,0.0f);

	//進行平滑處理　
	glEnable(GL_POINT_SMOOTH);
	glHint(GL_POINT_SMOOTH,GL_NICEST);
	glEnable(GL_LINE_SMOOTH);
	glHint(GL_LINE_SMOOTH,GL_NICEST);
	//使用白色繪製座標系
	glColor3f(1.0f,1.0f,1.0f);
	//繪製座標系
	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();



	//座標系平移到(-20.0f,0.0f,00.0f)
	glPushMatrix();
	glTranslatef(-20.0f,0.0f,00.0f);
	//GL_FLAT使用單色模式填充三角形 
	//GL_SMOOTH使用顏色平滑變換模式填充三角形 
	glShadeModel(GL_FLAT);
	//使用GL_TRIANGLE_STRIP繪製三角形
	glBegin(GL_TRIANGLE_STRIP);
		//使用紅色繪製第一個逆時針三角形
		glColor3f(1.0f,0.0f,0.0f);
		glVertex3f(0.0f,0.0f,0.0f);
		glVertex3f(-25.0f,25.0f,0.0f);
		glVertex3f(-50.0f,0.0f,0.0f);
	//結束GL_TRIANGLE_STRIP繪製三角形
	glEnd();
	glPopMatrix();
	
	//座標系平移到(20.0f,0.0f,00.0f)
	glPushMatrix();
	glTranslatef(20.0f,0.0f,00.0f);
	//GL_FLAT使用單色模式填充三角形 
	//GL_SMOOTH使用顏色平滑變換模式填充三角形 
	glShadeModel(GL_SMOOTH);
	//使用GL_TRIANGLE_STRIP繪製三角形
	glBegin(GL_TRIANGLE_STRIP);
		//使用藍色繪製第一個順時針三角形
		glColor3f(0.0f,0.0f,1.0f);
		glVertex3f(0.0f,0.0f,0.0f);
		glVertex3f(25.0f,25.0f,0.0f);
		glVertex3f(50.0f,0.0f,0.0f);
	//結束GL_TRIANGLE_STRIP繪製三角形
	glEnd();
	glPopMatrix();
	

	
    //恢復壓入棧的Matrix
    glPopMatrix();
    //交換兩個緩衝區的指針
    glutSwapBuffers();
}
//設置Redering State 
void setupRederingState(void){
    //設置清理顏色爲黑色
    glClearColor(0.0f,0.0,0.0,1.0f);
    //設置繪畫顏色爲綠色
    glColor3f(0.0f,1.0f,0.0f);
	//多邊形背面使用線條填充
	glPolygonMode(GL_BACK,GL_LINE);
	//改變正背面
	//glFrontFace(GL_CW);
}
//窗口大小變化回調函數
void changSize(GLint w,GLint h){
    //橫寬比率
    GLfloat ratio;
    //設置座標系爲x(-100.0f,100.0f)、y(-100.0f,100.0f)、z(-100.0f,100.0f)
    GLfloat coordinatesize=100.0f;
    //窗口寬高爲零直接返回
    if((w==0)||(h==0))
        return;
    //設置視口和窗口大小一致
    glViewport(0,0,w,h);
    //對投影矩陣應用隨後的矩陣操作
    glMatrixMode(GL_PROJECTION);
    //重置當前指定的矩陣爲單位矩陣　
    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);
    //對模型視圖矩陣堆棧應用隨後的矩陣操作
    glMatrixMode(GL_MODELVIEW);
    //重置當前指定的矩陣爲單位矩陣　
    glLoadIdentity();
}

//按鍵輸入處理回調函數
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;
    }
    //重新繪製
    glutPostRedisplay();
}

int main(int argc, char* argv[])
{
    //初始化glut 
    glutInit(&argc,argv);
    //使用雙緩衝區模式
    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA|GLUT_DEPTH);
    //獲取系統的寬像素
    SCREEN_WIDTH=glutGet(GLUT_SCREEN_WIDTH);
    //獲取系統的高像素
    SCREEN_HEIGHT=glutGet(GLUT_SCREEN_HEIGHT);
	//創建窗口，窗口名字爲OpenGL BackAndFront Demo
    glutCreateWindow("OpenGL BackAndFront Demo");
    //設置窗口大小
    glutReshapeWindow(windowWidth,windowHeight);
    //窗口居中顯示
    glutPositionWindow((SCREEN_WIDTH-windowWidth)/2,(SCREEN_HEIGHT-windowHeight)/2);
    //窗口大小變化時的處理函數
    glutReshapeFunc(changSize);
    //設置顯示回調函數 
    glutDisplayFunc(renderScreen);
    //設置按鍵輸入處理回調函數
    glutSpecialFunc(specialKey);
    //設置全局渲染參數
    setupRederingState();
    glutMainLoop();
    return 0;
}