openGL+VS2010的例程--静态平滑变色三角形（二维）

效果图如上：

步骤：首先，绘制顶点颜色不同的三角形；然后，设置边框大小改变时，重新按固定长宽比例投影，到整个显示界面。

实现代码如下：

#include <GL\glut.h>

void Display(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glBegin(GL_POLYGON);
        glColor3f(0.0,0.0,0.0);
        glVertex3f(-0.5,-0.5,-3.0);
        glColor3f(1.0,0.0,0.0);
        glVertex3f(0.5,-0.5,-3.0);
        glColor3f(0.0,0.0,1.0);
        glVertex3f(0.5,0.5,-3.0);
    glEnd();
    glFlush();            //Finish rendering
}

void Reshape(int x, int y)
{
    if (y == 0 || x == 0) return;  //Nothing is visible then, so return
    //Set a new projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    //Angle of view:40 degrees
    //Near clipping plane distance: 0.5
    //Far clipping plane distance: 20.0
    gluPerspective(40.0,(GLdouble)x/(GLdouble)y,0.5,20.0);
    glMatrixMode(GL_MODELVIEW);
    glViewport(0,0,x,y);  //Use the whole window for rendering
}

int main (int argc, char **argv)
{
    //Initialize GLUT
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(300,300);
    //Create a window with rendering context and everything else we need
    glutCreateWindow("Intro");
    glClearColor(0.0,0.0,0.0,0.0);
    //Assign the two used Msg-routines
    glutDisplayFunc(Display);
    glutReshapeFunc(Reshape);
    //Let GLUT get the msgs
    glutMainLoop();
    return 0;
}