在窗体上绘制一个矩形，just a demo

#include 
     
      void init(){    glClearColor(0.0,0.0,0.0,0.0);    glShadeModel(GL_FLAT);} void display(){    glClear(GL_COLOR_BUFFER_BIT);    glColor3f(1.0,1.0,1.0);    glLoadIdentity();    gluLookAt(0.0,0.0, 5.0, 0.0,0.0,0.0,0.0,1.0,0.0);    glScalef(1.0,2.0,1.0);    glutWireCube(1.0);    glFlush();} void reshape(int w,int h){    glViewport(0, 0, (GLsizei)w, (GLsizei)h);    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    glFrustum(-1, 1.0, -1, 1.0, 1.5, 20.0);    glMatrixMode(GL_MODELVIEW);} int main(int argc, char ** argv){    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);    glutInitWindowSize(500, 500);    glutInitWindowPosition(100,100);    glutCreateWindow("Xcode Glut Demo");    init();    glutDisplayFunc(display);    glutReshapeFunc(reshape);    glutMainLoop();    return 0;}