《OpenGL超级宝典》反弹的正方形动画 出不来？！

[ronal7do]

#include <windows.h>
#include <stdio.h>
#define GLUT_DISABLE_ATEXIT_HACK
#include <GL/glut.h>
#include <GL/gl.h>
#include <GL/glu.h>

GLfloat x1 = 100.0f;
GLfloat y10 = 150.0f;
GLsizei rsize = 50;
GLfloat xstep = 1.0f;
GLfloat ystep = 1.0f;
GLfloat windowWidth;
GLfloat windowHeight;

void init()
{
    glClearColor(0.0f,1.0f,1.0f,1.0f);
}
void RenderScene()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0f,1.0f,0.0f);
    glRectf(x1,y10,x1 + rsize,y10 + rsize);
    glutSwapBuffers();
}
void TimerFunction(int value)
{
    if(x1 > windowWidth - rsize||x1 < 0)
        xstep = -xstep;
    if(y10 > windowHeight - rsize||y10 < 0)
        ystep = -ystep;
    if(x1 > windowWidth - rsize)
        x1 = windowWidth - rsize - 1;
    if(y10 > windowHeight - rsize)
        y10 = windowHeight - rsize - 1;
    x1 += xstep;
    y10 += ystep;
    
    glutPostRedisplay();
    glutTimerFunc(33,TimerFunction,1);
}

void ChangeSize(GLsizei w,GLsizei h)
{
    if(h == 0)
        h = 1;
    glViewport(0,0,w,h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if(w <= h)
        glOrtho(0.0f,250.0f,0.0f,250.0f * h / w,1.0f,-1.0f);
    else
        glOrtho(0.0f,250.0f * w / h,0.0f,250.0f,1.0f,-1.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
void main()
{
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowPosition(100,0);//屏幕左上角为原点（0,0）
    glutInitWindowSize(600,600);
    glutCreateWindow("test");
    glutDisplayFunc(RenderScene);
    glutReshapeFunc(ChangeSize);
    glutTimerFunc(33,TimerFunction,1);
    init();
    glutMainLoop();
}

入体，程序是教程上面的，不知道为啥就是出不来动画。大家帮忙看看，谢谢。