OpenGL碰到边界返回的方块

下期预告：Android的OpenGL ES版的碰到边界返回的方块

#include <GL/glut.h>

// 方块的初始位置和大小
GLfloat x1 = 0.0f;
GLfloat y1 = 0.0f;
GLfloat rsize = 25;

// 在x和y方向上的步进大小
GLfloat xstep = 1.0f;
GLfloat ystep = 1.0f;

// 追踪窗口的宽度和高度的变化
GLfloat windowWidth;
GLfloat windowHeight;

void ChangeSize(GLsizei w, GLsizei h)
{
    GLfloat aspectRatio;

    // 防止被0除
    if(h == 0)
    {
        h = 1;
    }

    glViewport(0, 0, w, h);

    // 重置坐标系统
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    aspectRatio = (GLfloat) w / (GLfloat) h;
    if(w <= h)
    {
        windowWidth = 200;
        windowHeight = 200 / aspectRatio;
        glOrtho(-100.0, 100.0, -100 / aspectRatio, 100 / aspectRatio, 1.0, -1.0);
    }
    else
    {
        windowHeight = 200;
        windowWidth = 200 * aspectRatio;
        glOrtho(-100.0 * aspectRatio, 100.0 * aspectRatio, -100, 100, 1.0, -1.0);
    }

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void SetupRC()
{
    glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
}

void RenderScene()
{
    // 用当前的清除颜色清除窗口
    glClear(GL_COLOR_BUFFER_BIT);
    // 把绘图颜色设置为红色
    glColor3f(1.0f, 0.0f, 0.0f);
    glRectf(x1, y1, x1 + rsize, y1 - rsize);
    glutSwapBuffers();
}

void TimerFunction(int value)
{
    // 到达边界时翻转方块的方向
    if(x1 > windowWidth / 2 - rsize || x1 < - windowWidth / 2)
    {
        xstep = -xstep;
    }

    if(y1 > windowHeight / 2 || y1 < - windowHeight / 2 - rsize)
    {
        ystep = -ystep;
    }

    // 移动方块
    x1 += xstep;
    y1 += ystep;

    glutPostRedisplay();
    glutTimerFunc(33, TimerFunction, 1);
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(800, 600);
    glutCreateWindow("GLUT Example!!!");
    glutDisplayFunc(RenderScene);
    glutReshapeFunc(ChangeSize);
    glutTimerFunc(33, TimerFunction, 1);
    SetupRC();

    glutMainLoop();
    return 0;
}