OpenGL simulates the process of a ball falling to the ground and bouncing up in real life. Draw a ball on the screen, and the ball will fall from top to bottom, hit the ground and bounce up again.

// Simulate real life , The process of the ball falling to the ground and bouncing up , Draw a ball on the screen , The ball fell from the top , Hit the ground , Play again .
#define GLUT_DISABLE_ATEXIT_HACK
#include <gl/glut.h>
float y=1.5f;
float dy=-0.4f;

// initialization OpenGL
void DrawCube()
{

	// Set the clear screen color to black 
	glClearColor(0.0f,0.0f,0.0f,0.0f);
	// Clear color buffer and depth buffer 
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);			

	glPushMatrix();
	glTranslatef(0.0f,y,0.0f);
	glColor3f(1.0f,0.5f,0.5f);
    glutSolidSphere(1.0,50,10);                          
	glPopMatrix();
}
void init(void) 
{
	glClearColor(0.0f, 0.0f, 0.0f, 0.5f);						
	glClearDepth(1.0f);											
	glDepthFunc(GL_LEQUAL);										
	glEnable(GL_DEPTH_TEST);
	glShadeModel(GL_FLAT);				
}
// The main drawing process 
void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT);// Clear color cache     
	glLoadIdentity();	
	glTranslatef(0,0,-5);
	glColor3f(1.0,0,0);
	DrawCube();	
    glFlush();
}
// Call when the window changes size 
void reshape(int w, int h){
	glViewport(0, 0, w, h);// Set up the viewport 
	glMatrixMode(GL_PROJECTION);// Set the current projection transformation mode 
	glLoadIdentity();// Replace the current transformation matrix with the identity matrix 
	gluPerspective(100, (float)w/h, 3, 100.0);// Set the orthographic projection body 
	glMatrixMode (GL_MODELVIEW);
	glLoadIdentity();
}

void TimerFunction(int value)
{	
	y+=dy;
	if(y<=-2||y>=3.5)
		dy=-dy;
	glutTimerFunc(100,TimerFunction, 1);
	// Redraw the scene with new coordinates
    glutPostRedisplay();
	
}

void main( )
{	
	glutCreateWindow("2");// Set the window title 
	init();// initialization OpenGL
	glutDisplayFunc(display);// Set display callback function  
	glutReshapeFunc(reshape);// Set up reshape Callback function 
	glutTimerFunc(100,TimerFunction, 1);
	glutMainLoop();// Enter the main loop 	
}