Rebote de Pelota

#include <gl/glut.h>
#include <Math.h>    
#define PI 3.14159265f
     
char title[] = "Rebote de Pelota"; 
int windowWidth  = 640;    
int windowHeight = 480;    
int windowPosX   = 50;     
int windowPosY   = 50;     
  
GLfloat ballRadius = 0.2f;  
GLfloat xPos = 0.0f;        
GLfloat yPos = 0.0f;
GLfloat xPosMax, xPosMin, yPosMax, yPosMin;
GLdouble xLeft, xRight, yBottom, yTop;    
GLfloat xSpeed = 0.02f;     
GLfloat ySpeed = 0.007f;
int refreshMillis = 10;     
     
void initGL() {
   glClearColor(0.0, 1.0, 0.0, 0.0);
}
 
void display() {
   glClear(GL_COLOR_BUFFER_BIT);
 
   glLoadIdentity();              
   glTranslatef(xPos, yPos, 0.0f); 

   glBegin(GL_TRIANGLE_FAN);
      glColor3f(0.0f, 0.0f, 1.0f);
      glVertex2f(0.0f, 0.0f);      
      int numSegments = 100;
      GLfloat angle;
      for (int i = 0; i <= numSegments; i++) {
         angle = i * 2.0f * PI / numSegments; 
         glVertex2f(cos(angle) * ballRadius, sin(angle) * ballRadius);
      }
   glEnd();
  
   glutSwapBuffers(); 
  
 
   xPos += xSpeed;
   yPos += ySpeed;
  
   if (xPos > xPosMax) {
      xPos = xPosMax;
      xSpeed = -xSpeed;
   } else if (xPos < xPosMin) {
      xPos = xPosMin;
      xSpeed = -xSpeed;
   }
   if (yPos > yPosMax) {
      yPos = yPosMax;
      ySpeed = -ySpeed;
   } else if (yPos < yPosMin) {
      yPos = yPosMin;
      ySpeed = -ySpeed;
   }
}
 
void reshape(GLsizei weight, GLsizei height) {
   if (height == 0) height = 1;             
   GLfloat aspect = (GLfloat)weight / height;
  
   glViewport(0, 0, weight, height);
  
  
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();           
   if (weight <= height) {
      xLeft   = -1.0;
      xRight  = 1.0;
      yBottom = -1.0 / aspect;
      yTop    = 1.0 / aspect;
   } else {
      xLeft   = -1.0 * aspect;
      xRight  = 1.0 * aspect;
      yBottom = -1.0;
      yTop    = 1.0;
   }
   gluOrtho2D(xLeft, xRight, yBottom, yTop);
 
  
   yPosMin = yBottom + ballRadius;
   yPosMax = yTop - ballRadius;
  
  
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();          
}
 
void Timer(int value) {
 glutPostRedisplay();  
 glutTimerFunc(refreshMillis, Timer, 0);
}
  
int main(int argc, char** argv) {
   glutInit(&argc, argv);           
   glutInitDisplayMode(GLUT_DOUBLE);
   glutInitWindowSize(windowWidth, windowHeight); 
   glutInitWindowPosition(windowPosX, windowPosY);
   glutCreateWindow(title);     
   glutDisplayFunc(display);  
   glutReshapeFunc(reshape);  
   glutTimerFunc(0, Timer, 0);  
   initGL();                    
   glutMainLoop();             
   return 0;
}