/*
 *  pong.c
 *  This is a simple double buffered program.
 *  Use the left and right arrow keys to move the paddle.
 *  Use the home key to re-center the paddle and return the ball "home."
 *  The beginnings of the classic video game.
 */


#include <GL/glut.h>
#include <stdlib.h>


GLdouble paddleX = 0.0;
GLdouble paddleDelta = 1.0;

GLdouble ballX = 0.0;
GLdouble ballY = 0.0;
GLdouble ballXDelta = 0.5;
GLdouble ballYDelta = 0.5;

GLuint ball;


void display(void)
{
   glClear(GL_COLOR_BUFFER_BIT);

   // Render paddle.
   glColor3f(1.0, 1.0, 1.0);
   glBegin(GL_QUADS);
		glVertex2d(paddleX - 10.0, -50.0);
		glVertex2d(paddleX - 10.0, -45.0);
		glVertex2d(paddleX + 10.0, -45.0);
		glVertex2d(paddleX + 10.0, -50.0);
   glEnd();

   // Render ball.
   glColor3f(1.0, 0.0, 0.0);
   glPushMatrix();
   glTranslatef(ballX, ballY, 0.0);
   glCallList(ball);
   glPopMatrix();
   
   glutSwapBuffers();
}


void init(void) 
{
   GLUquadricObj *qobj;

   glClearColor (0.0, 0.0, 0.0, 0.0);
   glShadeModel (GL_FLAT);   // Probably unnecessary.

   // Create the ball.
   ball = glGenLists(1);
   qobj = gluNewQuadric();
   glNewList(ball, GL_COMPILE);
		gluDisk(qobj, 0.0, 5.0, 72, 1);
   glEndList();
}


void reshape(int w, int h)
{
   // Probably needs to be fixed.

   glViewport (0, 0, (GLsizei) w, (GLsizei) h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(-50.0, 50.0, -50.0, 50.0, -1.0, 1.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}


void keyboard(int key, int x, int y)
{
   // Limited here by keyboard repeat rate.

	switch (key)
	{
	case GLUT_KEY_LEFT:
		paddleX -= paddleDelta;
		break;

	case GLUT_KEY_RIGHT:
		paddleX += paddleDelta;
		break;

	case GLUT_KEY_HOME:
		paddleX = 0.0;
		ballX = ballY = 0.0;
		break;
	}
	glutPostRedisplay();
}


void idle(void)
{
	ballX += ballXDelta;
	ballY += ballYDelta;
	glutPostRedisplay();
}

   
/* 
 *  Request double buffer display mode.
 *  Register "special" input callback functions for arrow and home keys.
 */

int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
   glutInitWindowSize (250, 250); 
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init ();
   glutDisplayFunc(display); 
   glutReshapeFunc(reshape); 
   glutSpecialFunc(keyboard);
   glutIdleFunc(idle);
   glutMainLoop();
   return 0;   /* ANSI C requires main to return int. */
}