#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include <unistd.h>
#include <math.h>
#include <time.h>

#define  WIN_SIZE   600
#define  SPEED      10
#define  RADIUS     15
#define  PI         3.14159


int main() {
  Display *display;
  Window   win;
  GC       gc;
  
  int      x = WIN_SIZE/2, y = WIN_SIZE/2;
  float    direction;
  
  
  // Opens connection to X server
  display = XOpenDisplay(NULL);

  // Create a simple window, set the title and get the graphics context then
  // make is visible and get ready to draw
  win = XCreateSimpleWindow(display,  RootWindow(display, 0), 0, 0,
			    WIN_SIZE, WIN_SIZE, 0, 0x000000, 0xFFFFFF);
  XStoreName(display, win, "Bouncing Ball");
  gc = XCreateGC(display, win, 0, NULL);
  XMapWindow(display, win);
  XFlush(display);
  usleep(20000);  // sleep for 20 milliseconds.
  
  // Go into infinite loop
  srand(time(NULL));
  direction = (rand()/(double)(RAND_MAX))*2*PI;

  while(1) {
    XSetForeground(display, gc, 0xFFFFFF);
    XFillRectangle(display, win, gc, 0, 0, WIN_SIZE, WIN_SIZE);

    XSetForeground(display, gc, 0x000000); // black
    XFillArc(display, win, gc, x-RADIUS, y-RADIUS, 2*RADIUS, 2*RADIUS, 0, 360*64);

    // Move the ball forward
    x = x + (int)(SPEED*cos(direction));
    y = y + (int)(SPEED*sin(direction));

    // Check if the ball collides with borders and adjust accordingly
    if (x >= (WIN_SIZE-RADIUS)) {
      direction = PI - direction;
      x = WIN_SIZE-RADIUS;
    }
    else if (x <= RADIUS) {
      direction = PI - direction;
      x = RADIUS;
    }
    if (y >= (WIN_SIZE-RADIUS)) {
      y = WIN_SIZE-RADIUS;
      direction *= -1;
    }
    else if (y <= RADIUS) {
      y = RADIUS;
      direction *= -1;
    }
    XFlush(display);
    usleep(5000);
  }
  
  // Clean up and close the window
  XFreeGC(display, gc);
  XUnmapWindow(display, win);
  XDestroyWindow(display, win);
  XCloseDisplay(display);
}