#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <math.h>
#include <unistd.h>
#include <poll.h>

#define WIDTH 500
#define HEIGHT 500
#define NPTS 500
#define PI 3.14159265359879323846

const int R = 30;
const int MAX_X = WIDTH-2*R;
const int MIN_X = 2*R;
const int MAX_Y = HEIGHT-2*R;
const int MIN_Y = 2*2;
const double THETA = PI/4;
const double T = .25;

double X0 = 10;
double Y0 = 400;
double V0 = 20.3;
double F = 5;
double g = -9.8;
double t = 0;
double px = X0;
double py = Y0;
double vy = V0*sin(THETA);
double vx = V0*cos(THETA);

bool end = false;

Display *D;
int S,Loop,Point;
Window W;
GC Gc,GcRev;
XEvent Event;
XPoint PointBuf[1000],OldPointBuf[1000];

int u_sleep(unsigned int usec);
void get_coord(int& x, int &y);

main() {
  int x, y, oldx, oldy;

  D = XOpenDisplay("");
  S = DefaultScreen(D);
  W = XCreateSimpleWindow(D,DefaultRootWindow(D),0,0,WIDTH,HEIGHT,1,
      WhitePixel(D,S),WhitePixel(D,S));
  XStoreName(D,W,"Bouncing Ball");
  XMapRaised(D,W);

  Gc = XCreateGC(D,W,0L,(XGCValues *) 0);
  XSetForeground(D,Gc,BlackPixel(D,S));
  XSetBackground(D,Gc,WhitePixel(D,S));
  XSetLineAttributes(D,Gc,5,LineSolid,CapButt,JoinMiter);

  GcRev = XCreateGC(D,W,0L,(XGCValues *) 0);
  XSetForeground(D,GcRev,WhitePixel(D,S));
  XSetBackground(D,GcRev,BlackPixel(D,S));
  XSetLineAttributes(D,GcRev,5,LineSolid,CapButt,JoinMiter);

  

  while (!end) {

    oldx = x;
    oldy = y;

    vy = vy + g*T;
    px = px + vx;
    py = py + vy;

    
    if (py <= 0 || py >= MAX_Y) {
      if (vy != 0) {
	if (vy < F && vy > -F) {
	  vy = 0;
	} else {
	  vy = vy > 0 ? vy-F : vy+F;
	  vy = -vy;
	}
      }
    }
    if (px <= 0 || px >= MAX_X) {
      if (vx != 0) {
	if (vx < F && vx > -F) {
	  vx = 0;
	} else {
	  vx = vx > 0 ? vx-F : vx+F;
	  vx = -vx;
	}
      }
    }

    if (px > MAX_X) {
      px = MAX_X;
    } else if (px < 0) {
      px = 0;
    }

    if (py > MAX_Y) {
      py = MAX_Y;
    } else if (py < 0) {
      py = 0;
    }

    get_coord(x,y);

    XFillArc(D,W,GcRev,oldx,oldy,R*2,R*2,0,5760*4);    
    XFlush(D);
    XFillArc(D,W,Gc,x,y,R*2,R*2,0,5760*4);    
    XFlush(D);
    u_sleep(1000);


    t+=T;


  }
  
}

void get_coord(int& x, int& y)
{
  x = (int) px;
  y = MAX_Y - (int) py;


}


int u_sleep(unsigned int usec)
{
  static int subtotal = 0;
  int msec;

  struct pollfd foo;

  subtotal += usec;
  if (subtotal < 1000) return (0);
  msec = subtotal/1000;
  return poll(&foo,(unsigned long)0, msec);
}