#include "library.h"

const int width = 800, height = 600;
const int padw = 10, padh = 100, padspd = 10;
const double dt = 5.0;

const double pi = acos(-1.0);

double deg_to_rad(double d)
{ return d / 180.0 * pi; }

void main()
{ make_window(width, height);
  set_pen_width(5);

  while (true)
  { fill_rectangle(0, 0, width, height, color::white);
    double bx = random_in_range(0, .9*width);
    double by = random_in_range(0, height);
    double angle = random_in_range(0, 360000) / 1000.0;
    const double speed = 1.0;
    double vx = speed * sin(deg_to_rad(angle));
    double vy = speed * cos(deg_to_rad(angle));
    int pady = height / 2;

    draw_point(bx, by);
    while (true)
    { fill_rectangle(width - padw, pady, padw, padh, color::blue);
      bx += dt*vx;
      by += dt*vy;

      const int key = wait_for_key_typed(0.01);
      if (key == -90)
      { fill_rectangle(width - padw, pady, padw, padh, color::white);
        pady -= padspd;
        if (pady < 0)
          pady = 0; }
      if (key == -88)
      { fill_rectangle(width - padw, pady, padw, padh, color::white);
        pady += padspd;
        if (pady > height - padh)
          pady = height - padh; }

      draw_to(bx, by);
      if (bx >= width)
      { if (by >= pady && by <= pady + padh)
          vx = -vx;
        else
          break; }
      else if (bx <= 0)
        vx = -vx;
      if (by <= 0)
        vy = -vy;
      else if (by >= height)
        vy = -vy; }
    wait(4.0); } }