// Collision (Pong) 
// by REAS <http://reas.com> 

 
// Global variables for the ball 
float ball_x; 
float ball_y; 
float ball_dir = 1; 
float ball_size = 5;  // Radius 
float dy = 0;  // Direction 
 
// Global variables for the paddle 
int paddle_width = 5; 
int paddle_height = 20; 
 
int dist_wall = 15; 
 
void setup() 
{ 
  size(200, 200); 
  rectMode(CENTER_RADIUS); 
  ellipseMode(CENTER_RADIUS); 
  noStroke(); 
  ball_y = height/2; 
  ball_x = 1; 
  framerate(30); 
} 
 
void draw() 
{ 
  background(51); 
  
  ball_x += ball_dir * 2; 
  ball_y += dy; 
  if(ball_x > width+ball_size) { 
    ball_x = -width/2-ball_size; 
    ball_y = random(0, height); 
    dy = 0; 
  } 
  
  // Constrain paddle to screen 
  float paddle_y = constrain(mouseY, paddle_height, height-paddle_height); 
 
  // Test to see if the ball is touching the paddle 
  float py = width-dist_wall-paddle_width-ball_size; 
  if(ball_x == py 
     && ball_y > paddle_y - paddle_height - ball_size 
     && ball_y < paddle_y + paddle_height + ball_size) { 
    ball_dir *= -1; 
    if(mouseY != pmouseY) { 
      dy = (mouseY-pmouseY)/2.0; 
      if(dy >  5) { dy =  5; } 
      if(dy < -5) { dy = -5; } 
    } 
  } 
  
  // If ball hits paddle or back wall, reverse direction 
  if(ball_x < ball_size && ball_dir == -1) { 
    ball_dir *= -1; 
  } 
  
  // If the ball is touching top or bottom edge, reverse direction 
  if(ball_y > height-ball_size) { 
    dy = dy * -1; 
  } 
  if(ball_y < ball_size) { 
    dy = dy * -1; 
  } 
 
  // Draw ball 
  fill(255); 
  ellipse(ball_x, ball_y, ball_size, ball_size); 
  
  // Draw the paddle 
  fill(153); 
  rect(width-dist_wall, paddle_y, paddle_width, paddle_height);  
}