// Global variables for the ball
  float ball_x;
  float ball_y;
  float ball_dir = 1;
  float ball_size = 15;  // Radius
  float dy = 0;  // Direction
  
  // Global variables for the paddle
  int paddle_width = 10;
  int paddle_height = 60;
  
  int dist_wall = 15;
  
  void setup()
  {
    size(640, 360);
    rectMode(RADIUS);
    ellipseMode(RADIUS);
    noStroke();
    smooth();
    ball_y = height/2;
    ball_x = 1;
  }
  
  void draw() 
  {
    background(51);
    
    ball_x += ball_dir * 1.0;
    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);  
  }