Hello,

I am using the Pong example

http://www.processing.org/learning/examples/collision.html

to help me better understand how collisions work in processing and I have been trying to recreate this program so the paddle hit the ball from left>right instead of the original right>left.

I think the problem is probably something to do with my math but I am not sure. Right now I am kind of stuck and I would appreciate any help. Thanks.

<code>

// 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;
 ///int z=200;
 //if(z>0){
 //z--;}
// ball_x=z;
 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 = 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(dist_wall, paddle_y, paddle_width, paddle_height);  
}
</code>