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  Pong Physics  (Read 3201 times)
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Offline Del-ONE

Senior Newbie

« Posted 2009-02-01 07:56:23 »

Hi, I'm looking for verification on the math I'm using for simple Pong-like physics for arbitrary convex polygons (i.e. collisions always involve a static structure).  So here's my solution:

1. Two bodies collide one of which has a velocity vector and create an intersection
2. The normal to the surface is found by finding the angle from the intersection center to the center of the moving object
3. The velocity vector is reversed by rotating 180 degrees
4. The new velocity vector is flipped over normal angle by adding the angle between the velocity vector and the normal to the normal.

Like this:

Here's my code:
      Rectangle me  = shape.getBounds();
      Rectangle him = ob.getShape().getBounds();
      Rectangle col = me.intersection(him);
      Point meCent = new Point((int)(me.getX()+me.getWidth()/2),(int)(me.getY()+me.getHeight()/2));
      Point colCent = new Point((int)(col.getX()+col.getWidth()/2),(int)(col.getY()+col.getHeight()/2));
      double normAngle = Math.atan2(meCent.getY()-colCent.getY(),meCent.getX()-colCent.getX());
      double velAngle = Math.atan2(dy,dx);
      double newAngle = normAngle+(normAngle-(velAngle-Math.PI));
      //I know this is not the best way to push out of the collision
      move(-5*Math.cos(velAngle), -5*Math.sin(velAngle));

      dx = 50*Math.cos(newAngle);
      dy = 50*Math.sin(newAngle);

I am fairly sure this is conceptually correct, but it never hurts to be sure, besides I got a few questions about it:
-Is this the most efficient way of doing things? (Specifically getting intersection and angles)
-Am I guaranteed that the normal angle will be correct (Assuming I never sink into a collision past the mid-point)
-Am I right in thinking that adding in force, friction, and collisions between 2 moving bodies would not be far off from this?
-Is there a way to easily/effeciently get perfect intersections rather than rectangular approximations

Thanks for the time
Offline Karmington

Senior Devvie

Medals: 1
Projects: 1

Co-op Freak

« Reply #1 - Posted 2009-04-12 01:18:26 »

1. one basics yes all well
2- if you calculate true path accounting speed > paddle width, ok
3 physics more, curves whatever yes indeed
4 rect collision is fastest. if you want more, be it vector or pixel, it will cost you. but these days what is a few
computations here or there?

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