collision

[sudde gameeef]

i was test collision between ball and box. i have a ball and long rect(platform) on screen. the collision part works fine. but i want to test where the ball is touch the platform. so if ball touch the ball from left or right or top or bottom. but when i run this. but it is not seem to be going in any of the inner if statments.

x = ball x
y = ball y
radius = ball width and height
rx = rect x
ry = rect y
rheight = rect height
rwidth = rect width

main game loop:

x += dx;   //keep the ball moving so i can test the collision
y += dy;

 //collsion between ball and box
 if(x+radius > rx && x < rx+rwidth)
 {
    if(y+radius > ry && y < ry+rheight)
	{
	  if(y+radius == ry) 
	    {  
		System.out.println("top");
	    }
	   else  if(y == ry+rheight) 
	    {
		 System.out.println("bottom");
	    }
	   else if(x+radius == rx)
            {
		System.out.println("left");
            }
         else if(x == rx+rwidth)
	    {
		 System.out.println("right");
	    }
   }
}

[Jeff Verdegan]

Add print statements to see the values of your variables and intermediate operations. That way you can see exactly what's happening and learn which of your assumptions are wrong.

System.out.println("x="+ x);
System.out.println("radius=" + radius);
System.out.println("x + radius=" + (x + radius));
System.out.println("rx=" + rx);
System.out.println("x + radius > rx is " + (x + radius > rx));
System.out.println("rwidth=" + rwidth);
System.out.println("rx + rwidth=" + (rx + rwidth));
System.out.println("x < rx + rwdidth is " + (x < rx+rwidth));
System.out.println("x+radius > rx && x < rx+rwidth is" + (x+radius > rx && x < rx+rwidth));

if(x+radius > rx && x < rx+rwidth) {  

    System.out.println("y=" + y);
    // and so on...

    if(y+radius > ry && y < ry+rheight) {  

[sudde gameeef]

yeah.... that isnt working. so i want to try some thing else.


1st check for collision

if(this.getBounds_ball().intersects(this.getBounds_rect())) 

now in side that if statment i can get the over laping x and y. so i know where did the ball collision

xOverlap = getBounds_ball().getX() - getBounds_rect().getX();
yOverlap = getBounds_ball().getY() - getBounds_rect().getY();

now any idea how can i use this information to test where did the ball collide from??

[Campbell Ritchie]

I think this discussion would fit better in the GUIs forum, so I shall move it.
I think you will have to work out how two shapes collide by comparing their locations. Draw two shapes on a piece of paper.

Example: Two “ball”s will collide with a straight line connecting their two centres. That line will consist of radii of the two shapes, and its length and direction can be calculated by the usual geometrical methods, maybe implemented by the hypot and atan2 methods of the Math class.