For Loop collision

**lj81** · 04-24-2012, 11:16 PM

Hi I'm currently writing a program which applies collision detection to balls on the screen. My code works to a certain extent (the balls collide however they do not rebound away from each other) but it is not written efficiently.

Here is the code that partially works:

Java Code:

private void checkForCollision(Ball b[]) {

    double ballX = b[0].getX();
    double ballY = b[0].getY();
    double radiusb = Ball.getRadius();
    double ball4X = b[4].getX();
    double ball4Y = b[4].getY();
    double radiusb4 = Ball.getRadius();
    double ball5X = b[5].getX();
    double ball5Y = b[5].getY();
    double radiusb5 = Ball.getRadius();
    double ball6X = b[6].getX();
    double ball6Y = b[6].getY();
    double radiusb6 = Ball.getRadius();

    double a = ball5X - ballX;
    double bb = ball5Y  - ballY;
    double cc = ball4X - ballX;
    double d = ball4Y - ballY;
    double e = ball5X - ball4X;
    double f = ball5Y - ball4Y;
    double gg = ball6X - ballX;
    double h = ball6Y - ballY;
    double i = ball6X - ball4X;
    double j = ball6Y - ball4Y;
    double k = ball6X - ball5X;
    double l = ball6Y - ball5Y;

    double collide = radiusb4 + radiusb;
    double collide1 = radiusb5 + radiusb;
    double collide2 = radiusb5 + radiusb4;
    double collide3 = radiusb6 + radiusb;
    double collide4 = radiusb6 + radiusb4;
    double collide5 = radiusb6 + radiusb5;

    double c = Math.sqrt((double) (a * a) + (double) (bb * bb));
    double c1 = Math.sqrt((double) (cc * cc) + (double) (d * d));
    double c2 = Math.sqrt((double) (e * e) + (double) (f * f));
    double c3 = Math.sqrt((double) (gg * gg) + (double) (h * h));
    double c4 = Math.sqrt((double) (i * i) + (double) (j * j));
    double c5 = Math.sqrt((double) (k * k) + (double) (l * l));

        if (c < collide){

            performAction(b[0], b[5]);
        }
        else if(c1 < collide1) {

            performAction(b[0],b[4]);

        }
        else if(c2 < collide2) {

            performAction(b[4], b[5]);
        }
        else if(c3 < collide3) {

            performAction(b[6], b[0]);
        }
        else if(c4 < collide4) {

            performAction(b[4], b[6]);
        }
        else if(c5 < collide5) {

            performAction(b[6], b[5]);
        }
    }

I know that this method should be written using a for loop to loop through each ball in turn and get the x and y values. The Ball.getRadius is a static method and and a comparison made with each other ball in subsequent slots of the array. I believe that this should be done using an outer and inner loop which eliminates the need to each ball with every other ball twice. I have made an attempt at it but I'm way off the mark I think so any help you could give me as to how it should be written would be greatly appreciated.

Thanks in advance

Here is my attempt:

Java Code:

for(int i = 0; i < b.length; i ++) {

            b[i] = new Ball(b[i].getX(), b[i].getY(), b[i].getDeltaX(), b[i].getDeltaY());
            Ball.getRadius();

            for(int j = 0; j < b.length; j ++) {

                if(j != i) {

                    double yPosDifference = b[j].getDeltaY() - b[i].getDeltaY();
                    double xPosDifference = b[j].getDeltaX() - b[i].getDeltaX();
                    double collide = b[j].getRadius() + b[i].getRadius();
                    double centres = Math.sqrt((yPosDifference * yPosDifference) + (xPosDifference * xPosDifference));

                    if (centres < collide){

                        performAction(b[i], b[i]);
                    }
                }               
            }
        }
    }