collision detection with circles

here's a little info on collision detection
http://bretlanius.com/bitmap_2.jpg

You can go to Sampe movie and drag the balls to see example

you can get the movie source for that example at
source

Basically what I've done is to calculate the distance from ball 1 and ball 2 and if it is less than or equal to 24 then they have collided.

PHP Code:

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a=abs (element ("ball1").x - element ("ball2").x);
b=element ("ball1").y - element ("ball2").y;

dist= sqrt (a*a+b*b); 


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Playing around further I came up with the following functions:

PHP Code:

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function distance(element1,element2){
    a=abs (element1.x - element2.x);
    b=element1.y - element2.y;
    return sqrt (a*a+b*b);
}

function collide(distance,width){
    return distance<=width
    } 


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put those in your starting script then when you want to check for a hit do this

PHP Code:

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dist=root.distance(element ("ball1"),element ("ball2"));
hit=root.collide(dist,24); 


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Or better yet let the function do all the work:

PHP Code:

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function C_collide(element1,element2)
    {
    //get width of both elements
    width1=(element1.getBounds().xMax-element1.getBounds().xMin)-5
    width2=(element2.getBounds().xMax-element2.getBounds().xMin)-5
    //get distance 
    a=element1.x - element2.x;
    b=element1.y - element2.y;
    dist= sqrt (a*a+b*b);
    //account for different sizes
    width=(width1/2)+(width2/2);
    //check distance and size
    
    //return t/f
    return dist<=width
    } 


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not sure why I had to subtract 5 from the widths but I found I did.

then call this function like this:

PHP Code:

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hit=root.C_collide(element ("ball1"),element ("ball2")); 


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Hope you find this useful!