Simple axis-aligned ellipsoid overlap check

by Glidias

Just some simple relative scaling from the sum or radii, and scale displacements to local coordinate space of either one accordingly. For further optimization, sum of radii scaling factors can be precomputed (to avoid division per frame) if these don't change often under a 1-many check.

♥0 | Line 55 | Modified 2013-09-24 22:24:10 | MIT License

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ActionScript3 source code

/**
 * Copyright Glidias ( http://wonderfl.net/user/Glidias )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/eFkY
 */

package {
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.events.Event;
    public class SimpleEllipsoidOverlapCheck extends Sprite {
        
        private var pEclipse:Eclipse;
        private var other:Eclipse;

        public function SimpleEllipsoidOverlapCheck() {
            // write as3 code here..
            addChild(pEclipse = new Eclipse(16, 32, 0xFF0000));
            addChild(other = new Eclipse(46,24 , 0x0000FF));
            other.x = 144;
            other.y = 155;
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
            stage.align = StageAlign.TOP_LEFT;
            stage.scaleMode = StageScaleMode.NO_SCALE;
        }
        
        private function onEnterFrame(e:Event):void 
        {
            var px:Number;
            var py:Number;
            var ox:Number = other.x;
            var oy:Number = other.y;
            
            pEclipse.x = px = mouseX;
            pEclipse.y = py = mouseY;
            var rx:Number = pEclipse.rx + other.rx;
            var ry:Number = pEclipse.ry + other.ry;
            var pRadius:Number = rx > ry ? rx :ry;
            var prScaleX:Number =  pRadius / rx;
            var prScaleY:Number =  pRadius / ry;
            
            // check if overlap
            var dx:Number = ox - px;
            var dy:Number = oy - py; 
            //var dz:Number = pz - oz;
            dx *= prScaleX;
            dy *= prScaleY;

            var d:Number = dx * dx + dy * dy;
            if (d <= pRadius*pRadius) {
                 pEclipse.alpha = .5;
            }
            else pEclipse.alpha = 1;
            
        }
    }
}
import flash.display.Shape;

class Eclipse extends Shape {
    public var rx:Number;
    public var ry:Number;
    public function Eclipse(rx:Number, ry:Number, color:uint):void {
        graphics.beginFill(color, 1);
        graphics.drawCircle(0,0,1);
        scaleX = rx;
        scaleY = ry;
        this.rx = rx;
        this.ry = ry;
        
    }
    
}