不规则图片或对象的碰撞检测

下面这个类封装了3个公共的静态方法，简单的碰撞检测可以直接使用complexHitTestObject，需要更加复杂的，那就需要看明白下面的代码，并使用3个公共的静态方法

这个类是一个外国人写的，原文地址如下：
http://www.tink.ws/blog/as-30-hittest

package ws.tink.display
{
        
        import flash.display.BitmapData;
        import flash.display.BlendMode;
        import flash.display.DisplayObject;
        import flash.display.Sprite;
        
        import flash.geom.ColorTransform;
        import flash.geom.Matrix;
        import flash.geom.Point;
        import flash.geom.Rectangle;
        
        public class HitTest
        {

                public static function complexHitTestObject( target1:DisplayObject, target2:DisplayObject,  accurracy:Number = 1 ):Boolean
                {
                        return complexIntersectionRectangle( target1, target2, accurracy ).width != 0;
                }
                
                public static function intersectionRectangle( target1:DisplayObject, target2:DisplayObject ):Rectangle
                {
                        // If either of the items don't have a reference to stage, then they are not in a display list
                        // or if a simple hitTestObject is false, they cannot be intersecting.
                        if( !target1.root || !target2.root || !target1.hitTestObject( target2 ) ) return new Rectangle();
                        
                        // Get the bounds of each DisplayObject.
                        var bounds1:Rectangle = target1.getBounds( target1.root );
                        var bounds2:Rectangle = target2.getBounds( target2.root );
                        
                        // Determine test area boundaries.
                        var intersection:Rectangle = new Rectangle();
                        intersection.x   = Math.max( bounds1.x, bounds2.x );
                        intersection.y    = Math.max( bounds1.y, bounds2.y );
                        intersection.width      = Math.min( ( bounds1.x + bounds1.width ) - intersection.x, ( bounds2.x + bounds2.width ) - intersection.x );
                        intersection.height = Math.min( ( bounds1.y + bounds1.height ) - intersection.y, ( bounds2.y + bounds2.height ) - intersection.y );
                
                        return intersection;
                }
                
                public static function complexIntersectionRectangle( target1:DisplayObject, target2:DisplayObject, accurracy:Number = 1 ):Rectangle
                {                     
                        if( accurracy <= 0 ) throw new Error( "ArgumentError: Error #5001: Invalid value for accurracy", 5001 );
                        
                        // If a simple hitTestObject is false, they cannot be intersecting.
                        if( !target1.hitTestObject( target2 ) ) return new Rectangle();
                        
                        var hitRectangle:Rectangle = intersectionRectangle( target1, target2 );
                        // If their boundaries are no interesecting, they cannot be intersecting.
                        if( hitRectangle.width * accurracy <1 || hitRectangle.height * accurracy <1 ) return new Rectangle();
                        
                        var bitmapData:BitmapData = new BitmapData( hitRectangle.width * accurracy, hitRectangle.height * accurracy, false, 0x000000 ); 

                        // Draw the first target.
                        bitmapData.draw( target1, HitTest.getDrawMatrix( target1, hitRectangle, accurracy ), new ColorTransform( 1, 1, 1, 1, 255, -255, -255, 255 ) );
                        // Overlay the second target.
                        bitmapData.draw( target2, HitTest.getDrawMatrix( target2, hitRectangle, accurracy ), new ColorTransform( 1, 1, 1, 1, 255, 255, 255, 255 ), BlendMode.DIFFERENCE );
                        
                        // Find the intersection.
                        var intersection:Rectangle = bitmapData.getColorBoundsRect( 0xFFFFFFFF,0xFF00FFFF );
                        
                        bitmapData.dispose();
                        
                        // Alter width and positions to compensate for accurracy
                        if( accurracy != 1 )
                        {
                                intersection.x /= accurracy;
                                intersection.y /= accurracy;
                                intersection.width /= accurracy;
                                intersection.height /= accurracy;
                        }
                        
                        intersection.x += hitRectangle.x;
                        intersection.y += hitRectangle.y;
                        
                        return intersection;
                }
                
                
                protected static function getDrawMatrix( target:DisplayObject, hitRectangle:Rectangle, accurracy:Number ):Matrix
                {
                        var localToGlobal:Point;
                        var matrix:Matrix;
                        
                        var rootConcatenatedMatrix:Matrix = target.root.transform.concatenatedMatrix;
                        
                        localToGlobal = target.localToGlobal( new Point( ) );
                        matrix = target.transform.concatenatedMatrix;
                        matrix.tx = localToGlobal.x - hitRectangle.x;
                        matrix.ty = localToGlobal.y - hitRectangle.y;
                        
                        matrix.a = matrix.a / rootConcatenatedMatrix.a;
                        matrix.d = matrix.d / rootConcatenatedMatrix.d;
                        if( accurracy != 1 ) matrix.scale( accurracy, accurracy );

                        return matrix;
                }

        }

}