smudge

[SWF(backgroundColor = 0xCCCCCC)]
var canvas:BitmapData = new BitmapData(stage.stageWidth,stage.stageHeight,true, 0xFFFFFFFF);
addChild(new Bitmap(canvas));
 
var loader:Loader = new Loader();
loader.load(new URLRequest("http://actionsnippet.com/wp-content/chair.jpg"));
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, onComplete);
function onComplete(evt:Event):void{
    canvas.draw(loader);
}
 
var brush:Shape = new Shape();
var diameter:Number = 120;
var radius:Number = diameter / 2;
var matrix:Matrix = new Matrix();
 
var brushAlpha:BitmapData = new BitmapData(diameter, diameter, true, 0x00000000);
drawRadial();
brushAlpha.draw(brush);
 
var xp:Number = 0, yp:Number = 0, px:Number = 0, py:Number = 0;
var dx:Number, dy:Number;
 
stage.addEventListener(MouseEvent.MOUSE_MOVE, onLoop);
function onLoop(evt:Event):void {
    xp = mouseX - radius;
    yp = mouseY - radius;
    dx = xp - px;
    dy = yp - py;
    canvas.copyPixels(canvas,
                    new Rectangle(px, py, diameter, diameter),
                    new Point(xp, yp), brushAlpha, new Point(0,0), true);
    px = xp;
    py = yp
}
 
function drawRadial():void{
    matrix.createGradientBox(diameter, diameter, 0, 0, 0);
    with (brush.graphics){
        beginGradientFill(GradientType.RADIAL, [0xFFFFFF, 0xFFFFFF], [1,0], [0, 255], matrix, SpreadMethod.PAD);
        drawCircle(radius, radius, radius);
    }
}