円とアルファ

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

package {
    import flash.display.Sprite;
    import flash.events.Event;
    public class FlashTest extends Sprite {
        public function FlashTest() {
            // write as3 code here.
            var base:Sprite = new Sprite();
            addChild(base);
            base.x = stage.stageWidth / 2;
            base.y = stage.stageHeight / 2;
            
            base.graphics.beginFill(0xFF3399);
            base.graphics.drawCircle(0, 0, 10);
            
            base.addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }
        
        private function onEnterFrame(e:Event):void {
        		var b:Sprite = e.currentTarget as Sprite;
        		var d:Number = Math.sqrt( Math.pow(stage.mouseX - stage.stageWidth / 2, 2) + Math.pow(stage.mouseY - stage.stageHeight / 2, 2));
        		var a:Number = 1 - (d / 100);
        		b.graphics.clear();
        		b.graphics.beginFill(0xFF3399, a);
        		b.graphics.drawCircle(0,0,d);
        		b.graphics.endFill();
        }
    }
}