How to set mouse click to do not hit transparent pixels - actionscript-3

Question

Imagine a painting program. I have two imagens overlaping each other. I must be able to click on the image behind if I click on a transparent part of the above one.
I add an event listener on each image. So I must prevent the first one to dispatch click event in order to the behind one dispatch it.
(I mean, I already check for transparent pixels, but i can't cancel that event to the other imagem dispatch it.)

Answer 1

There is some dirty solution. Say your "images" are encapsulated in Sprites, otherwise you can't attach a listener to a Bitmap object or a Shape object. MovieClips - well, should still work, although checking alpha is a lot harder. You have your listeners attached to those sprites. First, that sprite in itself can check transparency, and if not transparent, proceed the event. To get what's behind, you can call stage.getObjectsUnderPoint(), this will return an Array of DisplayObjects, with foreground being on top. So you might have one single listener that would call this to enumerate what's under the point, then do as Roman Trofimov advises to determine that object's transparency. Once you'll find a non-transparent object, you do:
// "b" is a non-transparent DisplayObject found beforehand
while (b && (!(b is InteractiveObject))) b = b.parent;
if (b) {
var p:Point = new Point(e.stageX, e.stageY);
p = b.globalToLocal(p);
b.dispatchEvent(new MouseEvent('click', true, true, p.x, p.y));
}
This will dispatch a click event to the object that's able to receive events, and is opaque enough to obscure the background.

Answer 2

The MovieClip property 'mouseEnabled' can prevent click events from triggering on objects in front of other objects, for example, take two movie clips of the same size and same position:
mc1.addEventListener(MouseEvent.CLICK, click1);
function click1(e:MouseEvent) : void
{
trace("1");
}
mc2.addEventListener(MouseEvent.CLICK, click2);
function click2(e:MouseEvent) : void
{
trace("2");
}
mc1.mouseEnabled = false;
Output would be "2" as the click would essentially go 'through' mc1.

Answer 3

In flex you can add mouseEnabledWhereTransparent="false" to components. Not fully sure if that variable is available to you though

Answer 4

Generally, you will always get first event from first sprite (if it was not capture phase ot priority change). But as I understand, you need to check was it transparent and if not - stop bubbling this event.
To stop event - use event.stopImmediatePropagation() in event handler.
To determine transparency:
1) If it is just only the one bitmap, you can check its .bitmapData with method .getPixel32, it returns you alpha value.
2) If it is combined sprite (vector and bitmap), you need to manually render it to Bitmap using BitmapData.draw and then use solution from second case
3) To understand if it was absolutelly miss click, you can try this method: Check transparency