Clicking through transparent parts of a bitmap

This message was edited 5 times. Last update was at 19/01/2011 00:27:02

Hello,

I've been working on a project (close to the deadline, meh) that has a 3D view of bitmaps all placed at a random x and z position in space.
These bitmaps are images of people, all .PNG and projected on flat planes facing the camera. The view is interactive, so when the user clicks on a person, the camera zooms in at that particular object.
My problem is that when I click on a transparent part of a bitmap, I can't select underlaying objects. Like clicking next to the head, through legs etc. all 'open' areas.
I tried all well known Flash 3D engines, but without any luck. Is there a way I can simply achieve this with Alternativa?
I guess it has something to do with getObjectsUnderPoint(), pixel comparison, but I don't know how to implement this properly. I already found a similar post here, but that was about Faces, not Sprites.

Any help or example code is much appreciated!