How can I display a sub-section of a loaded image?

I want to display different segments of a screen-size image, depending upon where a player touches the screen. Sort of a flashlight effect, where your finger is the light source. The image I want to visualize in segments is generally alpha = 0. I use transition.to to view it, which works great - but I really want to view only a piece at a time.

Cutting the image into pieces ahead of time is not feasible, because the number of different possible pieces is very large.

Ideally, I would be able to create a mask 2x screen size, with a hole in it, center the hole at the event x and y, and call transition.to on the whole image - but only the piece visible through the mask would actually fade in.

Anyone have any bright ideas? [import]uid: 65996 topic_id: 11274 reply_id: 311274[/import]

Nobody? Really? [import]uid: 65996 topic_id: 11274 reply_id: 41255[/import]