Is it possible to add an eraser/rubber to paint/drawing app?

Hi,

My kids are playing Dungeons and Dragons. I’d like to create a simple app that allows them to load a map image and then slowly uncover it as the players explore the map (removing the ‘fog’).

My thoughts on this are to create a canvas with the map as the background. Then cover with black paint then allow user to drag over the canvas and erase the black paint.

I’ve tried painting black using the blocks when canvas is created and then setting paint colour to transparent, but it doesn’t paint at all. When I set paint colour to slightly transparent, it seems to ignore it so I assume it’s just not bothering with the alpha channel.

Any ideas for how to slowly ‘eat’ into the black paint would be much appreciated. Could I stamp with a transparent sprite? I can’t find any documentation on how to use Stamp action, so haven’t been able to give this a try.

Many thanks,
Phil.