Advice on how to accomplish an effect on a tk2d sprite

[iamagiantnerd]

I have a bunch of monster sprites in my game.  I'd like to be able to apply an "ice block" effect.  I mocked something up in gimp to show what I'd like to do:

Before effect applied:


After effect applied:


I could imagine doing this by creating an image dynamically by reading the pixels of the original and manipulating them, but I would think there might be a better way.  Shaders?  I'd appreciate any ideas you folks might have.

Thanks!

[unikronsoftware]

Not the easiest thing to do with shaders. You will need additional information in the alpha channel to be able to perform the outline - one tip is to use 2 thresholds in the alpha, say 0.5 for the outline and 1 for full transparent. When drawing the normal sprite without the outline, it simply uses 0.5 as full transparent.