wipe effect in bge

I all

I’m a beginner

I’m looking for a starting point to make a sort of wipe effect in 2D:

Moving a shape on the screen make appear a texture behind. If the cursor move again over the same path it reveals an other texture behind and again and again.

Is someone can give me an example or a starting point on how to proceed ?

I imagine I have to code a 2d filter actuator in glsl, but i can’t figure out how to set up the scene

Thanx a lot