Use a PGraphic instead.

For the source image, the mask image or both.

Then it can be dynamic in many ways.

Actually, I have made a window with particles inside using some physics library,

Yeah.

Here is an example on OpenProcessing. As you can see it draws to a PGraphics called tile, which is subsequently rotatated etc. For a first step also check out this thread in the old forum. I'm thinking PGraphic is the way to go.

Either indirectly (copy part of the screen to a PGraphic, then rotate etc) or directly (draw to PGraphic, then rotate etc).