Paper2D: Drawing primitives into a render texture

Is it possible to draw primitives (lines, triangles…) into a texture? I’m currently playing with Paper2D. To achieve a certain effect I need to create a “mask” texture by drawing shapes into it. This texture has to be updated every frame and multiplied into the rest of the rendered scene. The result is comparable to the example below. Basically it modifies the rendered scene’s brightness, sort of like a post processing effect.

I’ve done it in Cocos2D previously and now I’m thinking about porting it over to UE4 for better portability and because of the convenient editors. How would I go about this in UE4 and Paper2D?