There is such a thing in OpenGL called Bitmaps which are 1-bit images, which could perhaps be used in a similar way to masks, and surely they would be drawn pretty quick, maybe they can be all drawn onscreen first or maybe to the depth buffer or the stencil buffer or something, and use some kind of other feature to do something particular if the values are higher or lower or something, and binary divide it, to get image collision? Then after that draw the real color images?