Color picking with AntiAliasing in OpenGL?

Question

I'm having a problem with color picking and antialiasing in OpenGL. When AA is activated results from glReadPixels are obviously wrong on object edges and object intersections. For example:

I render a box #28 (RGBA: 28, 0, 0, 0) near a box #32 (RGBA: 32, 0, 0, 0). With AA, I can get a wrong ReadPixel value (e.g. 30) where the cube and triangle overlap, or value of 14 on boxes edge, due to the AA algorithm.

I have ~4000 thousand objects I need to be able to pick (it's a jigsaw puzzle game). It is vital to be able to select objects by shape.

I've tried to disable AA with glDisable(GL_MULTISAMPLE) but it does not works with certain AA modes (I read it depends on AA implementation - SS, MS, CS ..)

So, how do I pick an underlying object?

1. A way do temporary disable AA?
2. Using a different buffer or even rendering context?
3. Any other suggestion?

Answer 1

Why not use an FBO as your pick buffer?