This patch allows the drawing of the mesh selection ids to be done on a texture with 32UI format.
This simplifies the shader that previously acted on the backbuffer and had to do an uint to rgba conversion.
The size of framebuber and glViewport is now limited to the size of the threshold.
TODO:
The threshold keeps changing between selecting one element type for another, for better optimization, maintaining the same threshold would avoid having to re-create the framebuffer textures.