When rendering the shadow map offscreen using framebuffer objects, it's
not necessary to create a color renderbuffer. Currently
FramebufferParams only lets you choose between a renderbuffer and a
texture for both color and depth attachments. This changes that, and now
you can ask for a texture, a renderbuffer, or nothing.
This improves performance. On my computer, with an 8192x8192 shadow map,
this improves overall frame time by 8.0%.
AbigailBuccaneer