Animated textures

[deathcap]

Change the texture index for a voxel over a specified time interval (animation frame lengths)

reference: http://www.arcsynthesis.org/gltut/Positioning/Tut03%20Multiple%20Shaders.html

note: this shouldn't require re-uploading the texture atlas on each frame (expensive); just have all the frames in the atlas and change the UVs over time