more efficient animations

re-implemented animations by combining all frames of a drawing in a single texture and scrolling texture offset when animation needs to be updated. this is a major performance improvement from the previous implementation when frames were treated as separate meshes. performance boost is clearly noticeable in larger scenes with many animated drawings

if you released a bitsy 3d game before this update, you might want to update it with this newer version to improve performance, especially if there are large scenes with animations