Currently drawAtlas with a blend mode will create a subpass that is as large as the final area needed. For example, if two sprites 50x50 drawn one at 0,0 and one at 1000,1000, then we end up with a 1050x1050 roughly subpass texture.

This is much less efficient than it could be. Since the subpass is only used to create blended texture, we could instead collapse this to a 50x100 texture and then position the sprites when compositing back onto the parent pass. We could even collapse cases where the per sprite color blend and sample is identical.