@ivanpopelyshev the rgb image is actually premultiplied by the artist, which I think is okay to assume as long as it's communicated to the artist. Most artists would save out premultiplied without realizing that is what they are doing anyway.
I see at shader per sprite. I was using TilingSprite.js as an example, and it looks like it's doing it the wrong way. I will work on a version that extends sprite today.