Atlas Opacity

[nathan-ahn]

Description

Description

I believe Atlas could cover a wider range of use-cases with support for individual opacity. I've done some experimentation, and as far as I can tell, it's not possible even with creative usage of colors and blendMode. (Closest I've gotten was setting colors using rgba(255, 255, 255, ${opacity}) and blendMode="srcOut", but that loses the opacity of the original texture).

If this is possible, I'd be happy to help out with a pull request with guidance.

Thanks as always for all the awesome work on this package!

[wcandillon]

Could the issue be that colors are expected to be premultiplied? e.g: rgba(${255 * opacity}, ${255 * opacity}, ${255 * opacity}, ${opacity}). I'm closing it for now but let me know if that doesn't fix the issue.

[sergeymorkovkin]

@wcandillon Same here.

I've built a prototype and my results are exactly as @nathan-ahn mentioned: blendMode = srcOut used along with any color uses color alpha channel for specifying opacity of an individual sprite, but when sprites overlap, next rendered sprite completely overrides previously rendered one.

I've tried both: managed expo and prebuilt skia: 1.5.0 and 1.8.2 respectively, but results were the same. #2809

I've also tried attaching a shader to atlas, but that didn't work either - shader has been completely ignored. So, I'm assuming, atlas is using it's own shaders that don't let any other shaders to come into play (not sure of that, just an assumption). Or maybe I were attaching it in a wrong way.

So, what would be a better approach to implement call batching for sprites? Maybe, a custom blending mode? Or maybe a custom fragment shader? And, by the way, does Skia have call batching on it's own?

@wcandillon Kindly advice.

[sergeymorkovkin]

@wcandillon William, I'm willing to contribute into this too, if possible. Pre-multiplied colors didn't work, unfortunately.