SRGB8_ALPHA8 blocks the main thread

Describe the bug

The introduction of SRGB8_ALPHA8 in #22551 improved the render quality of sRGB textures, but also added significant synchronous conversion times that block the main thread. Every sRGB texture adds to the total blocking time, resulting in a poor user experience, especially when the scene contains many textures.

To Reproduce

Steps to reproduce the behavior:

1. Set encoding of any Uint8 RGBA texture to sRGBEncoding. (WebGL 2 context is required.)
2. Render a scene that uses the texture.
3. See the main thread being blocked for a noticeable period of time during the first frame.

Code

The following example loads a cube map and sets its encoding to sRGBEncoding: https://codesandbox.io/s/srgb8-alpha8-wv3jf?runonclick=1&file=/index.js

Live example

• LinearEncoding (0.16 seconds blocking) (Refresh to see small freeze)
• sRGBEncoding (1.49 seconds blocking) (Refresh to see long freeze)

The blocking behaviour can also be observed in live examples that load GLTF models, such as https://threejs.org/examples/?q=gltf#webgl_loader_gltf.

Expected behavior

Ideally, the main thread should not be blocked at all. Blocking time should at least be reduced as much as possible.

Screenshots

With LinearEncoding or sRGBEncoding pre r133	With sRGBEncoding since r133
Longest blocking time = 160 ms	Longest blocking time = 1496 ms

Platform:

• Device: Desktop
• OS: Windows
• Browser: Chrome, Brave, Firefox
• Three.js version: r133

[toji]

As I’ve mentioned on https://bugs.chromium.org/p/chromium/issues/detail?id=1256340 this appears to be an issue with how ANGLE generates mipmaps for sRGB textures.

An effective workaround for this bug (while an ANGLE fix is pending) would be to either:

A) Not use gl.generateMipmaps() with sRGB textures or B) Use texStorage2D when creating the textures.

For those with an affected system, you can see the issue with this (non-Three.js) test page: https://toji.github.io/web-texture-tool/demo/srgb-test.html

Generally I see that it runs fine with the exception of when I select sRGB textures, have it generate mipmaps, and turn off useTexStorage, at which point it janks like crazy.

[kenrussell]

Yes, please file on https://crbug.com/ . The problem might be on the Chromium or ANGLE side, so filing under Chromium is more general. Please include about:gpu in your report, and the zip archive you posted above, and post the bug ID here once filed - thanks in advance.