[Webkit-unassigned] [Bug 222822] New: WebGL2: SRGB8_ALPHA8 *sometimes* does not linearize texture color

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=222822

            Bug ID: 222822
           Summary: WebGL2: SRGB8_ALPHA8 *sometimes* does not linearize
                    texture color
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Mac (Intel)
                OS: macOS 11
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGL
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: brendanduncan at gmail.com
                CC: dino at apple.com, kbr at google.com, kkinnunen at apple.com

Created attachment 422412

  --> https://bugs.webkit.org/attachment.cgi?id=422412&action=review

An html+video example to test the SRGB8_ALPHA8 format for video textures

I attached a test example to demonstrate the issue. 
The test works on Chrome, and I have yet to have it fail on iOS 14.5 beta 2 Safari, but on macOS Safari Tech Preview 121 (Safari 14.2, WebKit 16612.1.4.3) the test fails about 1/10 times of refreshing the page. This is better than Firefox, which fails every time.

I iterate on the tests by refreshing the page and visually looking at the results.

The example loads a video and has 3 canvases with WebGL2 contexts. It draws the video frame into each of these canvases with different texture formats.
The first video uses the gl.SRGB8 internal format; the second uses the gl.SRGB8_ALPHA8 format; and the third uses the unmodified gl.RGBA format to use as a test basis.

Both of the SRGB8* formats should be linearizing the texture color. But when the test fails, the SRGB8_ALPHA8 version is not linearized, it's staying in the original sRGB color.

The previous version of the Safari Tech Preview, the failure rate was about 50% of the time of refreshing the page, so great progress, but there still seems to be something not quite right, maybe a race condition somewhere or a caching issue...

This (and Firefox not working) is keeping Unity from being able to use SRGB8_ALPHA8 for video textures in linear color space, we have to keep them as SRGB8 only.

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