wasm/webgl2: buggy ClearColor behavior on various platforms

[rparrett]

Description

Clear color is darker than expected, but occasionally flickers with the correct color.

Repro steps

With an M1 Mac, open Chrome (stable) and visit https://wgpu.rs/examples-gl/?example=cube or https://wgpu.rs/examples-gl/?example=mipmap

Alternately, with Win10 in Firefox follow instructions in the linked bevy issue.

Expected vs observed behavior

Expected a light blue background color, but I see a dark blue color that occasionally flickers light blue.

Extra materials

https://user-images.githubusercontent.com/200550/180576975-4b3c732b-9740-4ddd-8f85-41cc0299e237.mp4

See also: https://github.com/bevyengine/bevy/issues/5426

With bevy in the loop, we're also seeing strange Clear color behavior on Windows in Firefox but I'm so far unsuccessful in reproducing this in a wgpu example.

Platform

This seems to occur only in Stable Chrome for me, so I suppose the issue will eventually fix itself?

Here's the results of testing on various browsers that I have access to on this machine.

	Browser	AdapterInfo
Bug	Chrome 103.0.5060.114	AdapterInfo { name: "ANGLE (Apple, Apple M1 Max, OpenGL 4.1)", vendor: 0, device: 0, device_type: IntegratedGpu, backend: Gl }
Bug	Chrome 103.0.5060.134	AdapterInfo { name: "ANGLE (Apple, Apple M1 Max, OpenGL 4.1)", vendor: 0, device: 0, device_type: IntegratedGpu, backend: Gl }
Ok	Chrome Canary 105.0.5195.0	AdapterInfo { name: "ANGLE (Apple, ANGLE Metal Renderer: Apple M1 Max, Version 12.2.1 (Build 21D62))", vendor: 0, device: 0, device_type: IntegratedGpu, backend: Gl }
Ok	Chrome Canary 105.0.5195.2	AdapterInfo { name: "ANGLE (Apple, ANGLE Metal Renderer: Apple M1 Max, Version 12.2.1 (Build 21D62))", vendor: 0, device: 0, device_type: IntegratedGpu, backend: Gl }
Ok	Safari 15.3 (17612.4.9.1.8)	AdapterInfo { name: "Apple GPU", vendor: 0, device: 0, device_type: Other, backend: Gl }
Ok	Firefox 102.0.1	AdapterInfo { name: "Apple M1", vendor: 0, device: 0, device_type: IntegratedGpu, backend: Gl }
Ok	Firefox Nightly 104.0a1	AdapterInfo { name: "Apple M1", vendor: 0, device: 0, device_type: IntegratedGpu, backend: Gl }

[0xfourzerofour]

I also get this issue on my apple m1 when rendering, would be interesting to see what the issue is

[rparrett]

Worked on this a bit a while back with cwfitzgerald in the bevy discord. Reposting the information here for visibility.

Patching this file to unconditionally set the MESA_I915_SRGB_SHADER_CLEAR resolves the issue for me on MacOS.

The issue on Windows that requires the slightly more involved repro in the linked Bevy issue may be a completely separate issue, because the patch above does not seem to help there.