Avoid needing to gamma correct for OpenXR

[Manishearth]

Currently when we ask openxr for a color format, it asks for BGRA+sRGB as the highest preference, and then just BGRA (DXGI_FORMAT_B8G8R8A8_UNORM) next. We select that, since that's the format our textures are in. Apparently this leads to OpenXR running gamma-correction.

Ideally we should be able to directly draw to the textures as BGRA+sRGB so that openXR doesn't have any additional work.

[Manishearth]

cc @asajeffrey do you know where in the code we can get the surface to use sRGB?

[jdm]

The answer may be https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_gl_colorspace.txt, but the last time I tried modifying various places in surfman that create surfaces to include it, I just kept getting EGL errors.

[jdm]

Possibly the real answer is the EGL_GL_COLORSPACE parameter of https://www.khronos.org/registry/EGL/sdk/docs/man/html/eglCreatePbufferSurface.xhtml. That being said, for openxr in immersive mode we use eglCreatePbufferFromClientBuffer which doesn't have any mention of SRGB (https://www.khronos.org/registry/EGL/sdk/docs/man/html/eglCreatePbufferFromClientBuffer.xhtml), and that makes me suspect that we might not actually have any other changes?

[jdm]

In particular, see https://chromium.googlesource.com/angle/angle/+/master/extensions/EGL_ANGLE_d3d_texture_client_buffer.txt#161.

[Manishearth]

So if we just create it with sRGB on the openxr side we should be fine? I've been considering this and have a build right now for testing it, but I suspect it's not enough given what they said in Teams.

[jdm]

I think all of us are just guessing at this point :/

[asajeffrey]

From talking with jgilbert, it seems that getting the xr render layer to be sRGB would require some spec work to allow the layer format to be specified.