Why does Skia think my gpu doesn't support MSAA?

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Jeru Sanders

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Nov 23, 2021, 11:59:48 AM (10 days ago) Nov 23
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I've been having issues with SkSurface::MakeFromBackendRenderTarget returning me NULL when giving more than 1 sample on Intel iGPUs.

I finally got Skia to build with symbols and see that the issue is here:
skiaSamples.png

This table array only contains a single value, and it's 1. But I think this is impossible because the minimum for OpenGL is 4 samples. Querying GL_MAX_SAMPLES myself correctly returns 16.

It seems to work correctly on my NVIDIA GPUs, but on my Surface Pro 6 (i5 8250U iGPU) and my ASUS E403N (Celeron N3350 iGPU), I'm unable to create an MSAA surface with more than one sample.

I'm currently testing on the chrome/m92 branch for other reasons, but the current main branch build return NULL as well.

I also see:
---- glGetError 0x500(Invalid Enum) at
        C:\_tools\_sdks\skia\skia\src\gpu\gl\GrGLUtil.cpp(108) :
                GetString(0x1F02)

Which could be related (GL_VERSION).

I see there's workaround max_msaa_sample_count_4, but how can I set this in my application without hacking it into my custom version of the library?

Greg Daniel

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Nov 23, 2021, 12:07:03 PM (10 days ago) Nov 23
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We currently disable MSAA on all intel device due to poor performance or driver issues. See https://source.chromium.org/chromium/chromium/src/+/main:third_party/skia/src/gpu/gl/GrGLCaps.cpp;l=4230.

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Jeru Sanders

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Nov 23, 2021, 12:16:50 PM (10 days ago) Nov 23
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Ouch, that's pretty brutal, I guess I can super sample since my content is pretty simple. Any advice on how to do that easily? (Without making a 2x bigger SkCanvas, scaling all my content up, then scaling down the resulting texture)
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