[Mesa-dev] [Bug 103852] Rendering errors when running dolphin-emu with Vulkan backend, radv (Super Smash Bros. Melee)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103852

--- Comment #9 from Timothy Arceri <t_arceri at yahoo.com.au> ---
(In reply to Ben Clapp from comment #8)
> Today I spent a number of hours looking at the background rendering errors
> in RenderDoc.
> 
> The vertex shader outputs some vertices that have two vertex colors,
> colors_0 and colors_1. (Only colors_0 is relevant here)
> 
> The fragment shader does a bunch of fiddling around with colors_0, a lot of
> unnecessary conversions and re-assignments that effectively do nothing, and
> ultimately the colors_0 value is passed to rastemp and tevin_d.
> Some more fiddling around and, in the case of the areas of the screen where
> there are rendering errors, the value of colors_0/rastemp/tevin_d ("tevin"
> means "TEV input", referring to the Gamecube/Wii's Texture EnVironment
> hardware) becomes the color value written to the framebuffer.
> 
> The problem is not in the vertex shader, nor is it in the fragment shader.
> For some reason, the value of colors_0 coming out of the vertex shader is
> correct, but the value of colors_0 in the fragment shader is inverted! So
> blue will appear yellow, black while appear white, etc...
> 
> This seems to be a driver bug after all, and so I did try to spend some time
> looking into radv's code to try and see if I could figure out a fix.
> The issue might lie in radv_pipeline.c, I would think it probably has
> something to do with the inter-stage varying colors_0 not getting filled or
> interpreted correctly.
> 
> I've done lots of OpenGL and Vulkan programming, but I have little
> experience with the driver side of things, so while it might be interesting
> to talk a bit with the radv devs and learn a thing or two, I'm not sure how
> much further I can go in terms of looking into this on my own without
> assistance.
> 

Do you think you could get a dump of the NIR and LLVM IR for the shaders in
question and attach it here? You can use the following environment var to dump
the shaders: RADV_DEBUG=shaders

You also might be able to catch the attention of some devs if you jump on the
freenode #radeon IRC channel.

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