[0.1.9][0.1.10] visual glitches in GLES3 renderer on Arch using mesa >25.1.7

[Zsar]

Further detail:

• The shown areas are the same regardless of skin, pose, facing.
• Only skins are affected. All clothing items I could find are unaffected.
• These are the first few starting log lines with mesa <=25.1.7:

$ Games/bdcc-linux/BDCC.x86_64 
Godot Engine v3.6.stable.official.de2f0f147 - https://godotengine.org
glx: failed to create dri3 screen
failed to load driver: nouveau
OpenGL ES 3.0 Renderer: Mesa Intel(R) UHD Graphics (CML GT2)
Async. shader compilation: OFF

• These are the first few starting log lines with mesa 25.2.1 - note the additional errors:

$ Games/bdcc-linux/BDCC.x86_64 
Godot Engine v3.6.stable.official.de2f0f147 - https://godotengine.org
pci id for fd 8: 10de:1f95, driver (null)
pci id for fd 9: 10de:1f95, driver (null)
kmsro: driver missing
glx: failed to create dri3 screen
failed to load driver: nvidia-drm
OpenGL ES 3.0 Renderer: Mesa Intel(R) UHD Graphics (CML GT2)
Async. shader compilation: OFF

• mesa 25.2.2 adds another new error:

$ Games/bdcc-linux/BDCC.x86_64 
Godot Engine v3.6.stable.official.de2f0f147 - https://godotengine.org
pci id for fd 8: 10de:1f95, driver (null)
pci id for fd 9: 10de:1f95, driver (null)
pci id for fd 10: 10de:1f95, driver (null)
glx: failed to create dri3 screen
failed to load driver: nvidia-drm
OpenGL ES 3.0 Renderer: Mesa Intel(R) UHD Graphics (CML GT2)
Async. shader compilation: OFF

This might be a library issue. 50:50 either/or:

• The library fixed a bug that BDCC relied on.
• The library introduced a bug that breaks BDCC.

Possibly related: flickering textures in tech demo reported for Arch package

I have not found a related issue on the mesa repository. It might be sensible to report it, if it turns out not to be something that the game does wrong.

[Alexofp]

Thank you for the report. I don't have Arch or Mesa sadly, I wouldn't even know how to reproduce this issue. Your best bet would be to open the game in the Godot editor and start tinkering with the shader in the MaterialForPartWithSkin.tres material, stripping away stuff until you narrow it down. Sorry

[Zsar]

No worries, that already helps a lot.

I figured out what causes the glitch:

1. went back as far as I can with Godot 3.6, to commit 32f7fd7 , so I can have the simplest version of that file to experiment on.
2. deleted several of the math operation, that were not strictly necessary to display the character at all - no effect, git restore .
3. stripped tags from the render_mode one by one - and bingo: removing depth_draw_alpha_prepass fixes the issue.
4. returned to main HEAD
5. removed exactly depth_draw_alpha_prepass and changed nothing else - yupp, that was it.

... I lack the deeper understanding of Godot to judge whether that sounds like a bug or not - what do you think?

A quick test in the Stocks does not really show anything different without this keyword. - Bodywritings, clothes, cum all seem to display as expected.

What should this tag do?

[Alexofp]

I had problems with transparency I think.. things were displayed in the wrong order. I dunno, I will have to test stuff

[Zsar]

I went ahead and opened an issue at Mesa.

As it is not caused by user code, at this point it pretty much must be Mesa at fault, with Godot as a possible second.