[Bug 13728] [G965] Some objects in Neverwinter Nights Linux version not displayed correctly

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=13728

--- Comment #28 from Kenneth Graunke <kenneth at whitecape.org> ---
Today I spent some time looking at the TIS-100 bug, because it's a lot simpler
to work with and possibly related.  I discovered that it's a shader with a
discard that isn't working in SIMD16 mode.

The discard handling itself doesn't appear to be the problem.  I can disable
all assembly code that even touches the pixel mask, and it still has the issue.

The render target message length appears to be 15, which is near the limit.

Specifically, these WM_IZ features are in play:

- Discard (kill pixels)
- Depth testing
- Stencil testing and stencil writes
- No depth writes
- No computed depth

Changing any of these appears to fix the issue:

- Eliminating discards at the NIR level (removing the WM_IZ bits and WM_STATE
bits for killpix)
- Disabling stencil testing (brw->stencil_enabled = false, disabling the WM_IZ
bits for stencil)
- Disabling depth testing

I'm pretty sure we're staring right at the problem, but I'm not seeing it yet.

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