[Bug 108726] [DXVK] The Witness - transparent objects are not drawn correctly

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108726

Danylo <danylo.piliaiev at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |NOTOURBUG
                 CC|                            |danylo.piliaiev at gmail.com
             Status|NEEDINFO                    |RESOLVED

--- Comment #11 from Danylo <danylo.piliaiev at gmail.com> ---
The culprit is incorrect usage of dual source blending.

commit 00fc56a68d21d7aa91b95f0eaacba59a96c466f5 (HEAD -> master)
Author: Danylo Piliaiev <danylo.piliaiev at gmail.com>
Date:   Fri Jul 20 12:54:42 2018 +0300

    anv: Disable dual source blending when shader doesn't support it on gen8+

    Dual source blending behaviour is undefined when shader doesn't
    have second color output.

     "If SRC1 is included in a src/dst blend factor and
      a DualSource RT Write message is not used, results
      are UNDEFINED. (This reflects the same restriction in DX APIs,
      where undefined results are produced if “o1” is not written
      by a PS – there are no default values defined)."

    Dismissing fragment in such situation leads to a hang on gen8+
    if depth test in enabled.

    Since blending cannot be gracefully fixed in such case and the result
    is undefined - blending is simply disabled.

    v2 (Jason Ekstrand):
     - Apply the workaround to each individual entry
     - Emit a warning through debug_report

    Signed-off-by: Danylo Piliaiev <danylo.piliaiev at globallogic.com>
    Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
    Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

After this commit blending is disabled when rendering with incorrect dual
source blending setup. I can see the error in logs and relevant draw call in
RenderDoc. (Also the same commit exists for OpenGL)

The verdict - not a mesa's bug, most likely it's a game's bug.


When I made that commit I though I was fixing some esoteric issue and now it's
a second game in a month which exhibits it.

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