[Bug 107088] [GEN8+] Hang when discarding a fragment if dual source blending is enabled but shader doesn't support it

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Mon Jul 2 13:58:53 UTC 2018


https://bugs.freedesktop.org/show_bug.cgi?id=107088

            Bug ID: 107088
           Summary: [GEN8+] Hang when discarding a fragment if dual source
                    blending is enabled but shader doesn't support it
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: danylo.piliaiev at gmail.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

The hang is reproducible under the next conditions

- Have blending enabled and use GL_SRC1_COLOR in blend function
- Have depth test enabled
- Have fragment shader which doesn't have second color output and discards
fragments
- Draw something with this shader
- Hang will occur 

The hang was found in Unigine Heaven 4.0 running in dx11 mode under wine during
the investigation of the bug
https://bugs.freedesktop.org/show_bug.cgi?id=103556. I believe this two hangs
are separate issues since one in the original bug seems to happened with native
Unigine version and doesn't happen anymore.

The situation when dual color blending is enabled but shader doesn't support it
is undefined as stated in documentation (vol.7 3D-Media-GPGPU):

"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). If SRC1 is not included in a src/dst
blend factor, dual source blending must be disabled."

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