[Mesa-dev] [Bug 53946] New: [i965] guardband clipping issue on Sandybridge

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=53946

             Bug #: 53946
           Summary: [i965] guardband clipping issue on Sandybridge
    Classification: Unclassified
           Product: Mesa
           Version: git
          Platform: x86-64 (AMD64)
        OS/Version: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: Mesa core
        AssignedTo: mesa-dev at lists.freedesktop.org
        ReportedBy: nkalkhof at web.de


Created attachment 65969
  --> https://bugs.freedesktop.org/attachment.cgi?id=65969
screenshot

Hi,

it seems that guardband clipping on i965(SNB) causes some polygons with normal
vector (0,-1,0) to be clipped. this can be observed with an OpenGL version of
the old DOOM engine. Ceiling planes are being clipped spontaneously while
moving through the scene (see attached screenshot). I've tracked down the bad
commit (85cd30406ff8414bc6ac6de1064d059a4c564160). When I switch off culling
the problem goes away however this comes with the performance panelty.

configure opts:
./configure --prefix=/usr --build=x86_64-pc-linux-gnu
--host=x86_64-pc-linux-gnu --mandir=/usr/share/man --infodir=/usr/share/info
--datadir=/usr/share --sysconfdir=/etc --localstatedir=/var/lib
--libdir=/usr/lib64 --disable-dependency-tracking --enable-dri --enable-glx
--disable-debug --disable-egl --disable-gbm --disable-gles1 --disable-gles2
--enable-glx-tls --enable-asm --enable-shared-glapi --disable-xa
--with-dri-drivers=i965 --with-gallium-drivers= --with-egl-platforms=
--disable-gallium-egl --disable-d3d1x --disable-gallium-g3dvl
--disable-gallium-llvm --disable-openvg --disable-r600-llvm-compiler
--disable-vdpau --disable-xvmc

Could someone please confirm the issue?

Thx and Regards
Nic

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