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When blending with GL_COLORBURN_KHR and these colors:
dst = <0.372549027, 0.372549027, 0.372549027, 0.372549027>
src = <0.09375, 0.046875, 0.0, 0.375>
the normalized dst value became 0.99999994 (due to precision problems
in the floating point divide of rgb by alpha). This caused the color
burn equation to fail the dst >= 1.0 comparison. The blue channel would
then fall through to the dst < 1.0 && src >= 0 comparison, which was
true, since src.b == 0. This produced a factor of 0.0 instead of 1.0.
This is an inherent numerical instability in the color burn and dodge
equations - depending on the precision of alpha scaling, the value can
be either 0.0 or 1.0. Technically, GLSL floating point division doesn't
even guarantee that 0.372549027 / 0.372549027 = 1.0. So arguably, the
CTS should allow either value. I've filed a bug at Khronos for further
discussion (linked below).
In the meantime, this patch improves the precision of alpha scaling by
replacing the division with (rgb == alpha ? 1.0 : rgb / alpha). We may
not need this long term, but for now, it fixes the following CTS tests:
ES31-CTS.blend_equation_advanced.blend_specific.GL_COLORBURN_KHR
ES31-CTS.blend_equation_advanced.blend_all.GL_COLORBURN_KHR_all_qualifier
Cc: currojerez@riseup.net
Cc: mesa-stable@lists.freedesktop.org
Bugzilla: https://cvs.khronos.org/bugzilla/show_bug.cgi?id=16042
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
(cherry picked from commit
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| configure.ac | ||
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File: docs/README.WIN32 Last updated: 21 June 2013 Quick Start ----- ----- Windows drivers are build with SCons. Makefiles or Visual Studio projects are no longer shipped or supported. Run scons libgl-gdi to build gallium based GDI driver. This will work both with MSVS or Mingw. Windows Drivers ------- ------- At this time, only the gallium GDI driver is known to work. Source code also exists in the tree for other drivers in src/mesa/drivers/windows, but the status of this code is unknown. Recipe ------ Building on windows requires several open-source packages. These are steps that work as of this writing. - install python 2.7 - install scons (latest) - install mingw, flex, and bison - install pywin32 from here: http://www.lfd.uci.edu/~gohlke/pythonlibs get pywin32-218.4.win-amd64-py2.7.exe - install git - download mesa from git see http://www.mesa3d.org/repository.html - run scons General ------- After building, you can copy the above DLL files to a place in your PATH such as $SystemRoot/SYSTEM32. If you don't like putting things in a system directory, place them in the same directory as the executable(s). Be careful about accidentially overwriting files of the same name in the SYSTEM32 directory. The DLL files are built so that the external entry points use the stdcall calling convention. Static LIB files are not built. The LIB files that are built with are the linker import files associated with the DLL files. The si-glu sources are used to build the GLU libs. This was done mainly to get the better tessellator code. If you have a Windows-related build problem or question, please post to the mesa-dev or mesa-users list.