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When converting to a format that has fewer bits the previous code was just shifting off the bits. This doesn't provide very accurate results. For example when converting from 8 bits to 5 bits it is equivalent to doing this: x * 32 / 256 This works as if it's taking a value from a range where 256 represents 1.0 and scaling it down to a range where 32 represents 1.0. However this is not correct because it is actually 255 and 31 that represent 1.0. We can do better with a formula like this: (x * 31 + 127) / 255 The +127 is to make it round correctly. The new code has a special case to use uint64_t when the result of the multiplication would overflow an unsigned int. This function is inline and only ever called with constant values so hopefully the if statements will be folded. The main incentive to do this is to make the CPU conversion path pick the same values as the hardware would if it did the conversion. This fixes failures with the ‘texsubimage pbo’ test when using the patches from here: http://lists.freedesktop.org/archives/mesa-dev/2015-January/074312.html v2: Use 64-bit arithmetic when src_bits+dst_bits > 32 Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com> |
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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 osmesa mesagdi to build classic mesa Windows GDI drivers; or 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.