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Normally, using a non-linear tiling format helps improve cache locality by
ensuring that neighboring pixels are usually close-by in memory. For RGB
formats, this still sort-of holds, but it can also lead to rather terrible
memory access patterns where a single RGB pixel value crosses a tile
boundary and gets split into two pieces in different 4K pages. It also
makes for some rather awkward calculations because your tile size is no
longer an even multiple of surface element size. For these reasons, we
chose to simply never create tiled RGB images in the Vulkan driver.
The GL driver, however, is not so kind so we need to support it somehow. I
briefly toyed with a couple of different schemes but this is the best one I
could come up with. The fundamental problem is that a tile no longer
contains an integer number of surface elements. I briefly considered a
couple other options but found them wanting:
1) Using floats for the logical tile size. This leads to potential
rounding error problems.
2) When presented with a RGB format, just make the tile 3-times as wide.
This isn't so nice because now our tiles are no longer power-of-two
size. Also, it can force the row_pitch to be larger than needed which,
while not strictly a problem for ISL, causes incompatibility problems
with the way the GL driver chooses surface pitches.
The chosen method requires that you pay attention and not just assume that
your tile_info is in the units you think it is. However, it's nice because
it provides a nice "these are the units" declaration in isl_tile_info
itself. Previously, the tile_info wasn't usable as a stand-alone structure
because you had to also know the format. It also forces figuring out how
to deal with inconsistencies between tiling and format back to the caller
which is good because the two different consumers of isl_tile_info really
want to deal with it differently: Computation of the surface size wants
the fewest number of horizontal tiles possible while get_intratile_offset
is far more concerned with things aligning nicely.
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Chad Versace <chadversary@chromium.org>
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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.