Nanley Chery
56458cb168
The procedure for decompressing an opaque BC1 Vulkan format is dependant on the
comparison of two colors stored in the first 32 bits of the compressed block.
Here's the specified OpenGL (and Vulkan) behavior for reference:
The RGB color for a texel at location (x,y) in the block is given by:
RGB0, if color0 > color1 and code(x,y) == 0
RGB1, if color0 > color1 and code(x,y) == 1
(2*RGB0+RGB1)/3, if color0 > color1 and code(x,y) == 2
(RGB0+2*RGB1)/3, if color0 > color1 and code(x,y) == 3
RGB0, if color0 <= color1 and code(x,y) == 0
RGB1, if color0 <= color1 and code(x,y) == 1
(RGB0+RGB1)/2, if color0 <= color1 and code(x,y) == 2
BLACK, if color0 <= color1 and code(x,y) == 3
The sampling operation performed on an opaque DXT1 Intel format essentially
hard-codes the comparison result of the two colors as color0 > color1. This
means that the behavior is incompatible with OpenGL and Vulkan. This is stated
in the SKL PRM, Vol 5: Memory Views:
Opaque Textures (DXT1_RGB)
Texture format DXT1_RGB is identical to DXT1, with the exception that the
One-bit Alpha encoding is removed. Color 0 and Color 1 are not compared, and
the resulting texel color is derived strictly from the Opaque Color Encoding.
The alpha channel defaults to 1.0.
Programming Note
Context: Opaque Textures (DXT1_RGB)
The behavior of this format is not compliant with the OGL spec.
The opaque and non-opaque BC1 Vulkan formats are specified to be decoded in
exactly the same way except the BLACK value must have a transparent alpha
channel in the latter. Use the four-channel BC1 Intel formats with the alpha
set to 1 to provide the behavior required by the spec.
v2 (Kenneth Graunke):
- Provide a more detailed commit message.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100925
Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
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 https://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.