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DrawTransformFeedback() needs to obtain the number of vertices written
to a particular stream during the last Begin/EndTransformFeedback block.
The new driver hook returns exactly that information.
Gallium drivers already implement this by passing the transform feedback
object to the drawing function, counting the number of vertices written
on the GPU, and using draw indirect. This is efficient, but doesn't
always work:
If vertex data comes from user arrays, then the VBO module needs to
know how many vertices to upload, so we need to synchronously count.
Gallium drivers are currently broken in this case.
It also doesn't work if primitive restart is done in software. For
normal drawing, vbo_draw_arrays() performs software primitive restart,
splitting the draw call in two. vbo_draw_transform_feedback() currently
doesn't because it has no idea how many vertices need to be drawn.
The new driver hook gives it that information, allowing us to reuse
the existing vbo_draw_arrays() code to do everything right.
On Intel hardware (at least Ivybridge), using the draw indirect approach
is difficult since the hardware counts primitives, rather than vertices,
which requires doing some simple math. So we always use this hook.
Gallium drivers will likely want to use this hook in some cases, but
want to use the existing draw indirect approach where possible. Hence,
I've added a flag to allow drivers to opt-in to this call.
v2: Make it possible to implement this hook but only use this path
when necessary (suggested by Marek).
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.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. 1) install python 2.7 2) install scons (latest) 3) install mingw, flex, and bison 4) install libxml2 from here: http://www.lfd.uci.edu/~gohlke/pythonlibs get libxml2-python-2.9.1.win-amd64-py2.7.exe 5) install pywin32 from here: http://www.lfd.uci.edu/~gohlke/pythonlibs get pywin32-218.4.win-amd64-py2.7.exe 6) install git 7) download mesa from git see http://www.mesa3d.org/repository.html 8) 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.