mirror of
https://gitlab.freedesktop.org/mesa/mesa.git
synced 2026-05-04 22:49:13 +02:00
read-only mirror of https://gitlab.freedesktop.org/mesa/mesa
f7a355556e
A driver which doesn't have async flip support will queue up flips without any
way to replace them afterwards. This means we've got a scanout buffer pinned
as soon as we schedule a flip and so we need another buffer to keep from
stalling.
When vblank_mode=0, if there are only three buffers we do:
current scanout buffer = 0 at MSC 0
Render frame 1 to buffer 1
PresentPixmap for buffer 1 at MSC 1
This is sitting down in the kernel waiting for vblank to
become the next scanout buffer
Render frame 2 to buffer 2
PresentPixmap for buffer 2 at MSC 1
This cannot be displayed at MSC 1 because the
kernel doesn't have any way to replace buffer 1 as the pending
scanout buffer. So, best case this will get displayed at MSC 2.
Now we block after this, waiting for one of the three buffers to become idle.
We can't use buffer 0 because it is the scanout buffer. We can't use buffer 1
because it's sitting in the kernel waiting to become the next scanout buffer
and we can't use buffer 2 because that's the most recent frame which will
become the next scanout buffer if the application doesn't manage to generate
another complete frame by MSC 2.
With four buffers, we get:
current scanout buffer = 0 at MSC 0
Render frame 1 to buffer 1
PresentPixmap for buffer 1 at MSC 1
This is sitting down in the kernel waiting for vblank to
become the next scanout buffer
Render frame 2 to buffer 2
PresentPixmap for buffer 2 at MSC 1
This cannot be displayed at MSC 1 because the
kernel doesn't have any way to replace buffer 1 as the pending
scanout buffer. So, best case this will get displayed at MSC
2. The X server will queue this swap until buffer 1 becomes
the scanout buffer.
Render frame 3 to buffer 3
PresentPixmap for buffer 3 at MSC 1
As soon as the X server sees this, it will replace the pending
buffer 2 swap with this swap and release buffer 2 back to the
application
Render frame 4 to buffer 2
PresentPixmap for buffer 2 at MSC 1
Now we're in a steady state, flipping between buffer 2 and 3
waiting for one of them to be queued to the kernel.
...
current scanout buffer = 1 at MSC 1
Now buffer 0 is free and (e.g.) buffer 2 is queued in
the kernel to be the scanout buffer at MSC 2
Render frames, flipping between buffer 0 and 3
When the system can replace a queued buffer, and we update Present to take
advantage of that, we can use three buffers and get:
current scanout buffer = 0 at MSC 0
Render frame 1 to buffer 1
PresentPixmap for buffer 1 at MSC 1
This is sitting waiting for vblank to become the next scanout
buffer
Render frame 2 to buffer 2
PresentPixmap for buffer 2 at MSC 1
Queue this for display at MSC 1
1. There are three possible results:
1) We're still before MSC 1. Buffer 1 is released,
buffer 2 is queued waiting for MSC 1.
2) We're now after MSC 1. Buffer 0 was released at MSC 1.
Buffer 1 is the current scanout buffer.
a) If the user asked for a tearing update, we swap
scanout from buffer 1 to buffer 2 and release buffer
1.
b) If the user asked for non-tearing update, we
queue buffer 2 for the MSC 2.
In all three cases, we have a buffer released (call it 'n'),
ready to receive the next frame.
Render frame 3 to buffer n
PresentPixmap for buffer n
If we're still before MSC 1, then we'll ask to present at MSC
1. Otherwise, we'll ask to present at MSC 2.
Present already does this if the driver offers async flips, however it does
this by waiting for the right vblank event and sending an async flip right at
that point.
I've hacked the intel driver to offer this, but I get tearing at the top of
the screen. I think this is because flips are always done from within the
ring, and so the latency between the vblank event and the async flip happening
can cause tearing at the top of the screen.
That's why I'm keying the need for the extra buffer on the lack of 2D
driver support for async flips.
Signed-off-by: Keith Packard <keithp@keithp.com>
Acked-by: Jason Ekstrand <jason.ekstrand@intel.com>
Tested-by: Dylan Baker <baker.dylan.c@gmail.com>
|
||
|---|---|---|
| bin | ||
| docs | ||
| doxygen | ||
| include | ||
| m4 | ||
| scons | ||
| src | ||
| .dir-locals.el | ||
| .gitattributes | ||
| .gitignore | ||
| Android.common.mk | ||
| Android.mk | ||
| autogen.sh | ||
| CleanSpec.mk | ||
| common.py | ||
| configure.ac | ||
| install-gallium-links.mk | ||
| install-lib-links.mk | ||
| Makefile.am | ||
| SConstruct | ||
| VERSION | ||
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.