[Mesa-dev] [PATCH 0/9] dri2: Swapbuffer update v3.

[Thomas Hellstrom]

Implement back-to-fake-front flips,
Fix EGL_BUFFER_PRESERVED path.
Implement dri3 support for GLX_SWAP_EXCHANGE_OML and GLX_SWAP_COPY_OML.

The back-to-fake-front flips will save a full buffer copy in the case of a
fake front being enabled and GLX_SWAP_UNDEFINED_OML.

Support for EGL_BUFFER_PRESERVED and GLX_SWAP_X_OML are mostly useful for
things like glretrace if traces are capured with applications relying on a
specific swapbuffer behavior.

The EGL_BUFFER_PRESERVED path previously made sure the present was done as
a copy, but there was nothing making sure that after the present,
the same back buffer was chosen.
This has now been changed so that if the previous back buffer is
idle, we reuse it. Otherwise we grab a new and copy the contents and
buffer age from the previous back buffer. Server side flips are allowed.

GLX_SWAP_COPY_OML will behave like EGL_BUFFER_PRESERVED.

GLX_SWAP_EXCHANGE_OML will behave similarly, except that we try to reuse the
previous fake front as the new back buffer if it's idle. If not, we grab
a new back buffer and copy the contents and buffer age from the old fake front.

v2:
- Split the original patch,
- Make sure we have a context for blitImage even if we don't have a
current context.
- Make sure the delayed backbuffer allocation is performed before
glXSwapBuffers, glXCopyBuffers and querying buffer age.
v3:
- squash three patches related to the same change.
- Address review comments by Michel Dänzer.

Testing done:
piglit tests/quick without regressions on svga.
A modified piglit glx-swap-exchange posted for review on the piglit list.
That test required modifying the dri2 state tracke to advertise unconditional
support for GLX_SWAP_EXCHANGE_OML
A piglit glx-swap-copy test derived from the glx-swap-exchange test.
Not posted yet.