[Mesa-dev] [PATCH 00/10] i965/gen6: Begin implementing MSAA.

[Paul Berry]

This patch series provides preliminary support for MSAA (multisample
antialiasing) in i965/gen6.

The key difficulty in implementing MSAA is that we have to allow the
user to blit between arbitrary combinations of MSAA and non-MSAA
renderbuffers.  In particular, we need to be able to blit from an MSAA
buffer to a non-MSAA buffer, and in doing so, blend all of the
constituent samples from one pixel together into a single color value.
We can't do this using the hardware blitter or the existing blit
meta-op, since neither mechanism supports blending together the
constituent samples.  Also, MSAA surfaces must be Y-tiled, and the
hardware blitter doesn't support Y tiling.

This leaves two possibilities: extend the meta-op to be able to
perform the necessary blending, or do the blit using the GPU's 3D
render path and some custom shader programs written in GPU assembly.
I've chosen the latter alternative, since this will allow the blit to
be faster (especially on Gen7, where it is possible to recognize
pixels that do not need blending and avoid extra texel fetches).  An
additional benefit of this approach is that we will be able to re-use
this "blit using the render path" mechanism to speed up operations
that are currently done on the CPU (such as copying data between a
depth/stencil buffer and a separate stencil buffer).

In order to perform blits using the render path, I've re-purposed the
existing HiZ code into a more general purpose component called
"blorp", which stands for "BLit Or Resolve Pass"*.  Most of the
patches that follow simply reorganize the HiZ code into a form which
allows blitting functionality to be added to it.  The second-to-last
patch in the series actually adds blitting capability, and the last
patch adds MSAA support.

MSAA support is still preliminary; however since the driver *claims*
to support GL 3.0 (and MSAA is a required part of GL 3.0), I think it
is reasonable to turn it on now and address the remaining limitations
as future "bug fix" patches.  Most of the work left to do is
documented in "TODO" comments in the patches to follow (the two
exceptions are centroid interpolation and coverage parameters, which I
haven't yet started on).

*Another possible backronym for "blorp" is "BLit On Render Path", but
sadly this doesn't convey the fact that the code is still used for HiZ
resolves.

[PATCH 01/10] intel: Add extern "C" declarations to headers
[PATCH 02/10] intel: Work around differences between C and C++ scoping rules.
[PATCH 03/10] i965/hiz: Make void pointer type casts explicit
[PATCH 04/10] i965/hiz: Convert gen{6,7}_hiz.c to C++
[PATCH 05/10] i965/hiz: Convert gen{6,7}_hiz.h to gen{6,7}_blorp.h
[PATCH 06/10] i965: Parameterize HiZ code to prepare for adding blitting.
[PATCH 07/10] i965: split gen{6,7}_blorp_exec functions into manageable chunks.
[PATCH 08/10] i965: Expose surface setup internals for use by blits.
[PATCH 09/10] i965/gen6+: Add code to perform blits on the render path ("blorp").
[PATCH 10/10] i965/gen6: Initial implementation of MSAA.