[Mesa-dev] [PATCH v5 4/5] st/dri2: Implement DRI2bufferDamageExtension

[Boris Brezillon]

On Tue, 2 Jul 2019 13:21:31 -0400
Marek Olšák <maraeo at gmail.com> wrote:

> On Tue., Jul. 2, 2019, 09:50 Boris Brezillon,
> <boris.brezillon at collabora.com> wrote:
> 
> > From: Daniel Stone <daniels at collabora.com>
> >
> > Add a pipe_screen->set_damage_region() hook to propagate
> > set-damage-region requests to the driver, it's then up to the
> > driver to decide what to do with this piece of information.
> >
> > If the hook is left unassigned, the buffer-damage extension is
> > considered unsupported.
> >
> > Signed-off-by: Daniel Stone <daniels at collabora.com>
> > Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
> > Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
> > ---
> > Changes in v5:
> > * Add Alyssa's R-b
> > ---
> >  src/gallium/include/pipe/p_screen.h   |  7 +++++++
> >  src/gallium/state_trackers/dri/dri2.c | 22 ++++++++++++++++++++++
> >  2 files changed, 29 insertions(+)
> >
> > diff --git a/src/gallium/include/pipe/p_screen.h
> > b/src/gallium/include/pipe/p_screen.h
> > index 3f9bad470950..8df12ee4f865 100644
> > --- a/src/gallium/include/pipe/p_screen.h
> > +++ b/src/gallium/include/pipe/p_screen.h
> > @@ -464,6 +464,13 @@ struct pipe_screen {
> >     bool (*is_parallel_shader_compilation_finished)(struct
> > pipe_screen *screen,
> >                                                     void *shader,
> >                                                     unsigned
> > shader_type); +
> > +   /**
> > +    * Set damage region.
> >  
> 
> Can you expand the comment to describe rects? The format of rects is
> not obvious.

Oops, will point to the KHR_partial_update() doc and explain what rects
encode and how.
This reminds me that we have a corner case (at least for tile-based
GPUs): the dri implementation calls
->set_damage_region(screen, res, 0, NULL) to reset the damage region,
but in KHR_partial_update() spec this means "damage all". If we follow
the spec that would imply existing FB content is dropped which in turn
means users relying on buffer_age() (without partial_update()) to only
update the region that have changed will stop working properly.

I see 2 options to solve this problem:

1/ add a new ->reset_damage_region() hook that would be called by the
   dri implementation after each swap_buf() in replacement of the
   current ->set_damage_region(screen, res, 0, NULL). Reset in that
   case means we consider the damage region as "unknown" and force
   a "reload FB content in the local-tile buffer" for the whole
   resource instead of restricting it to the !damage region.
2/ deviate from the KHR_partial_update() semantic and reserve
   ->set_damage_region(screen, res, 0, NULL) for the "reset damage
   region" op. That means we'll have to convert actual
   KHR_partial_update(0, NULL) calls into
   ->set_damage_region(screen, res, 1, full_res_rect) ones to reflect
   the behavior described in the spec.