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

[Boris Brezillon]

Hello Marek,

On Tue, 2 Jul 2019 20:09:23 +0200
Boris Brezillon <boris.brezillon at collabora.com> wrote:

> 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.

Any advice on how to solve this problem?

Regards,

Boris