Re: [PATCH 1/2] compositor: Clear only the the damage that was actually repainted

[Ander Conselvan de Oliveira]

Em 15-08-2012 23:02, Kristian Høgsberg escreveu:
On Tue, Aug 14, 2012 at 03:26:49PM +0300, Ander Conselvan de Oliveira wrote:
From: Ander Conselvan de Oliveira <ander.conselvan.de.olive...@intel.com>
Instead of clearing the whole output region after a repaint, clear
only the regions that were actually painted. This way, the damage
added when a surface moves from the primary plane to another one is
kept while this region is obscured by the opaque region. This allows
the contents below an overlaid surface to be culled, but to make this
work properly, it is also necessary to change the way previous damage
is drawn.

Consider the following scenario: a surface is moved to an overlay plane
leaving some damage in the primary plane. On the following frame, the
surface on the overlay moves, revealing part of the damaged region on
the primary plane. On the frame after that, the overlaid surface moves
back to its previous position obscuring the region of the primary plane
repainted before. At this point, the repainted region was added to the
output's previous damage so that it is draw to both buffers. But since
this region is now obscured, the redrawing is skipped. If the overlaid
surface moves again revealing this region, one of the buffers actually
contains the wrong content.

To fix this problem, this patch ensures that any previous damage that
would be lost is actually drawn, by subtracting it from the opaque
region.

Ah, hm, ok... that's really subtle.  Good analysis.  Now with your
fix, we still repaint when we move the opaque overlay back over a
region with "old damage" even though it's not visible.  How about
unioning output->previous_damage into the primary plane damage just
before repainting?  That way, if any old damage doesn't get repainted,
we add it back to the primary plane damage.  The only drawback here is
that we move the overlay away again, we could end up repainting that
area again.  But once all buffers has repainted the area, the residual
damage will disappear.

I've tweaked your patch to do that and attached it.  I think it's a
slight improvement, in that we probably typically end up painting less
and it's a little simpler.

Yeah, that looks better. You did, however, remove one too many lines 
from surface_accumulate_damage() so the opaque region is always empty.

However, either approach is a workaround
how we should track the damage per buffer.  When we repaint an output,
we add the new damage (from primary_plane.damage) to all buffers
damage, then render the damage (clipped by opaque regions) in current
back buffers damage region, subtracting what we render.  This also
scales to triple buffering.

And with some refactoring to track this on a per plane basis, it can 
also scale to the case where there are multiple surfaces in an ARGB overlay.


Ander



Kristian

---
  src/compositor.c |   26 ++++++++++++++++++--------
  1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/src/compositor.c b/src/compositor.c
index 7370435..26c57b9 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -928,6 +928,9 @@ weston_surface_draw(struct weston_surface *es, struct 
weston_output *output,
        if (!pixman_region32_not_empty(&repaint))
                goto out;

+       pixman_region32_subtract(&ec->primary_plane.damage,
+                                &ec->primary_plane.damage, &repaint);
+
        glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
        if (es->blend || es->alpha < 1.0)
                glEnable(GL_BLEND);
@@ -1095,7 +1098,8 @@ update_shm_texture(struct weston_surface *surface)

  static void
  surface_accumulate_damage(struct weston_surface *surface,
-                         pixman_region32_t *opaque)
+                         pixman_region32_t *opaque,
+                         pixman_region32_t *exclude)
  {
        if (surface->buffer && wl_buffer_is_shm(surface->buffer))
                update_shm_texture(surface);
@@ -1121,9 +1125,8 @@ surface_accumulate_damage(struct weston_surface *surface,
        pixman_region32_union(&surface->plane->damage,
                              &surface->plane->damage, &surface->damage);
        empty_region(&surface->damage);
-       pixman_region32_copy(&surface->clip, opaque);
-       if (surface->plane == &surface->compositor->primary_plane)
-               pixman_region32_union(opaque, opaque, 
&surface->transform.opaque);
+       pixman_region32_subtract(&surface->clip, opaque, exclude);
+       pixman_region32_union(opaque, opaque, &surface->transform.opaque);
  }

  static void
@@ -1135,7 +1138,7 @@ weston_output_repaint(struct weston_output *output, 
uint32_t msecs)
        struct weston_animation *animation, *next;
        struct weston_frame_callback *cb, *cnext;
        struct wl_list frame_callback_list;
-       pixman_region32_t opaque, output_damage;
+       pixman_region32_t opaque, output_damage, previous;
        int32_t width, height;

        weston_compositor_update_drag_surfaces(ec);
@@ -1170,8 +1173,16 @@ weston_output_repaint(struct weston_output *output, 
uint32_t msecs)

        pixman_region32_init(&opaque);

+       /* Once we draw something on one of the back buffers it needs to be
+        * drawn on the other one, otherwise we might endup with artifacts.
+        * Make sure we draw any previous damage that would be lost otherwise
+        */
+       pixman_region32_init(&previous);
+       pixman_region32_subtract(&previous, &output->previous_damage,
+                                &ec->primary_plane.damage);
+
        wl_list_for_each(es, &ec->surface_list, link)
-               surface_accumulate_damage(es, &opaque);
+               surface_accumulate_damage(es, &opaque, &previous);

        pixman_region32_init(&output_damage);
        pixman_region32_union(&output_damage, &ec->primary_plane.damage,
@@ -1180,10 +1191,9 @@ weston_output_repaint(struct weston_output *output, 
uint32_t msecs)
                             &ec->primary_plane.damage);
        pixman_region32_intersect(&output_damage,
                                  &output_damage, &output->region);
-       pixman_region32_subtract(&ec->primary_plane.damage,
-                                &ec->primary_plane.damage, &output->region);

        pixman_region32_fini(&opaque);
+       pixman_region32_fini(&previous);

        if (output->dirty)
                weston_output_update_matrix(output);
--
1.7.9.5

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