compositor: Fix culling of repaints behind opaque surfaces

Culling of the repaint of a surface behind an opaque surface on the
same plane was broken by commit 547149a9 [1]. The idea of that commit
is that the damage obscured by an overlay would remain on the primary
plane damage and be repainted when the overlay moved. However, in the
case the two surfaces are on the same plane, the opaque one is not
obscured, so it ends up being repainted.

This commit adds an opaque field to struct weston_plane, that is built
incrementally when accumulating damage. The opaque region of surfaces
on the same plane are removed from the plane's damage, restoring the
previous culling behavior. But since damage behind opaque region of
other planes is maintained, the bug solved in the mentioned commit is
not regressed.

https://bugs.freedesktop.org/show_bug.cgi?id=56537

src/compositor-drm.c

@@ -793,10 +793,26 @@ drm_assign_planes(struct weston_output *output)
 {
 	struct drm_compositor *c =
 		(struct drm_compositor *) output->compositor;
+	struct drm_output *drm_output = (struct drm_output *) output;
+	struct drm_sprite *s;
 	struct weston_surface *es, *next;
 	pixman_region32_t overlap, surface_overlap;
 	struct weston_plane *primary, *next_plane;
 
+	/* Reset the opaque region of the planes */
+	pixman_region32_fini(&drm_output->cursor_plane.opaque);
+	pixman_region32_init(&drm_output->cursor_plane.opaque);
+	pixman_region32_fini(&drm_output->fb_plane.opaque);
+	pixman_region32_init(&drm_output->fb_plane.opaque);
+
+	wl_list_for_each (s, &c->sprite_list, link) {
+		if (!drm_sprite_crtc_supported(output, s->possible_crtcs))
+			continue;
+
+		pixman_region32_fini(&s->plane.opaque);
+		pixman_region32_init(&s->plane.opaque);
+	}
+
 	/*
 	 * Find a surface for each sprite in the output using some heuristics:
 	 * 1) size

src/compositor.c

@@ -925,10 +925,15 @@ surface_accumulate_damage(struct weston_surface *surface,
 					  surface->geometry.y - surface->plane->y);
 	}
 
+	pixman_region32_subtract(&surface->damage,
+				 &surface->damage, &surface->plane->opaque);
 	pixman_region32_union(&surface->plane->damage,
 			      &surface->plane->damage, &surface->damage);
 	empty_region(&surface->damage);
 	pixman_region32_copy(&surface->clip, opaque);
+	pixman_region32_union(&surface->plane->opaque,
+			      &surface->plane->opaque,
+			      &surface->transform.opaque);
 	pixman_region32_union(opaque, opaque, &surface->transform.opaque);
 }
 
@@ -968,6 +973,9 @@ weston_output_repaint(struct weston_output *output, uint32_t msecs)
 
 	pixman_region32_init(&opaque);
 
+	pixman_region32_fini(&ec->primary_plane.opaque);
+	pixman_region32_init(&ec->primary_plane.opaque);
+
 	wl_list_for_each(es, &ec->surface_list, link)
 		surface_accumulate_damage(es, &opaque);
 
@@ -1455,6 +1463,7 @@ WL_EXPORT void
 weston_plane_init(struct weston_plane *plane, int32_t x, int32_t y)
 {
 	pixman_region32_init(&plane->damage);
+	pixman_region32_init(&plane->opaque);
 	plane->x = x;
 	plane->y = y;
 }
@@ -1463,6 +1472,7 @@ WL_EXPORT void
 weston_plane_release(struct weston_plane *plane)
 {
 	pixman_region32_fini(&plane->damage);
+	pixman_region32_fini(&plane->opaque);
 }
 
 static  void

src/compositor.h

@@ -270,6 +270,7 @@ struct weston_layer {
 
 struct weston_plane {
 	pixman_region32_t damage;
+	pixman_region32_t opaque;
 	int32_t x, y;
 };