cc: Make occlusion a draw property.

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index c48a09a23aeef1fc77c547dce2e9afc284ea3257..efe05896d8f7736b8f472290bec0561c96826b1b 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -580,63 +580,71 @@ bool LayerTreeImpl::UpdateDrawProperties() {
     TRACE_EVENT_BEGIN2("cc", "LayerTreeImpl::UpdateTilePriorities", "IsActive",
                        IsActiveTree(), "SourceFrameNumber",
                        source_frame_number_);
-    scoped_ptr<OcclusionTracker<LayerImpl>> occlusion_tracker;
-    if (settings().use_occlusion_for_tile_prioritization) {
-      occlusion_tracker.reset(new OcclusionTracker<LayerImpl>(
-          root_layer()->render_surface()->content_rect()));
-      occlusion_tracker->set_minimum_tracking_size(
-          settings().minimum_occlusion_tracking_size);
-    }
-
-    bool resourceless_software_draw = (layer_tree_host_impl_->GetDrawMode() ==
-                                       DRAW_MODE_RESOURCELESS_SOFTWARE);
+    OcclusionTracker<LayerImpl> occlusion_tracker(
+        root_layer()->render_surface()->content_rect());
+    occlusion_tracker.set_minimum_tracking_size(
+        settings().minimum_occlusion_tracking_size);
 
     // LayerIterator is used here instead of CallFunctionForSubtree to only
     // UpdateTilePriorities on layers that will be visible (and thus have valid
     // draw properties) and not because any ordering is required.
-    typedef LayerIterator<LayerImpl> LayerIteratorType;
-    LayerIteratorType end = LayerIteratorType::End(&render_surface_layer_list_);
-    size_t layers_updated_count = 0;
-    bool tile_priorities_updated = false;
-    for (LayerIteratorType it =
-             LayerIteratorType::Begin(&render_surface_layer_list_);
-         it != end;
-         ++it) {
-      if (occlusion_tracker)
-        occlusion_tracker->EnterLayer(it);
-
-      LayerImpl* layer = *it;
-      const Occlusion& occlusion_in_content_space =
-          occlusion_tracker ? occlusion_tracker->GetCurrentOcclusionForLayer(
-                                  layer->draw_transform())
-                            : Occlusion();
+    auto end = LayerIterator<LayerImpl>::End(&render_surface_layer_list_);
+    for (auto it = LayerIterator<LayerImpl>::Begin(&render_surface_layer_list_);
+         it != end; ++it) {
+      occlusion_tracker.EnterLayer(it);
 
       if (it.represents_itself()) {
-        tile_priorities_updated |= layer->UpdateTiles(
-            occlusion_in_content_space, resourceless_software_draw);
-        ++layers_updated_count;
+        Occlusion occlusion =
+            occlusion_tracker.GetCurrentOcclusionForLayer(it->draw_transform());
+        it->draw_properties().occlusion_in_content_space = occlusion;
       }
 
-      if (!it.represents_contributing_render_surface()) {
-        if (occlusion_tracker)
-          occlusion_tracker->LeaveLayer(it);
-        continue;
+      if (it.represents_contributing_render_surface()) {
+        it->render_surface()->set_occlusion_in_content_space(
+            occlusion_tracker.GetCurrentOcclusionForContributingSurface(
+                it->render_surface()->draw_transform()));
+        it->render_surface()->set_replica_occlusion_in_content_space(
+            occlusion_tracker.GetCurrentOcclusionForContributingSurface(
+                it->render_surface()->replica_draw_transform()));
+        if (LayerImpl* mask = it->mask_layer()) {
+          mask->draw_properties().occlusion_in_content_space =
+              occlusion_tracker.GetCurrentOcclusionForContributingSurface(
+                  it->render_surface()->draw_transform() *

[vmpstr, 2015/02/13 00:24:54]

This is probably lack of knowledge for my part, but why is it that for a layer
we use it->draw_transform() but for a mask layer we use
render_surface->draw_transform() * it->draw_transform()?

[danakj, 2015/02/13 00:27:07]

The mask is used when drawing the surface, so I think it should have the same
occlusion as the surface, ie it should not be occluded by things inside the
surface.

[enne (OOO), 2015/02/13 00:30:23]

Occlusion on masks is not used anywhere, as it's redundant with the surface. 
(If you did use it, what would you do if the mask and surface disagreed?)

I'd say to just leave the mask occlusion unset / totally unoccluded.

+                  it->draw_transform());
+        }
+        if (it->replica_layer()) {
+          if (LayerImpl* mask = it->replica_layer()->mask_layer()) {
+            mask->draw_properties().occlusion_in_content_space =
+                occlusion_tracker.GetCurrentOcclusionForContributingSurface(
+                    it->render_surface()->replica_draw_transform() *
+                    it->draw_transform());
+          }
+        }
       }
 
-      if (layer->mask_layer()) {
-        tile_priorities_updated |= layer->mask_layer()->UpdateTiles(
-            occlusion_in_content_space, resourceless_software_draw);
-        ++layers_updated_count;
-      }
-      if (layer->replica_layer() && layer->replica_layer()->mask_layer()) {
-        tile_priorities_updated |=
-            layer->replica_layer()->mask_layer()->UpdateTiles(
-                occlusion_in_content_space, resourceless_software_draw);
-        ++layers_updated_count;
-      }
+      occlusion_tracker.LeaveLayer(it);
+    }
 
-      if (occlusion_tracker)
-        occlusion_tracker->LeaveLayer(it);
+    unoccluded_screen_space_region_ =
+        occlusion_tracker.ComputeVisibleRegionInScreen();
+
+    const bool resourceless_software_draw =
+        (layer_tree_host_impl_->GetDrawMode() ==
+         DRAW_MODE_RESOURCELESS_SOFTWARE);
+    static const Occlusion kEmptyOcclusion;
+    size_t layers_updated_count = 0;
+    bool tile_priorities_updated = false;
+    for (PictureLayerImpl* layer : picture_layers_) {
+      // TODO(danakj): Remove this to fix crbug.com/446751
+      if (!layer->IsDrawnRenderSurfaceLayerListMember())
+        continue;
+      ++layers_updated_count;
+      const Occlusion& occlusion =
+          settings().use_occlusion_for_tile_prioritization
+              ? layer->draw_properties().occlusion_in_content_space
+              : kEmptyOcclusion;
+      tile_priorities_updated |=
+          layer->UpdateTiles(occlusion, resourceless_software_draw);

[vmpstr, 2015/02/13 00:24:54]

mask and replica mask also need update tiles, right?

     }
 
     if (tile_priorities_updated)
@@ -657,6 +665,13 @@ const LayerImplList& LayerTreeImpl::RenderSurfaceLayerList() const {
   return render_surface_layer_list_;
 }
 
+const Region& LayerTreeImpl::UnoccludedScreenSpaceRegion() const {
+  // If this assert triggers, then the render_surface_layer_list_ is dirty, so
+  // the unoccluded_screen_space_region_ is not valid anymore.
+  DCHECK(!needs_update_draw_properties_);
+  return unoccluded_screen_space_region_;
+}
+
 gfx::Size LayerTreeImpl::ScrollableSize() const {
   LayerImpl* root_scroll_layer = OuterViewportScrollLayer()
                                      ? OuterViewportScrollLayer()