cc: Avoid redraw for missing tile outside visible rect

cc/layers/picture_layer_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/picture_layer_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/debug/trace_event_argument.h"
@@ skipping 247 matching lines @@
                                 visible_geometry_rect,
                                 color,
                                 width);
     }
   }
 
   // Keep track of the tilings that were used so that tilings that are
   // unused can be considered for removal.
   std::vector<PictureLayerTiling*> seen_tilings;
 
+  // Ignore missing tiles outside of viewport for tile priority. This is
+  // normally the same as draw viewport but can be independently overridden by
+  // embedders like Android WebView with SetExternalDrawConstraints.
+  gfx::Rect scaled_viewport_for_tile_priority = gfx::ScaleToEnclosingRect(
+      GetViewportForTilePriorityInContentSpace(), max_contents_scale);
+
   size_t missing_tile_count = 0u;
   size_t on_demand_missing_tile_count = 0u;
   for (PictureLayerTilingSet::CoverageIterator iter(tilings_.get(),
                                                     max_contents_scale,
                                                     scaled_visible_content_rect,
                                                     ideal_contents_scale_);
        iter;
        ++iter) {
     gfx::Rect geometry_rect = iter.geometry_rect();
     gfx::Rect visible_geometry_rect = occlusion_tracker.UnoccludedContentRect(
         geometry_rect, scaled_draw_transform);
     if (visible_geometry_rect.IsEmpty())
       continue;
 
     append_quads_data->visible_content_area +=
         visible_geometry_rect.width() * visible_geometry_rect.height();
 
     if (*iter && iter->IsReadyToDraw()) {
       const ManagedTileState::TileVersion& tile_version =
           iter->GetTileVersionForDrawing();
       switch (tile_version.mode()) {
         case ManagedTileState::TileVersion::RESOURCE_MODE: {
           gfx::RectF texture_rect = iter.texture_rect();
           gfx::Rect opaque_rect = iter->opaque_rect();
           opaque_rect.Intersect(geometry_rect);
 
-          if (iter->contents_scale() != ideal_contents_scale_)
+          if (iter->contents_scale() != ideal_contents_scale_ &&
+              geometry_rect.Intersects(scaled_viewport_for_tile_priority)) {
             append_quads_data->num_incomplete_tiles++;
+          }
 
           TileDrawQuad* quad =
               render_pass->CreateAndAppendDrawQuad<TileDrawQuad>();
           quad->SetNew(shared_quad_state,
                        geometry_rect,
                        opaque_rect,
                        visible_geometry_rect,
                        tile_version.get_resource_id(),
                        texture_rect,
                        iter.texture_size(),
@@ skipping 52 matching lines @@
         SkColor color = SafeOpaqueBackgroundColor();
         SolidColorDrawQuad* quad =
             render_pass->CreateAndAppendDrawQuad<SolidColorDrawQuad>();
         quad->SetNew(shared_quad_state,
                      geometry_rect,
                      visible_geometry_rect,
                      color,
                      false);
       }
 
-      append_quads_data->num_missing_tiles++;
+      if (geometry_rect.Intersects(scaled_viewport_for_tile_priority)) {
+        append_quads_data->num_missing_tiles++;
+        ++missing_tile_count;
+      }
       append_quads_data->approximated_visible_content_area +=
           visible_geometry_rect.width() * visible_geometry_rect.height();
-      ++missing_tile_count;
       continue;
     }
 
     if (iter->priority(ACTIVE_TREE).resolution != HIGH_RESOLUTION) {
       append_quads_data->approximated_visible_content_area +=
           visible_geometry_rect.width() * visible_geometry_rect.height();
     }
 
     if (seen_tilings.empty() || seen_tilings.back() != iter.CurrentTiling())
       seen_tilings.push_back(iter.CurrentTiling());
@@ skipping 84 matching lines @@
   for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
     if (tilings_->tiling_at(i)->NeedsUpdateForFrameAtTime(
             current_frame_time_in_seconds)) {
       tiling_needs_update = true;
       break;
     }
   }
   if (!tiling_needs_update)
     return;
 
+  gfx::Rect visible_rect_in_content_space(
+      GetViewportForTilePriorityInContentSpace());
+  visible_rect_in_content_space.Intersect(visible_content_rect());
+  gfx::Rect visible_layer_rect = gfx::ScaleToEnclosingRect(
+      visible_rect_in_content_space, 1.f / contents_scale_x());
+  WhichTree tree =
+      layer_tree_impl()->IsActiveTree() ? ACTIVE_TREE : PENDING_TREE;
+  for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
+    tilings_->tiling_at(i)->UpdateTilePriorities(tree,
+                                                 visible_layer_rect,
+                                                 ideal_contents_scale_,
+                                                 current_frame_time_in_seconds,
+                                                 occlusion_tracker,
+                                                 render_target(),
+                                                 draw_transform());
+  }
+
+  // Tile priorities were modified.
+  layer_tree_impl()->DidModifyTilePriorities();
+}
+
+gfx::Rect PictureLayerImpl::GetViewportForTilePriorityInContentSpace() const {
   // If visible_rect_for_tile_priority_ is empty or
   // viewport_rect_for_tile_priority_ is set to be different from the device
   // viewport, try to inverse project the viewport into layer space and use
   // that. Otherwise just use visible_rect_for_tile_priority_
   gfx::Rect visible_rect_in_content_space = visible_rect_for_tile_priority_;
 
   if (visible_rect_in_content_space.IsEmpty() ||
       layer_tree_impl()->DeviceViewport() != viewport_rect_for_tile_priority_) {
     gfx::Transform view_to_layer(gfx::Transform::kSkipInitialization);
 
     if (screen_space_transform_for_tile_priority_.GetInverse(&view_to_layer)) {
       // Transform from view space to content space.
       visible_rect_in_content_space =
           gfx::ToEnclosingRect(MathUtil::ProjectClippedRect(
               view_to_layer, viewport_rect_for_tile_priority_));
 
       visible_rect_in_content_space.Intersect(gfx::Rect(content_bounds()));
     }
   }
 
-  gfx::Rect visible_layer_rect = gfx::ScaleToEnclosingRect(
-      visible_rect_in_content_space, 1.f / contents_scale_x());
-  WhichTree tree =
-      layer_tree_impl()->IsActiveTree() ? ACTIVE_TREE : PENDING_TREE;
-  for (size_t i = 0; i < tilings_->num_tilings(); ++i) {
-    tilings_->tiling_at(i)->UpdateTilePriorities(tree,
-                                                 visible_layer_rect,
-                                                 ideal_contents_scale_,
-                                                 current_frame_time_in_seconds,
-                                                 occlusion_tracker,
-                                                 render_target(),
-                                                 draw_transform());
-  }
-
-  // Tile priorities were modified.
-  layer_tree_impl()->DidModifyTilePriorities();
+  return visible_rect_in_content_space;
 }
 
 void PictureLayerImpl::NotifyTileStateChanged(const Tile* tile) {
   if (layer_tree_impl()->IsActiveTree()) {
     gfx::RectF layer_damage_rect =
         gfx::ScaleRect(tile->content_rect(), 1.f / tile->contents_scale());
     AddDamageRect(layer_damage_rect);
   }
 }
 
@@ skipping 237 matching lines @@
   // The goal of this function is to find the minimum set of tiles that need to
   // be ready to draw in order to activate without flashing content from a
   // higher res on the active tree to a lower res on the pending tree.
 
   // First, early out for layers with no visible content.
   if (visible_content_rect().IsEmpty())
     return;
 
   gfx::Rect rect(visible_content_rect());
 
+  // Only mark tiles inside the viewport for tile priority as required for
+  // activation. This viewport is normally the same as the draw viewport but
+  // can be independently overridden by embedders like Android WebView with
+  // SetExternalDrawConstraints.
+  rect.Intersect(GetViewportForTilePriorityInContentSpace());
+
   float min_acceptable_scale =
       std::min(raster_contents_scale_, ideal_contents_scale_);
 
   if (PictureLayerImpl* twin = twin_layer_) {
     float twin_min_acceptable_scale =
         std::min(twin->ideal_contents_scale_, twin->raster_contents_scale_);
     // Ignore 0 scale in case CalculateContentsScale() has never been
     // called for active twin.
     if (twin_min_acceptable_scale != 0.0f) {
       min_acceptable_scale =
@@ skipping 918 matching lines @@
       PictureLayerTilingSet::TilingRange tiling_range = CurrentTilingRange();
       size_t current_tiling_range_offset = current_tiling_ - tiling_range.start;
       return tiling_range.end - 1 - current_tiling_range_offset;
     }
   }
   NOTREACHED();
   return 0;
 }
 
 }  // namespace cc