cc: Simplify picture layer tiling update tile priorities.

cc/resources/picture_layer_tiling.cc

Index: cc/resources/picture_layer_tiling.cc
diff --git a/cc/resources/picture_layer_tiling.cc b/cc/resources/picture_layer_tiling.cc
index cfab6f25c852b97040c36488cceffa89abc790c1..939e0b163d4a459aa50d0437a9aec5b94c2f8230 100644
--- a/cc/resources/picture_layer_tiling.cc
+++ b/cc/resources/picture_layer_tiling.cc
@@ -339,223 +339,154 @@ void PictureLayerTiling::Reset() {
   tiles_.clear();
 }
 
+gfx::Rect PictureLayerTiling::ComputeSkewport(
+    double current_frame_time_in_seconds,
+    const gfx::Rect& visible_rect_in_content_space) const {
+  gfx::Rect skewport = visible_rect_in_content_space;
+  if (last_impl_frame_time_in_seconds_ == 0.0)
+    return skewport;
+
+  double time_delta =
+      current_frame_time_in_seconds - last_impl_frame_time_in_seconds_;
+  if (time_delta == 0.0)
+    return skewport;
+
+  float skewport_target_time_in_seconds =
+      client_->GetSkewportTargetTimeInSeconds();
+  double extrapolation_multiplier =
+      skewport_target_time_in_seconds / time_delta;
+
+  int old_x = last_visible_rect_in_content_space_.x();
+  int old_y = last_visible_rect_in_content_space_.y();
+  int old_right = last_visible_rect_in_content_space_.right();
+  int old_bottom = last_visible_rect_in_content_space_.bottom();
+
+  int new_x = visible_rect_in_content_space.x();
+  int new_y = visible_rect_in_content_space.y();
+  int new_right = visible_rect_in_content_space.right();
+  int new_bottom = visible_rect_in_content_space.bottom();
+
+  int skewport_limit = client_->GetSkewportExtrapolationLimitInContentPixels();
+
+  // Compute the maximum skewport based on |skewport_limit|.
+  gfx::Rect max_skewport = skewport;
+  max_skewport.Inset(
+      -skewport_limit, -skewport_limit, -skewport_limit, -skewport_limit);
+
+  // Inset the skewport by the needed adjustment.
+  skewport.Inset(extrapolation_multiplier * (new_x - old_x),
+                 extrapolation_multiplier * (new_y - old_y),
+                 extrapolation_multiplier * (old_right - new_right),
+                 extrapolation_multiplier * (old_bottom - new_bottom));
+
+  // Clip the skewport to |max_skewport|.
+  skewport.Intersect(max_skewport);
+
+  // Finally, ensure that visible rect is contained in the skewport.
+  skewport.Union(visible_rect_in_content_space);
+  return skewport;
+}
+
 void PictureLayerTiling::UpdateTilePriorities(
     WhichTree tree,
-    const gfx::Size& device_viewport,
-    const gfx::Rect& viewport_in_layer_space,
     const gfx::Rect& visible_layer_rect,
-    const gfx::Size& last_layer_bounds,
-    const gfx::Size& current_layer_bounds,
-    float last_layer_contents_scale,
-    float current_layer_contents_scale,
-    const gfx::Transform& last_screen_transform,
-    const gfx::Transform& current_screen_transform,
-    double current_frame_time_in_seconds,
-    size_t max_tiles_for_interest_area) {
+    float layer_contents_scale,
+    double current_frame_time_in_seconds) {
   if (!NeedsUpdateForFrameAtTime(current_frame_time_in_seconds)) {
     // This should never be zero for the purposes of has_ever_been_updated().
     DCHECK_NE(current_frame_time_in_seconds, 0.0);
     return;
   }
+
+  gfx::Rect visible_rect_in_content_space =
+      gfx::ScaleToEnclosingRect(visible_layer_rect, contents_scale_);
+
   if (ContentRect().IsEmpty()) {
     last_impl_frame_time_in_seconds_ = current_frame_time_in_seconds;
+    last_visible_rect_in_content_space_ = visible_rect_in_content_space;
     return;
   }
 
-  gfx::Rect viewport_in_content_space =
-      gfx::ScaleToEnclosingRect(viewport_in_layer_space, contents_scale_);
-  gfx::Rect visible_content_rect =
-      gfx::ScaleToEnclosingRect(visible_layer_rect, contents_scale_);
+  size_t max_tiles_for_interest_area = client_->GetMaxTilesForInterestArea();
 
   gfx::Size tile_size = tiling_data_.max_texture_size();
-  int64 interest_rect_area =
+  int64 eventually_rect_area =
       max_tiles_for_interest_area * tile_size.width() * tile_size.height();
 
-  gfx::Rect starting_rect = visible_content_rect.IsEmpty()
-                            ? viewport_in_content_space
-                            : visible_content_rect;
-  gfx::Rect interest_rect = ExpandRectEquallyToAreaBoundedBy(
-      starting_rect,
-      interest_rect_area,
-      ContentRect(),
-      &expansion_cache_);
-  DCHECK(interest_rect.IsEmpty() ||
-         ContentRect().Contains(interest_rect));
-
-  SetLiveTilesRect(interest_rect);
-
-  double time_delta = 0;
-  if (last_impl_frame_time_in_seconds_ != 0.0 &&
-      last_layer_bounds == current_layer_bounds) {
-    time_delta =
-        current_frame_time_in_seconds - last_impl_frame_time_in_seconds_;
+  gfx::Rect skewport = ComputeSkewport(current_frame_time_in_seconds,
+                                       visible_rect_in_content_space);
+  DCHECK(skewport.Contains(visible_rect_in_content_space));
+
+  gfx::Rect eventually_rect =
+      ExpandRectEquallyToAreaBoundedBy(visible_rect_in_content_space,
+                                       eventually_rect_area,
+                                       ContentRect(),
+                                       &expansion_cache_);
+
+  DCHECK(eventually_rect.IsEmpty() || ContentRect().Contains(eventually_rect));
+
+  SetLiveTilesRect(eventually_rect);
+
+  last_impl_frame_time_in_seconds_ = current_frame_time_in_seconds;
+  last_visible_rect_in_content_space_ = visible_rect_in_content_space;
+
+  // Assign now priority to all visible tiles.
+  TilePriority now_priority(resolution_, TilePriority::NOW, 0);
+  for (TilingData::Iterator iter(&tiling_data_, visible_rect_in_content_space);
+       iter;
+       ++iter) {
+    TileMap::iterator find = tiles_.find(iter.index());
+    if (find == tiles_.end())
+      continue;
+    Tile* tile = find->second.get();
+
+    tile->SetPriority(tree, now_priority);
   }
 
-  gfx::RectF view_rect(device_viewport);
-  float current_scale = current_layer_contents_scale / contents_scale_;
-  float last_scale = last_layer_contents_scale / contents_scale_;
-
-  // Fast path tile priority calculation when both transforms are translations.
-  if (last_screen_transform.IsApproximatelyIdentityOrTranslation(
-          std::numeric_limits<float>::epsilon()) &&
-      current_screen_transform.IsApproximatelyIdentityOrTranslation(
-          std::numeric_limits<float>::epsilon())) {
-    gfx::Vector2dF current_offset(
-        current_screen_transform.matrix().get(0, 3),
-        current_screen_transform.matrix().get(1, 3));
-    gfx::Vector2dF last_offset(
-        last_screen_transform.matrix().get(0, 3),
-        last_screen_transform.matrix().get(1, 3));
-
-    for (TilingData::Iterator iter(&tiling_data_, interest_rect);
-         iter; ++iter) {
-      TileMap::iterator find = tiles_.find(iter.index());
-      if (find == tiles_.end())
-        continue;
-      Tile* tile = find->second.get();
-
-      gfx::Rect tile_bounds =
-          tiling_data_.TileBounds(iter.index_x(), iter.index_y());
-      gfx::RectF current_screen_rect = gfx::ScaleRect(
-          tile_bounds,
-          current_scale,
-          current_scale) + current_offset;
-      gfx::RectF last_screen_rect = gfx::ScaleRect(
-          tile_bounds,
-          last_scale,
-          last_scale) + last_offset;
-
-      float distance_to_visible_in_pixels =
-          current_screen_rect.ManhattanInternalDistance(view_rect);
-
-      float time_to_visible_in_seconds =
-          TilePriority::TimeForBoundsToIntersect(
-              last_screen_rect, current_screen_rect, time_delta, view_rect);
-      TilePriority priority(
-          resolution_,
-          time_to_visible_in_seconds,
-          distance_to_visible_in_pixels);
-      tile->SetPriority(tree, priority);
-    }
-  } else if (!last_screen_transform.HasPerspective() &&
-             !current_screen_transform.HasPerspective()) {
-    // Secondary fast path that can be applied for any affine transforms.
-
-    // Initialize the necessary geometry in screen space, so that we can
-    // iterate over tiles in screen space without needing a costly transform
-    // mapping for each tile.
-
-    // Apply screen space transform to the local origin point (0, 0); only the
-    // translation component is needed and can be initialized directly.
-    gfx::Point current_screen_space_origin(
-        current_screen_transform.matrix().get(0, 3),
-        current_screen_transform.matrix().get(1, 3));
-
-    gfx::Point last_screen_space_origin(
-        last_screen_transform.matrix().get(0, 3),
-        last_screen_transform.matrix().get(1, 3));
-
-    float current_tile_width = tiling_data_.TileSizeX(0) * current_scale;
-    float last_tile_width = tiling_data_.TileSizeX(0) * last_scale;
-    float current_tile_height = tiling_data_.TileSizeY(0) * current_scale;
-    float last_tile_height = tiling_data_.TileSizeY(0) * last_scale;
-
-    // Apply screen space transform to local basis vectors (tile_width, 0) and
-    // (0, tile_height); the math simplifies and can be initialized directly.
-    gfx::Vector2dF current_horizontal(
-        current_screen_transform.matrix().get(0, 0) * current_tile_width,
-        current_screen_transform.matrix().get(1, 0) * current_tile_width);
-    gfx::Vector2dF current_vertical(
-        current_screen_transform.matrix().get(0, 1) * current_tile_height,
-        current_screen_transform.matrix().get(1, 1) * current_tile_height);
-
-    gfx::Vector2dF last_horizontal(
-        last_screen_transform.matrix().get(0, 0) * last_tile_width,
-        last_screen_transform.matrix().get(1, 0) * last_tile_width);
-    gfx::Vector2dF last_vertical(
-        last_screen_transform.matrix().get(0, 1) * last_tile_height,
-        last_screen_transform.matrix().get(1, 1) * last_tile_height);
-
-    for (TilingData::Iterator iter(&tiling_data_, interest_rect);
-         iter; ++iter) {
-      TileMap::iterator find = tiles_.find(iter.index());
-      if (find == tiles_.end())
-        continue;
+  // Assign soon priority to all tiles in the skewport that are not visible.
+  float content_to_screen_scale =
+      1.0f / (contents_scale_ * layer_contents_scale);
+  for (TilingData::DifferenceIterator iter(
+           &tiling_data_, skewport, visible_rect_in_content_space);
+       iter;
+       ++iter) {
+    TileMap::iterator find = tiles_.find(iter.index());
+    if (find == tiles_.end())
+      continue;
+    Tile* tile = find->second.get();
 
-      Tile* tile = find->second.get();
-
-      int i = iter.index_x();
-      int j = iter.index_y();
-      gfx::PointF current_tile_origin = current_screen_space_origin +
-              ScaleVector2d(current_horizontal, i) +
-              ScaleVector2d(current_vertical, j);
-      gfx::PointF last_tile_origin = last_screen_space_origin +
-              ScaleVector2d(last_horizontal, i) +
-              ScaleVector2d(last_vertical, j);
-
-      gfx::RectF current_screen_rect = gfx::QuadF(
-          current_tile_origin,
-          current_tile_origin + current_horizontal,
-          current_tile_origin + current_horizontal + current_vertical,
-          current_tile_origin + current_vertical).BoundingBox();
-
-      gfx::RectF last_screen_rect = gfx::QuadF(
-          last_tile_origin,
-          last_tile_origin + last_horizontal,
-          last_tile_origin + last_horizontal + last_vertical,
-          last_tile_origin + last_vertical).BoundingBox();
-
-      float distance_to_visible_in_pixels =
-          current_screen_rect.ManhattanInternalDistance(view_rect);
-
-      float time_to_visible_in_seconds =
-          TilePriority::TimeForBoundsToIntersect(
-              last_screen_rect, current_screen_rect, time_delta, view_rect);
-      TilePriority priority(
-          resolution_,
-          time_to_visible_in_seconds,
-          distance_to_visible_in_pixels);
-      tile->SetPriority(tree, priority);
-    }
-  } else {
-    for (TilingData::Iterator iter(&tiling_data_, interest_rect);
-         iter; ++iter) {
-      TileMap::iterator find = tiles_.find(iter.index());
-      if (find == tiles_.end())
-        continue;
-      Tile* tile = find->second.get();
-
-      gfx::Rect tile_bounds =
-          tiling_data_.TileBounds(iter.index_x(), iter.index_y());
-      gfx::RectF current_layer_content_rect = gfx::ScaleRect(
-          tile_bounds,
-          current_scale,
-          current_scale);
-      gfx::RectF current_screen_rect = MathUtil::MapClippedRect(
-          current_screen_transform, current_layer_content_rect);
-      gfx::RectF last_layer_content_rect = gfx::ScaleRect(
-          tile_bounds,
-          last_scale,
-          last_scale);
-      gfx::RectF last_screen_rect  = MathUtil::MapClippedRect(
-          last_screen_transform, last_layer_content_rect);
-
-      float distance_to_visible_in_pixels =
-          current_screen_rect.ManhattanInternalDistance(view_rect);
-
-      float time_to_visible_in_seconds =
-          TilePriority::TimeForBoundsToIntersect(
-              last_screen_rect, current_screen_rect, time_delta, view_rect);
-
-      TilePriority priority(
-          resolution_,
-          time_to_visible_in_seconds,
-          distance_to_visible_in_pixels);
-      tile->SetPriority(tree, priority);
-    }
+    gfx::Rect tile_bounds =
+        tiling_data_.TileBounds(iter.index_x(), iter.index_y());
+
+    float distance_to_visible =
+        visible_rect_in_content_space.ManhattanInternalDistance(tile_bounds) *
+        content_to_screen_scale;
+
+    TilePriority priority(resolution_, TilePriority::SOON, distance_to_visible);
+    tile->SetPriority(tree, priority);
   }
 
-  last_impl_frame_time_in_seconds_ = current_frame_time_in_seconds;
+  // Assign eventually priority to all tiles in the eventually rect that are not
+  // in the skewport.
+  for (TilingData::DifferenceIterator iter(
+           &tiling_data_, eventually_rect, skewport);
+       iter;
+       ++iter) {
+    TileMap::iterator find = tiles_.find(iter.index());
+    if (find == tiles_.end())
+      continue;
+    Tile* tile = find->second.get();
+
+    gfx::Rect tile_bounds =
+        tiling_data_.TileBounds(iter.index_x(), iter.index_y());
+
+    float distance_to_visible =
+        visible_rect_in_content_space.ManhattanInternalDistance(tile_bounds) *
+        content_to_screen_scale;
+    TilePriority priority(
+        resolution_, TilePriority::EVENTUALLY, distance_to_visible);
+    tile->SetPriority(tree, priority);
+  }
 }
 
 void PictureLayerTiling::SetLiveTilesRect(