cc: Simplify picture layer tiling update tile priorities.

cc/resources/picture_layer_tiling.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/resources/picture_layer_tiling.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 
@@ skipping 321 matching lines @@
 
 gfx::Size PictureLayerTiling::CoverageIterator::texture_size() const {
   return tiling_->tiling_data_.max_texture_size();
 }
 
 void PictureLayerTiling::Reset() {
   live_tiles_rect_ = gfx::Rect();
   tiles_.clear();
 }
 
+gfx::Rect PictureLayerTiling::ComputeSkewport(

[epennerAtGoogle, 2014/02/03 23:43:03]

This could benefit from a high-level comment describing what this is doing (eg
This extrapolates each edge's location using it's velocity and the time elapsed
since last frame - except, it strictly grows and never shrinks).

Also, I think this needs a clamp on how much we extrapolate (using another
constant, unfortunately). If we are relying on finite differences, there is
problems with that type of velocity estimate that could result in massive
skewports.

Last, shrinking and growing viewports don't really change our priority ordering
within a layer. We would still just paint 'outwards'. However, a large skewport
might change how much memory we used compared to just sitting still on a page.
Maybe we should keep the larger skewport as it is here (it makes the most
sense), but if so I think we should limit the extra 'outwards' painting it
causes eventually (to make sure it doesn't spike our memory too much).

[vmpstr, 2014/02/04 19:50:49]

I added a comment in the header file.
I can buy the argument for limiting the skewport based on some constant (just
capping the extrapolation distance). I don't have a good sense of what we want
this constant to be though. Are you thinking here on the order of a few rows? Or
on the order of a few thousand pixels? I'd propose something like 2k pixels if
the choice is left up to me, which is what I've put in. Does that sound
reasonable?

+    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_width = last_visible_rect_in_content_space_.width();
+  int old_height = last_visible_rect_in_content_space_.height();
+  int old_x = last_visible_rect_in_content_space_.x();
+  int old_y = last_visible_rect_in_content_space_.y();
+
+  int new_width = visible_rect_in_content_space.width();
+  int new_height = visible_rect_in_content_space.height();
+  int new_x = visible_rect_in_content_space.x();
+  int new_y = visible_rect_in_content_space.y();
+
+  skewport.set_width(skewport.width() +
+                     extrapolation_multiplier * (new_width - old_width));
+  skewport.set_height(skewport.height() +
+                      extrapolation_multiplier * (new_height - old_height));
+  skewport.set_x(skewport.x() + extrapolation_multiplier * (new_x - old_x));
+  skewport.set_y(skewport.y() + extrapolation_multiplier * (new_y - old_y));
+  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));
+  gfx::Rect skewport = ComputeSkewport(current_frame_time_in_seconds,
+                                       visible_rect_in_content_space);
+  DCHECK(skewport.Contains(visible_rect_in_content_space));
 
-  SetLiveTilesRect(interest_rect);
+  gfx::Rect eventually_rect =
+      ExpandRectEquallyToAreaBoundedBy(visible_rect_in_content_space,
+                                       eventually_rect_area,
+                                       ContentRect(),
+                                       &expansion_cache_);
+  DCHECK(eventually_rect.IsEmpty() ||
+         ContentRect().Contains(eventually_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_;
+  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_;
+  // 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();
 
-  // 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));
+    gfx::Rect tile_bounds =
+        tiling_data_.TileBounds(iter.index_x(), iter.index_y());
 
-    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();
+    float distance_to_visible =
+        visible_rect_in_content_space.ManhattanInternalDistance(tile_bounds) *
+        content_to_screen_scale;
 
-      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;
-
-      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);
-    }
+    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(
     const gfx::Rect& new_live_tiles_rect) {
   DCHECK(new_live_tiles_rect.IsEmpty() ||
          ContentRect().Contains(new_live_tiles_rect));
   if (live_tiles_rect_ == new_live_tiles_rect)
     return;
 
   // Iterate to delete all tiles outside of our new live_tiles rect.
@@ skipping 217 matching lines @@
       break;
   }
 
   gfx::Rect result(origin_x, origin_y, width, height);
   if (cache)
     cache->previous_result = result;
   return result;
 }
 
 }  // namespace cc