Implement multiple alternative services per origin.

[chromium-blink-merge.git] / cc / tiles / 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/tiles/picture_layer_tiling.h"

#include <algorithm>
#include <cmath>
#include <limits>
#include <set>

#include "base/containers/hash_tables.h"
#include "base/containers/small_map.h"
#include "base/logging.h"
#include "base/numerics/safe_conversions.h"
#include "base/trace_event/trace_event.h"
#include "base/trace_event/trace_event_argument.h"
#include "cc/base/math_util.h"
#include "cc/playback/raster_source.h"
#include "cc/tiles/prioritized_tile.h"
#include "cc/tiles/tile.h"
#include "cc/tiles/tile_priority.h"
#include "ui/gfx/geometry/point_conversions.h"
#include "ui/gfx/geometry/rect_conversions.h"
#include "ui/gfx/geometry/safe_integer_conversions.h"
#include "ui/gfx/geometry/size_conversions.h"

namespace cc {
namespace {

const float kSoonBorderDistanceViewportPercentage = 0.15f;
const float kMaxSoonBorderDistanceInScreenPixels = 312.f;

}  // namespace

scoped_ptr<PictureLayerTiling> PictureLayerTiling::Create(
    WhichTree tree,
    float contents_scale,
    scoped_refptr<RasterSource> raster_source,
    PictureLayerTilingClient* client,
    size_t max_tiles_for_interest_area,
    float skewport_target_time_in_seconds,
    int skewport_extrapolation_limit_in_content_pixels) {
  return make_scoped_ptr(new PictureLayerTiling(
      tree, contents_scale, raster_source, client, max_tiles_for_interest_area,
      skewport_target_time_in_seconds,
      skewport_extrapolation_limit_in_content_pixels));
}

PictureLayerTiling::PictureLayerTiling(
    WhichTree tree,
    float contents_scale,
    scoped_refptr<RasterSource> raster_source,
    PictureLayerTilingClient* client,
    size_t max_tiles_for_interest_area,
    float skewport_target_time_in_seconds,
    int skewport_extrapolation_limit_in_content_pixels)
    : max_tiles_for_interest_area_(max_tiles_for_interest_area),
      skewport_target_time_in_seconds_(skewport_target_time_in_seconds),
      skewport_extrapolation_limit_in_content_pixels_(
          skewport_extrapolation_limit_in_content_pixels),
      contents_scale_(contents_scale),
      client_(client),
      tree_(tree),
      raster_source_(raster_source),
      resolution_(NON_IDEAL_RESOLUTION),
      tiling_data_(gfx::Size(), gfx::Size(), kBorderTexels),
      can_require_tiles_for_activation_(false),
      current_content_to_screen_scale_(0.f),
      has_visible_rect_tiles_(false),
      has_skewport_rect_tiles_(false),
      has_soon_border_rect_tiles_(false),
      has_eventually_rect_tiles_(false),
      all_tiles_done_(true) {
  DCHECK(!raster_source->IsSolidColor());
  gfx::Size content_bounds = gfx::ToCeiledSize(
      gfx::ScaleSize(raster_source_->GetSize(), contents_scale));
  gfx::Size tile_size = client_->CalculateTileSize(content_bounds);

  DCHECK(!gfx::ToFlooredSize(gfx::ScaleSize(raster_source_->GetSize(),
                                            contents_scale)).IsEmpty())
      << "Tiling created with scale too small as contents become empty."
      << " Layer bounds: " << raster_source_->GetSize().ToString()
      << " Contents scale: " << contents_scale;

  tiling_data_.SetTilingSize(content_bounds);
  tiling_data_.SetMaxTextureSize(tile_size);
}

PictureLayerTiling::~PictureLayerTiling() {
}

// static
float PictureLayerTiling::CalculateSoonBorderDistance(
    const gfx::Rect& visible_rect_in_content_space,
    float content_to_screen_scale) {
  float max_dimension = std::max(visible_rect_in_content_space.width(),
                                 visible_rect_in_content_space.height());
  return std::min(
      kMaxSoonBorderDistanceInScreenPixels / content_to_screen_scale,
      max_dimension * kSoonBorderDistanceViewportPercentage);
}

Tile* PictureLayerTiling::CreateTile(int i, int j) {
  TileMapKey key(i, j);
  DCHECK(tiles_.find(key) == tiles_.end());

  gfx::Rect paint_rect = tiling_data_.TileBoundsWithBorder(i, j);
  gfx::Rect tile_rect = paint_rect;
  tile_rect.set_size(tiling_data_.max_texture_size());

  if (!raster_source_->CoversRect(tile_rect, contents_scale_))
    return nullptr;

  all_tiles_done_ = false;
  ScopedTilePtr tile = client_->CreateTile(contents_scale_, tile_rect);
  Tile* raw_ptr = tile.get();
  tile->set_tiling_index(i, j);
  tiles_.add(key, tile.Pass());
  return raw_ptr;
}

void PictureLayerTiling::CreateMissingTilesInLiveTilesRect() {
  bool include_borders = false;
  for (TilingData::Iterator iter(&tiling_data_, live_tiles_rect_,
                                 include_borders);
       iter; ++iter) {
    TileMapKey key(iter.index());
    TileMap::iterator find = tiles_.find(key);
    if (find != tiles_.end())
      continue;

    if (ShouldCreateTileAt(key.index_x, key.index_y))
      CreateTile(key.index_x, key.index_y);
  }
  VerifyLiveTilesRect(false);
}

void PictureLayerTiling::TakeTilesAndPropertiesFrom(
    PictureLayerTiling* pending_twin,
    const Region& layer_invalidation) {
  TRACE_EVENT0("cc", "TakeTilesAndPropertiesFrom");
  SetRasterSourceAndResize(pending_twin->raster_source_);

  RemoveTilesInRegion(layer_invalidation, false /* recreate tiles */);

  resolution_ = pending_twin->resolution_;
  bool create_missing_tiles = false;
  if (live_tiles_rect_.IsEmpty()) {
    live_tiles_rect_ = pending_twin->live_tiles_rect();
    create_missing_tiles = true;
  } else {
    SetLiveTilesRect(pending_twin->live_tiles_rect());
  }

  if (tiles_.empty()) {
    tiles_.swap(pending_twin->tiles_);
    all_tiles_done_ = pending_twin->all_tiles_done_;
  } else {
    while (!pending_twin->tiles_.empty()) {
      TileMapKey key = pending_twin->tiles_.begin()->first;
      tiles_.set(key, pending_twin->tiles_.take_and_erase(key));
    }
    all_tiles_done_ &= pending_twin->all_tiles_done_;
  }
  DCHECK(pending_twin->tiles_.empty());
  pending_twin->all_tiles_done_ = true;

  if (create_missing_tiles)
    CreateMissingTilesInLiveTilesRect();

  VerifyLiveTilesRect(false);

  SetTilePriorityRects(pending_twin->current_content_to_screen_scale_,
                       pending_twin->current_visible_rect_,
                       pending_twin->current_skewport_rect_,
                       pending_twin->current_soon_border_rect_,
                       pending_twin->current_eventually_rect_,
                       pending_twin->current_occlusion_in_layer_space_);
}

void PictureLayerTiling::SetRasterSourceAndResize(
    scoped_refptr<RasterSource> raster_source) {
  DCHECK(!raster_source->IsSolidColor());
  gfx::Size old_layer_bounds = raster_source_->GetSize();
  raster_source_.swap(raster_source);
  gfx::Size new_layer_bounds = raster_source_->GetSize();
  gfx::Size content_bounds =
      gfx::ToCeiledSize(gfx::ScaleSize(new_layer_bounds, contents_scale_));
  gfx::Size tile_size = client_->CalculateTileSize(content_bounds);

  if (tile_size != tiling_data_.max_texture_size()) {
    tiling_data_.SetTilingSize(content_bounds);
    tiling_data_.SetMaxTextureSize(tile_size);
    // When the tile size changes, the TilingData positions no longer work
    // as valid keys to the TileMap, so just drop all tiles and clear the live
    // tiles rect.
    Reset();
    return;
  }

  if (old_layer_bounds == new_layer_bounds)
    return;

  // The SetLiveTilesRect() method would drop tiles outside the new bounds,
  // but may do so incorrectly if resizing the tiling causes the number of
  // tiles in the tiling_data_ to change.
  gfx::Rect content_rect(content_bounds);
  int before_left = tiling_data_.TileXIndexFromSrcCoord(live_tiles_rect_.x());
  int before_top = tiling_data_.TileYIndexFromSrcCoord(live_tiles_rect_.y());
  int before_right =
      tiling_data_.TileXIndexFromSrcCoord(live_tiles_rect_.right() - 1);
  int before_bottom =
      tiling_data_.TileYIndexFromSrcCoord(live_tiles_rect_.bottom() - 1);

  // The live_tiles_rect_ is clamped to stay within the tiling size as we
  // change it.
  live_tiles_rect_.Intersect(content_rect);
  tiling_data_.SetTilingSize(content_bounds);

  int after_right = -1;
  int after_bottom = -1;
  if (!live_tiles_rect_.IsEmpty()) {
    after_right =
        tiling_data_.TileXIndexFromSrcCoord(live_tiles_rect_.right() - 1);
    after_bottom =
        tiling_data_.TileYIndexFromSrcCoord(live_tiles_rect_.bottom() - 1);
  }

  // There is no recycled twin since this is run on the pending tiling
  // during commit, and on the active tree during activate.
  // Drop tiles outside the new layer bounds if the layer shrank.
  for (int i = after_right + 1; i <= before_right; ++i) {
    for (int j = before_top; j <= before_bottom; ++j)
      RemoveTileAt(i, j);
  }
  for (int i = before_left; i <= after_right; ++i) {
    for (int j = after_bottom + 1; j <= before_bottom; ++j)
      RemoveTileAt(i, j);
  }

  if (after_right > before_right) {
    DCHECK_EQ(after_right, before_right + 1);
    for (int j = before_top; j <= after_bottom; ++j) {
      if (ShouldCreateTileAt(after_right, j))
        CreateTile(after_right, j);
    }
  }
  if (after_bottom > before_bottom) {
    DCHECK_EQ(after_bottom, before_bottom + 1);
    for (int i = before_left; i <= before_right; ++i) {
      if (ShouldCreateTileAt(i, after_bottom))
        CreateTile(i, after_bottom);
    }
  }
}

void PictureLayerTiling::Invalidate(const Region& layer_invalidation) {
  DCHECK_IMPLIES(tree_ == ACTIVE_TREE,
                 !client_->GetPendingOrActiveTwinTiling(this));
  RemoveTilesInRegion(layer_invalidation, true /* recreate tiles */);
}

void PictureLayerTiling::RemoveTilesInRegion(const Region& layer_invalidation,
                                             bool recreate_tiles) {
  // We only invalidate the active tiling when it's orphaned: it has no pending
  // twin, so it's slated for removal in the future.
  if (live_tiles_rect_.IsEmpty())
    return;
  // Pick 16 for the size of the SmallMap before it promotes to a hash_map.
  // 4x4 tiles should cover most small invalidations, and walking a vector of
  // 16 is fast enough. If an invalidation is huge we will fall back to a
  // hash_map instead of a vector in the SmallMap.
  base::SmallMap<base::hash_map<TileMapKey, gfx::Rect>, 16> remove_tiles;
  gfx::Rect expanded_live_tiles_rect =
      tiling_data_.ExpandRectIgnoringBordersToTileBounds(live_tiles_rect_);
  for (Region::Iterator iter(layer_invalidation); iter.has_rect();
       iter.next()) {
    gfx::Rect layer_rect = iter.rect();
    // The pixels which are invalid in content space.
    gfx::Rect invalid_content_rect =
        gfx::ScaleToEnclosingRect(layer_rect, contents_scale_);
    // Consider tiles inside the live tiles rect even if only their border
    // pixels intersect the invalidation. But don't consider tiles outside
    // the live tiles rect with the same conditions, as they won't exist.
    gfx::Rect coverage_content_rect = invalid_content_rect;
    int border_pixels = tiling_data_.border_texels();
    coverage_content_rect.Inset(-border_pixels, -border_pixels);
    // Avoid needless work by not bothering to invalidate where there aren't
    // tiles.
    coverage_content_rect.Intersect(expanded_live_tiles_rect);
    if (coverage_content_rect.IsEmpty())
      continue;
    // Since the content_rect includes border pixels already, don't include
    // borders when iterating to avoid double counting them.
    bool include_borders = false;
    for (TilingData::Iterator iter(&tiling_data_, coverage_content_rect,
                                   include_borders);
         iter; ++iter) {
      // This also adds the TileMapKey to the map.
      remove_tiles[TileMapKey(iter.index())].Union(invalid_content_rect);
    }
  }

  for (const auto& pair : remove_tiles) {
    const TileMapKey& key = pair.first;
    const gfx::Rect& invalid_content_rect = pair.second;
    // TODO(danakj): This old_tile will not exist if we are committing to a
    // pending tree since there is no tile there to remove, which prevents
    // tiles from knowing the invalidation rect and content id. crbug.com/490847
    ScopedTilePtr old_tile = TakeTileAt(key.index_x, key.index_y);
    if (recreate_tiles && old_tile) {
      if (Tile* tile = CreateTile(key.index_x, key.index_y))
        tile->SetInvalidated(invalid_content_rect, old_tile->id());
    }
  }
}

bool PictureLayerTiling::ShouldCreateTileAt(int i, int j) const {
  // Active tree should always create a tile. The reason for this is that active
  // tree represents content that we draw on screen, which means that whenever
  // we check whether a tile should exist somewhere, the answer is yes. This
  // doesn't mean it will actually be created (if raster source doesn't cover
  // the tile for instance). Pending tree, on the other hand, should only be
  // creating tiles that are different from the current active tree, which is
  // represented by the logic in the rest of the function.
  if (tree_ == ACTIVE_TREE)
    return true;

  // If the pending tree has no active twin, then it needs to create all tiles.
  const PictureLayerTiling* active_twin =
      client_->GetPendingOrActiveTwinTiling(this);
  if (!active_twin)
    return true;

  // Pending tree will override the entire active tree if indices don't match.
  if (!TilingMatchesTileIndices(active_twin))
    return true;

  gfx::Rect paint_rect = tiling_data_.TileBoundsWithBorder(i, j);
  gfx::Rect tile_rect = paint_rect;
  tile_rect.set_size(tiling_data_.max_texture_size());

  // If the active tree can't create a tile, because of its raster source, then
  // the pending tree should create one.
  if (!active_twin->raster_source()->CoversRect(tile_rect, contents_scale()))
    return true;

  const Region* layer_invalidation = client_->GetPendingInvalidation();
  gfx::Rect layer_rect =
      gfx::ScaleToEnclosingRect(tile_rect, 1.f / contents_scale());

  // If this tile is invalidated, then the pending tree should create one.
  if (layer_invalidation && layer_invalidation->Intersects(layer_rect))
    return true;

  // If the active tree doesn't have a tile here, but it's in the pending tree's
  // visible rect, then the pending tree should create a tile. This can happen
  // if the pending visible rect is outside of the active tree's live tiles
  // rect. In those situations, we need to block activation until we're ready to
  // display content, which will have to come from the pending tree.
  if (!active_twin->TileAt(i, j) && current_visible_rect_.Intersects(tile_rect))
    return true;

  // In all other cases, the pending tree doesn't need to create a tile.
  return false;
}

bool PictureLayerTiling::TilingMatchesTileIndices(
    const PictureLayerTiling* twin) const {
  return tiling_data_.max_texture_size() ==
         twin->tiling_data_.max_texture_size();
}

PictureLayerTiling::CoverageIterator::CoverageIterator()
    : tiling_(NULL),
      current_tile_(NULL),
      tile_i_(0),
      tile_j_(0),
      left_(0),
      top_(0),
      right_(-1),
      bottom_(-1) {
}

PictureLayerTiling::CoverageIterator::CoverageIterator(
    const PictureLayerTiling* tiling,
    float dest_scale,
    const gfx::Rect& dest_rect)
    : tiling_(tiling),
      dest_rect_(dest_rect),
      dest_to_content_scale_(0),
      current_tile_(NULL),
      tile_i_(0),
      tile_j_(0),
      left_(0),
      top_(0),
      right_(-1),
      bottom_(-1) {
  DCHECK(tiling_);
  if (dest_rect_.IsEmpty())
    return;

  dest_to_content_scale_ = tiling_->contents_scale_ / dest_scale;

  gfx::Rect content_rect =
      gfx::ScaleToEnclosingRect(dest_rect_,
                                dest_to_content_scale_,
                                dest_to_content_scale_);
  // IndexFromSrcCoord clamps to valid tile ranges, so it's necessary to
  // check for non-intersection first.
  content_rect.Intersect(gfx::Rect(tiling_->tiling_size()));
  if (content_rect.IsEmpty())
    return;

  left_ = tiling_->tiling_data_.TileXIndexFromSrcCoord(content_rect.x());
  top_ = tiling_->tiling_data_.TileYIndexFromSrcCoord(content_rect.y());
  right_ = tiling_->tiling_data_.TileXIndexFromSrcCoord(
      content_rect.right() - 1);
  bottom_ = tiling_->tiling_data_.TileYIndexFromSrcCoord(
      content_rect.bottom() - 1);

  tile_i_ = left_ - 1;
  tile_j_ = top_;
  ++(*this);
}

PictureLayerTiling::CoverageIterator::~CoverageIterator() {
}

PictureLayerTiling::CoverageIterator&
PictureLayerTiling::CoverageIterator::operator++() {
  if (tile_j_ > bottom_)
    return *this;

  bool first_time = tile_i_ < left_;
  bool new_row = false;
  tile_i_++;
  if (tile_i_ > right_) {
    tile_i_ = left_;
    tile_j_++;
    new_row = true;
    if (tile_j_ > bottom_) {
      current_tile_ = NULL;
      return *this;
    }
  }

  current_tile_ = tiling_->TileAt(tile_i_, tile_j_);

  // Calculate the current geometry rect.  Due to floating point rounding
  // and ToEnclosingRect, tiles might overlap in destination space on the
  // edges.
  gfx::Rect last_geometry_rect = current_geometry_rect_;

  gfx::Rect content_rect = tiling_->tiling_data_.TileBounds(tile_i_, tile_j_);

  current_geometry_rect_ =
      gfx::ScaleToEnclosingRect(content_rect,
                                1 / dest_to_content_scale_,
                                1 / dest_to_content_scale_);

  current_geometry_rect_.Intersect(dest_rect_);

  if (first_time)
    return *this;

  // Iteration happens left->right, top->bottom.  Running off the bottom-right
  // edge is handled by the intersection above with dest_rect_.  Here we make
  // sure that the new current geometry rect doesn't overlap with the last.
  int min_left;
  int min_top;
  if (new_row) {
    min_left = dest_rect_.x();
    min_top = last_geometry_rect.bottom();
  } else {
    min_left = last_geometry_rect.right();
    min_top = last_geometry_rect.y();
  }

  int inset_left = std::max(0, min_left - current_geometry_rect_.x());
  int inset_top = std::max(0, min_top - current_geometry_rect_.y());
  current_geometry_rect_.Inset(inset_left, inset_top, 0, 0);

  if (!new_row) {
    DCHECK_EQ(last_geometry_rect.right(), current_geometry_rect_.x());
    DCHECK_EQ(last_geometry_rect.bottom(), current_geometry_rect_.bottom());
    DCHECK_EQ(last_geometry_rect.y(), current_geometry_rect_.y());
  }

  return *this;
}

gfx::Rect PictureLayerTiling::CoverageIterator::geometry_rect() const {
  return current_geometry_rect_;
}

gfx::RectF PictureLayerTiling::CoverageIterator::texture_rect() const {
  gfx::PointF tex_origin =
      tiling_->tiling_data_.TileBoundsWithBorder(tile_i_, tile_j_).origin();

  // Convert from dest space => content space => texture space.
  gfx::RectF texture_rect(current_geometry_rect_);
  texture_rect.Scale(dest_to_content_scale_,
                     dest_to_content_scale_);
  texture_rect.Intersect(gfx::Rect(tiling_->tiling_size()));
  if (texture_rect.IsEmpty())
    return texture_rect;
  texture_rect.Offset(-tex_origin.OffsetFromOrigin());

  return texture_rect;
}

ScopedTilePtr PictureLayerTiling::TakeTileAt(int i, int j) {
  TileMap::iterator found = tiles_.find(TileMapKey(i, j));
  if (found == tiles_.end())
    return nullptr;
  return tiles_.take_and_erase(found);
}

bool PictureLayerTiling::RemoveTileAt(int i, int j) {
  TileMap::iterator found = tiles_.find(TileMapKey(i, j));
  if (found == tiles_.end())
    return false;
  tiles_.erase(found);
  return true;
}

void PictureLayerTiling::Reset() {
  live_tiles_rect_ = gfx::Rect();
  tiles_.clear();
  all_tiles_done_ = true;
}

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 (skewport.IsEmpty())
    return skewport;

  if (visible_rect_history_[1].frame_time_in_seconds == 0.0)
    return skewport;

  double time_delta = current_frame_time_in_seconds -
                      visible_rect_history_[1].frame_time_in_seconds;
  if (time_delta == 0.0)
    return skewport;

  double extrapolation_multiplier =
      skewport_target_time_in_seconds_ / time_delta;

  int old_x = visible_rect_history_[1].visible_rect_in_content_space.x();
  int old_y = visible_rect_history_[1].visible_rect_in_content_space.y();
  int old_right =
      visible_rect_history_[1].visible_rect_in_content_space.right();
  int old_bottom =
      visible_rect_history_[1].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();

  // Compute the maximum skewport based on
  // |skewport_extrapolation_limit_in_content_pixels_|.
  gfx::Rect max_skewport = skewport;
  max_skewport.Inset(-skewport_extrapolation_limit_in_content_pixels_,
                     -skewport_extrapolation_limit_in_content_pixels_);

  // 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));

  // Ensure that visible rect is contained in the skewport.
  skewport.Union(visible_rect_in_content_space);

  // Clip the skewport to |max_skewport|. This needs to happen after the
  // union in case intersecting would have left the empty rect.
  skewport.Intersect(max_skewport);

  // Due to limits in int's representation, it is possible that the two
  // operations above (union and intersect) result in an empty skewport. To
  // avoid any unpleasant situations like that, union the visible rect again to
  // ensure that skewport.Contains(visible_rect_in_content_space) is always
  // true.
  skewport.Union(visible_rect_in_content_space);

  return skewport;
}

bool PictureLayerTiling::ComputeTilePriorityRects(
    const gfx::Rect& viewport_in_layer_space,
    float ideal_contents_scale,
    double current_frame_time_in_seconds,
    const Occlusion& occlusion_in_layer_space) {
  // If we have, or had occlusions, mark the tiles as 'not done' to ensure that
  // we reiterate the tiles for rasterization.
  if (occlusion_in_layer_space.HasOcclusion() ||
      current_occlusion_in_layer_space_.HasOcclusion()) {
    set_all_tiles_done(false);
  }

  if (!NeedsUpdateForFrameAtTimeAndViewport(current_frame_time_in_seconds,
                                            viewport_in_layer_space)) {
    // This should never be zero for the purposes of has_ever_been_updated().
    DCHECK_NE(current_frame_time_in_seconds, 0.0);
    return false;
  }
  gfx::Rect visible_rect_in_content_space =
      gfx::ScaleToEnclosingRect(viewport_in_layer_space, contents_scale_);

  if (tiling_size().IsEmpty()) {
    UpdateVisibleRectHistory(current_frame_time_in_seconds,
                             visible_rect_in_content_space);
    last_viewport_in_layer_space_ = viewport_in_layer_space;
    return false;
  }

  // Calculate the skewport.
  gfx::Rect skewport = ComputeSkewport(current_frame_time_in_seconds,
                                       visible_rect_in_content_space);
  DCHECK(skewport.Contains(visible_rect_in_content_space));

  // Calculate the eventually/live tiles rect.
  gfx::Size tile_size = tiling_data_.max_texture_size();
  int64 eventually_rect_area =
      max_tiles_for_interest_area_ * tile_size.width() * tile_size.height();

  gfx::Rect eventually_rect =
      ExpandRectEquallyToAreaBoundedBy(visible_rect_in_content_space,
                                       eventually_rect_area,
                                       gfx::Rect(tiling_size()),
                                       &expansion_cache_);

  DCHECK(eventually_rect.IsEmpty() ||
         gfx::Rect(tiling_size()).Contains(eventually_rect))
      << "tiling_size: " << tiling_size().ToString()
      << " eventually_rect: " << eventually_rect.ToString();

  // Calculate the soon border rect.
  float content_to_screen_scale = ideal_contents_scale / contents_scale_;
  gfx::Rect soon_border_rect = visible_rect_in_content_space;
  float border = CalculateSoonBorderDistance(visible_rect_in_content_space,
                                             content_to_screen_scale);
  soon_border_rect.Inset(-border, -border, -border, -border);

  UpdateVisibleRectHistory(current_frame_time_in_seconds,
                           visible_rect_in_content_space);
  last_viewport_in_layer_space_ = viewport_in_layer_space;

  SetTilePriorityRects(content_to_screen_scale, visible_rect_in_content_space,
                       skewport, soon_border_rect, eventually_rect,
                       occlusion_in_layer_space);
  SetLiveTilesRect(eventually_rect);
  return true;
}

void PictureLayerTiling::SetTilePriorityRects(
    float content_to_screen_scale,
    const gfx::Rect& visible_rect_in_content_space,
    const gfx::Rect& skewport,
    const gfx::Rect& soon_border_rect,
    const gfx::Rect& eventually_rect,
    const Occlusion& occlusion_in_layer_space) {
  current_visible_rect_ = visible_rect_in_content_space;
  current_skewport_rect_ = skewport;
  current_soon_border_rect_ = soon_border_rect;
  current_eventually_rect_ = eventually_rect;
  current_occlusion_in_layer_space_ = occlusion_in_layer_space;
  current_content_to_screen_scale_ = content_to_screen_scale;

  gfx::Rect tiling_rect(tiling_size());
  has_visible_rect_tiles_ = tiling_rect.Intersects(current_visible_rect_);
  has_skewport_rect_tiles_ = tiling_rect.Intersects(current_skewport_rect_);
  has_soon_border_rect_tiles_ =
      tiling_rect.Intersects(current_soon_border_rect_);
  has_eventually_rect_tiles_ = tiling_rect.Intersects(current_eventually_rect_);
}

void PictureLayerTiling::SetLiveTilesRect(
    const gfx::Rect& new_live_tiles_rect) {
  DCHECK(new_live_tiles_rect.IsEmpty() ||
         gfx::Rect(tiling_size()).Contains(new_live_tiles_rect))
      << "tiling_size: " << tiling_size().ToString()
      << " new_live_tiles_rect: " << new_live_tiles_rect.ToString();
  if (live_tiles_rect_ == new_live_tiles_rect)
    return;

  // Iterate to delete all tiles outside of our new live_tiles rect.
  for (TilingData::DifferenceIterator iter(&tiling_data_, live_tiles_rect_,
                                           new_live_tiles_rect);
       iter; ++iter) {
    RemoveTileAt(iter.index_x(), iter.index_y());
  }

  // Iterate to allocate new tiles for all regions with newly exposed area.
  for (TilingData::DifferenceIterator iter(&tiling_data_, new_live_tiles_rect,
                                           live_tiles_rect_);
       iter; ++iter) {
    TileMapKey key(iter.index());
    if (ShouldCreateTileAt(key.index_x, key.index_y))
      CreateTile(key.index_x, key.index_y);
  }

  live_tiles_rect_ = new_live_tiles_rect;
  VerifyLiveTilesRect(false);
}

void PictureLayerTiling::VerifyLiveTilesRect(bool is_on_recycle_tree) const {
#if DCHECK_IS_ON()
  for (auto it = tiles_.begin(); it != tiles_.end(); ++it) {
    if (!it->second)
      continue;
    TileMapKey key = it->first;
    DCHECK(key.index_x < tiling_data_.num_tiles_x())
        << this << " " << key.index_x << "," << key.index_y << " num_tiles_x "
        << tiling_data_.num_tiles_x() << " live_tiles_rect "
        << live_tiles_rect_.ToString();
    DCHECK(key.index_y < tiling_data_.num_tiles_y())
        << this << " " << key.index_x << "," << key.index_y << " num_tiles_y "
        << tiling_data_.num_tiles_y() << " live_tiles_rect "
        << live_tiles_rect_.ToString();
    DCHECK(tiling_data_.TileBounds(key.index_x, key.index_y)
               .Intersects(live_tiles_rect_))
        << this << " " << key.index_x << "," << key.index_y << " tile bounds "
        << tiling_data_.TileBounds(key.index_x, key.index_y).ToString()
        << " live_tiles_rect " << live_tiles_rect_.ToString();
  }
#endif
}

bool PictureLayerTiling::IsTileOccluded(const Tile* tile) const {
  // If this tile is not occluded on this tree, then it is not occluded.
  if (!IsTileOccludedOnCurrentTree(tile))
    return false;

  // Otherwise, if this is the pending tree, we're done and the tile is
  // occluded.
  if (tree_ == PENDING_TREE)
    return true;

  // On the active tree however, we need to check if this tile will be
  // unoccluded upon activation, in which case it has to be considered
  // unoccluded.
  const PictureLayerTiling* pending_twin =
      client_->GetPendingOrActiveTwinTiling(this);
  if (pending_twin) {
    // If there's a pending tile in the same position. Or if the pending twin
    // would have to be creating all tiles, then we don't need to worry about
    // occlusion on the twin.
    if (!TilingMatchesTileIndices(pending_twin) ||
        pending_twin->TileAt(tile->tiling_i_index(), tile->tiling_j_index())) {
      return true;
    }
    return pending_twin->IsTileOccludedOnCurrentTree(tile);
  }
  return true;
}

bool PictureLayerTiling::IsTileOccludedOnCurrentTree(const Tile* tile) const {
  if (!current_occlusion_in_layer_space_.HasOcclusion())
    return false;
  gfx::Rect tile_query_rect =
      gfx::IntersectRects(tile->content_rect(), current_visible_rect_);
  // Explicitly check if the tile is outside the viewport. If so, we need to
  // return false, since occlusion for this tile is unknown.
  if (tile_query_rect.IsEmpty())
    return false;

  if (contents_scale_ != 1.f) {
    tile_query_rect =
        gfx::ScaleToEnclosingRect(tile_query_rect, 1.f / contents_scale_);
  }
  return current_occlusion_in_layer_space_.IsOccluded(tile_query_rect);
}

bool PictureLayerTiling::IsTileRequiredForActivation(const Tile* tile) const {
  if (tree_ == PENDING_TREE) {
    if (!can_require_tiles_for_activation_)
      return false;

    if (resolution_ != HIGH_RESOLUTION)
      return false;

    if (IsTileOccluded(tile))
      return false;

    bool tile_is_visible =
        tile->content_rect().Intersects(current_visible_rect_);
    if (!tile_is_visible)
      return false;

    if (client_->RequiresHighResToDraw())
      return true;

    const PictureLayerTiling* active_twin =
        client_->GetPendingOrActiveTwinTiling(this);
    if (!active_twin || !TilingMatchesTileIndices(active_twin))
      return true;

    if (active_twin->raster_source()->GetSize() != raster_source()->GetSize())
      return true;

    if (active_twin->current_visible_rect_ != current_visible_rect_)
      return true;

    Tile* twin_tile =
        active_twin->TileAt(tile->tiling_i_index(), tile->tiling_j_index());
    if (!twin_tile)
      return false;
    return true;
  }

  DCHECK_EQ(tree_, ACTIVE_TREE);
  const PictureLayerTiling* pending_twin =
      client_->GetPendingOrActiveTwinTiling(this);
  // If we don't have a pending tree, or the pending tree will overwrite the
  // given tile, then it is not required for activation.
  if (!pending_twin || !TilingMatchesTileIndices(pending_twin) ||
      pending_twin->TileAt(tile->tiling_i_index(), tile->tiling_j_index())) {
    return false;
  }
  // Otherwise, ask the pending twin if this tile is required for activation.
  return pending_twin->IsTileRequiredForActivation(tile);
}

bool PictureLayerTiling::IsTileRequiredForDraw(const Tile* tile) const {
  if (tree_ == PENDING_TREE)
    return false;

  if (resolution_ != HIGH_RESOLUTION)
    return false;

  bool tile_is_visible = current_visible_rect_.Intersects(tile->content_rect());
  if (!tile_is_visible)
    return false;

  if (IsTileOccludedOnCurrentTree(tile))
    return false;
  return true;
}

void PictureLayerTiling::UpdateRequiredStatesOnTile(Tile* tile) const {
  DCHECK(tile);
  tile->set_required_for_activation(IsTileRequiredForActivation(tile));
  tile->set_required_for_draw(IsTileRequiredForDraw(tile));
}

PrioritizedTile PictureLayerTiling::MakePrioritizedTile(
    Tile* tile,
    PriorityRectType priority_rect_type) const {
  DCHECK(tile);
  DCHECK(
      raster_source()->CoversRect(tile->content_rect(), tile->contents_scale()))
      << "Recording rect: "
      << gfx::ScaleToEnclosingRect(tile->content_rect(),
                                   1.f / tile->contents_scale()).ToString();

  return PrioritizedTile(tile, raster_source(),
                         ComputePriorityForTile(tile, priority_rect_type),
                         IsTileOccluded(tile));
}

std::map<const Tile*, PrioritizedTile>
PictureLayerTiling::UpdateAndGetAllPrioritizedTilesForTesting() const {
  std::map<const Tile*, PrioritizedTile> result;
  for (const auto& key_tile_pair : tiles_) {
    Tile* tile = key_tile_pair.second;
    UpdateRequiredStatesOnTile(tile);
    PrioritizedTile prioritized_tile =
        MakePrioritizedTile(tile, ComputePriorityRectTypeForTile(tile));
    result.insert(std::make_pair(prioritized_tile.tile(), prioritized_tile));
  }
  return result;
}

TilePriority PictureLayerTiling::ComputePriorityForTile(
    const Tile* tile,
    PriorityRectType priority_rect_type) const {
  // TODO(vmpstr): See if this can be moved to iterators.
  DCHECK_EQ(ComputePriorityRectTypeForTile(tile), priority_rect_type);
  DCHECK_EQ(TileAt(tile->tiling_i_index(), tile->tiling_j_index()), tile);

  TilePriority::PriorityBin priority_bin = client_->HasValidTilePriorities()
                                               ? TilePriority::NOW
                                               : TilePriority::EVENTUALLY;
  switch (priority_rect_type) {
    case VISIBLE_RECT:
      return TilePriority(resolution_, priority_bin, 0);
    case PENDING_VISIBLE_RECT:
      if (priority_bin < TilePriority::SOON)
        priority_bin = TilePriority::SOON;
      return TilePriority(resolution_, priority_bin, 0);
    case SKEWPORT_RECT:
    case SOON_BORDER_RECT:
      if (priority_bin < TilePriority::SOON)
        priority_bin = TilePriority::SOON;
      break;
    case EVENTUALLY_RECT:
      priority_bin = TilePriority::EVENTUALLY;
      break;
  }

  gfx::Rect tile_bounds =
      tiling_data_.TileBounds(tile->tiling_i_index(), tile->tiling_j_index());
  DCHECK_GT(current_content_to_screen_scale_, 0.f);
  float distance_to_visible =
      current_visible_rect_.ManhattanInternalDistance(tile_bounds) *
      current_content_to_screen_scale_;

  return TilePriority(resolution_, priority_bin, distance_to_visible);
}

PictureLayerTiling::PriorityRectType
PictureLayerTiling::ComputePriorityRectTypeForTile(const Tile* tile) const {
  DCHECK_EQ(TileAt(tile->tiling_i_index(), tile->tiling_j_index()), tile);
  gfx::Rect tile_bounds =
      tiling_data_.TileBounds(tile->tiling_i_index(), tile->tiling_j_index());

  if (current_visible_rect_.Intersects(tile_bounds))
    return VISIBLE_RECT;

  if (pending_visible_rect().Intersects(tile_bounds))
    return PENDING_VISIBLE_RECT;

  if (current_skewport_rect_.Intersects(tile_bounds))
    return SKEWPORT_RECT;

  if (current_soon_border_rect_.Intersects(tile_bounds))
    return SOON_BORDER_RECT;

  DCHECK(current_eventually_rect_.Intersects(tile_bounds));
  return EVENTUALLY_RECT;
}

void PictureLayerTiling::GetAllPrioritizedTilesForTracing(
    std::vector<PrioritizedTile>* prioritized_tiles) const {
  for (const auto& tile_pair : tiles_) {
    Tile* tile = tile_pair.second;
    prioritized_tiles->push_back(
        MakePrioritizedTile(tile, ComputePriorityRectTypeForTile(tile)));
  }
}

void PictureLayerTiling::AsValueInto(
    base::trace_event::TracedValue* state) const {
  state->SetInteger("num_tiles", base::saturated_cast<int>(tiles_.size()));
  state->SetDouble("content_scale", contents_scale_);
  MathUtil::AddToTracedValue("visible_rect", current_visible_rect_, state);
  MathUtil::AddToTracedValue("skewport_rect", current_skewport_rect_, state);
  MathUtil::AddToTracedValue("soon_rect", current_soon_border_rect_, state);
  MathUtil::AddToTracedValue("eventually_rect", current_eventually_rect_,
                             state);
  MathUtil::AddToTracedValue("tiling_size", tiling_size(), state);
}

size_t PictureLayerTiling::GPUMemoryUsageInBytes() const {
  size_t amount = 0;
  for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it) {
    const Tile* tile = it->second;
    amount += tile->GPUMemoryUsageInBytes();
  }
  return amount;
}

PictureLayerTiling::RectExpansionCache::RectExpansionCache()
  : previous_target(0) {
}

namespace {

// This struct represents an event at which the expending rect intersects
// one of its boundaries.  4 intersection events will occur during expansion.
struct EdgeEvent {
  enum { BOTTOM, TOP, LEFT, RIGHT } edge;
  int* num_edges;
  int distance;
};

// Compute the delta to expand from edges to cover target_area.
int ComputeExpansionDelta(int num_x_edges, int num_y_edges,
                          int width, int height,
                          int64 target_area) {
  // Compute coefficients for the quadratic equation:
  //   a*x^2 + b*x + c = 0
  int a = num_y_edges * num_x_edges;
  int b = num_y_edges * width + num_x_edges * height;
  int64 c = static_cast<int64>(width) * height - target_area;

  // Compute the delta for our edges using the quadratic equation.
  int delta =
      (a == 0) ? -c / b : (-b + static_cast<int>(std::sqrt(
                                    static_cast<int64>(b) * b - 4.0 * a * c))) /
                              (2 * a);
  return std::max(0, delta);
}

}  // namespace

gfx::Rect PictureLayerTiling::ExpandRectEquallyToAreaBoundedBy(
    const gfx::Rect& starting_rect,
    int64 target_area,
    const gfx::Rect& bounding_rect,
    RectExpansionCache* cache) {
  if (starting_rect.IsEmpty())
    return starting_rect;

  if (cache &&
      cache->previous_start == starting_rect &&
      cache->previous_bounds == bounding_rect &&
      cache->previous_target == target_area)
    return cache->previous_result;

  if (cache) {
    cache->previous_start = starting_rect;
    cache->previous_bounds = bounding_rect;
    cache->previous_target = target_area;
  }

  DCHECK(!bounding_rect.IsEmpty());
  DCHECK_GT(target_area, 0);

  // Expand the starting rect to cover target_area, if it is smaller than it.
  int delta = ComputeExpansionDelta(
      2, 2, starting_rect.width(), starting_rect.height(), target_area);
  gfx::Rect expanded_starting_rect = starting_rect;
  if (delta > 0)
    expanded_starting_rect.Inset(-delta, -delta);

  gfx::Rect rect = IntersectRects(expanded_starting_rect, bounding_rect);
  if (rect.IsEmpty()) {
    // The starting_rect and bounding_rect are far away.
    if (cache)
      cache->previous_result = rect;
    return rect;
  }
  if (delta >= 0 && rect == expanded_starting_rect) {
    // The starting rect already covers the entire bounding_rect and isn't too
    // large for the target_area.
    if (cache)
      cache->previous_result = rect;
    return rect;
  }

  // Continue to expand/shrink rect to let it cover target_area.

  // These values will be updated by the loop and uses as the output.
  int origin_x = rect.x();
  int origin_y = rect.y();
  int width = rect.width();
  int height = rect.height();

  // In the beginning we will consider 2 edges in each dimension.
  int num_y_edges = 2;
  int num_x_edges = 2;

  // Create an event list.
  EdgeEvent events[] = {
    { EdgeEvent::BOTTOM, &num_y_edges, rect.y() - bounding_rect.y() },
    { EdgeEvent::TOP, &num_y_edges, bounding_rect.bottom() - rect.bottom() },
    { EdgeEvent::LEFT, &num_x_edges, rect.x() - bounding_rect.x() },
    { EdgeEvent::RIGHT, &num_x_edges, bounding_rect.right() - rect.right() }
  };

  // Sort the events by distance (closest first).
  if (events[0].distance > events[1].distance) std::swap(events[0], events[1]);
  if (events[2].distance > events[3].distance) std::swap(events[2], events[3]);
  if (events[0].distance > events[2].distance) std::swap(events[0], events[2]);
  if (events[1].distance > events[3].distance) std::swap(events[1], events[3]);
  if (events[1].distance > events[2].distance) std::swap(events[1], events[2]);

  for (int event_index = 0; event_index < 4; event_index++) {
    const EdgeEvent& event = events[event_index];

    int delta = ComputeExpansionDelta(
        num_x_edges, num_y_edges, width, height, target_area);

    // Clamp delta to our event distance.
    if (delta > event.distance)
      delta = event.distance;

    // Adjust the edge count for this kind of edge.
    --*event.num_edges;

    // Apply the delta to the edges and edge events.
    for (int i = event_index; i < 4; i++) {
      switch (events[i].edge) {
        case EdgeEvent::BOTTOM:
            origin_y -= delta;
            height += delta;
            break;
        case EdgeEvent::TOP:
            height += delta;
            break;
        case EdgeEvent::LEFT:
            origin_x -= delta;
            width += delta;
            break;
        case EdgeEvent::RIGHT:
            width += delta;
            break;
      }
      events[i].distance -= delta;
    }

    // If our delta is less then our event distance, we're done.
    if (delta < event.distance)
      break;
  }

  gfx::Rect result(origin_x, origin_y, width, height);
  if (cache)
    cache->previous_result = result;
  return result;
}

}  // namespace cc