path: root/chromium/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>

#include "base/debug/trace_event.h"
#include "cc/base/math_util.h"
#include "ui/gfx/point_conversions.h"
#include "ui/gfx/rect_conversions.h"
#include "ui/gfx/safe_integer_conversions.h"
#include "ui/gfx/size_conversions.h"

namespace cc {

scoped_ptr<PictureLayerTiling> PictureLayerTiling::Create(
    float contents_scale,
    gfx::Size layer_bounds,
    PictureLayerTilingClient* client) {
  return make_scoped_ptr(new PictureLayerTiling(contents_scale,
                                                layer_bounds,
                                                client));
}

PictureLayerTiling::PictureLayerTiling(float contents_scale,
                                       gfx::Size layer_bounds,
                                       PictureLayerTilingClient* client)
    : contents_scale_(contents_scale),
      layer_bounds_(layer_bounds),
      resolution_(NON_IDEAL_RESOLUTION),
      client_(client),
      tiling_data_(gfx::Size(), gfx::Size(), true),
      last_impl_frame_time_in_seconds_(0.0) {
  gfx::Size content_bounds =
      gfx::ToCeiledSize(gfx::ScaleSize(layer_bounds, contents_scale));
  gfx::Size tile_size = client_->CalculateTileSize(content_bounds);

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

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

PictureLayerTiling::~PictureLayerTiling() {
}

void PictureLayerTiling::SetClient(PictureLayerTilingClient* client) {
  client_ = client;
}

gfx::Rect PictureLayerTiling::ContentRect() const {
  return gfx::Rect(tiling_data_.total_size());
}

gfx::SizeF PictureLayerTiling::ContentSizeF() const {
  return gfx::ScaleSize(layer_bounds_, contents_scale_);
}

Tile* PictureLayerTiling::TileAt(int i, int j) const {
  TileMap::const_iterator iter = tiles_.find(TileMapKey(i, j));
  if (iter == tiles_.end())
    return NULL;
  return iter->second.get();
}

void PictureLayerTiling::CreateTile(int i,
                                    int j,
                                    const PictureLayerTiling* twin_tiling) {
  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());

  // Check our twin for a valid tile.
  if (twin_tiling &&
      tiling_data_.max_texture_size() ==
      twin_tiling->tiling_data_.max_texture_size()) {
    if (Tile* candidate_tile = twin_tiling->TileAt(i, j)) {
      gfx::Rect rect =
          gfx::ScaleToEnclosingRect(paint_rect, 1.0f / contents_scale_);
      if (!client_->GetInvalidation()->Intersects(rect)) {
        tiles_[key] = candidate_tile;
        return;
      }
    }
  }

  // Create a new tile because our twin didn't have a valid one.
  scoped_refptr<Tile> tile = client_->CreateTile(this, tile_rect);
  if (tile.get())
    tiles_[key] = tile;
}

Region PictureLayerTiling::OpaqueRegionInContentRect(
    gfx::Rect content_rect) const {
  Region opaque_region;
  // TODO(enne): implement me
  return opaque_region;
}

void PictureLayerTiling::SetCanUseLCDText(bool can_use_lcd_text) {
  for (TileMap::iterator it = tiles_.begin(); it != tiles_.end(); ++it)
    it->second->set_can_use_lcd_text(can_use_lcd_text);
}

void PictureLayerTiling::CreateMissingTilesInLiveTilesRect() {
  const PictureLayerTiling* twin_tiling = client_->GetTwinTiling(this);
  for (TilingData::Iterator iter(&tiling_data_, live_tiles_rect_); iter;
       ++iter) {
    TileMapKey key = iter.index();
    TileMap::iterator find = tiles_.find(key);
    if (find != tiles_.end())
      continue;
    CreateTile(key.first, key.second, twin_tiling);
  }
}

void PictureLayerTiling::SetLayerBounds(gfx::Size layer_bounds) {
  if (layer_bounds_ == layer_bounds)
    return;

  DCHECK(!layer_bounds.IsEmpty());

  gfx::Size old_layer_bounds = layer_bounds_;
  layer_bounds_ = layer_bounds;
  gfx::Size old_content_bounds = tiling_data_.total_size();
  gfx::Size content_bounds =
      gfx::ToCeiledSize(gfx::ScaleSize(layer_bounds_, contents_scale_));

  gfx::Size tile_size = client_->CalculateTileSize(content_bounds);
  if (tile_size != tiling_data_.max_texture_size()) {
    tiling_data_.SetTotalSize(content_bounds);
    tiling_data_.SetMaxTextureSize(tile_size);
    Reset();
    return;
  }

  // Any tiles outside our new bounds are invalid and should be dropped.
  gfx::Rect bounded_live_tiles_rect(live_tiles_rect_);
  bounded_live_tiles_rect.Intersect(gfx::Rect(content_bounds));
  SetLiveTilesRect(bounded_live_tiles_rect);
  tiling_data_.SetTotalSize(content_bounds);

  // Create tiles for newly exposed areas.
  Region layer_region((gfx::Rect(layer_bounds_)));
  layer_region.Subtract(gfx::Rect(old_layer_bounds));
  Invalidate(layer_region);
}

void PictureLayerTiling::Invalidate(const Region& layer_region) {
  std::vector<TileMapKey> new_tile_keys;
  for (Region::Iterator iter(layer_region); iter.has_rect(); iter.next()) {
    gfx::Rect layer_rect = iter.rect();
    gfx::Rect content_rect =
        gfx::ScaleToEnclosingRect(layer_rect, contents_scale_);
    content_rect.Intersect(live_tiles_rect_);
    if (content_rect.IsEmpty())
      continue;
    for (TilingData::Iterator iter(&tiling_data_, content_rect); iter; ++iter) {
      TileMapKey key(iter.index());
      TileMap::iterator find = tiles_.find(key);
      if (find == tiles_.end())
        continue;
      tiles_.erase(find);
      new_tile_keys.push_back(key);
    }
  }

  const PictureLayerTiling* twin_tiling = client_->GetTwinTiling(this);
  for (size_t i = 0; i < new_tile_keys.size(); ++i)
    CreateTile(new_tile_keys[i].first, new_tile_keys[i].second, twin_tiling);
}

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,
    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;
  // This is the maximum size that the dest rect can be, given the content size.
  gfx::Size dest_content_size = gfx::ToCeiledSize(gfx::ScaleSize(
      tiling_->ContentRect().size(),
      1 / dest_to_content_scale_,
      1 / dest_to_content_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_data_.total_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::Rect
PictureLayerTiling::CoverageIterator::full_tile_geometry_rect() const {
  gfx::Rect rect = tiling_->tiling_data_.TileBoundsWithBorder(tile_i_, tile_j_);
  rect.set_size(tiling_->tiling_data_.max_texture_size());
  return 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.Offset(-tex_origin.OffsetFromOrigin());
  texture_rect.Intersect(tiling_->ContentRect());

  return texture_rect;
}

gfx::Size PictureLayerTiling::CoverageIterator::texture_size() const {
  return tiling_->tiling_data_.max_texture_size();
}

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

namespace {

bool NearlyOne(SkMScalar lhs) {
  return std::abs(lhs-1.0) < std::numeric_limits<float>::epsilon();
}

bool NearlyZero(SkMScalar lhs) {
  return std::abs(lhs) < std::numeric_limits<float>::epsilon();
}

bool ApproximatelyTranslation(const SkMatrix44& matrix) {
  return
      NearlyOne(matrix.get(0, 0)) &&
      NearlyZero(matrix.get(1, 0)) &&
      NearlyZero(matrix.get(2, 0)) &&
      matrix.get(3, 0) == 0 &&
      NearlyZero(matrix.get(0, 1)) &&
      NearlyOne(matrix.get(1, 1)) &&
      NearlyZero(matrix.get(2, 1)) &&
      matrix.get(3, 1) == 0 &&
      NearlyZero(matrix.get(0, 2)) &&
      NearlyZero(matrix.get(1, 2)) &&
      NearlyOne(matrix.get(2, 2)) &&
      matrix.get(3, 2) == 0 &&
      matrix.get(3, 3) == 1;
}

}  // namespace

void PictureLayerTiling::UpdateTilePriorities(
    WhichTree tree,
    gfx::Size device_viewport,
    gfx::Rect viewport_in_layer_space,
    gfx::Rect visible_layer_rect,
    gfx::Size last_layer_bounds,
    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) {
  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;
  }
  if (ContentRect().IsEmpty()) {
    last_impl_frame_time_in_seconds_ = current_frame_time_in_seconds;
    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_);

  gfx::Size tile_size = tiling_data_.max_texture_size();
  int64 interest_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());
  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 view_rect(device_viewport);
  float current_scale = current_layer_contents_scale / contents_scale_;
  float last_scale = last_layer_contents_scale / contents_scale_;

  bool store_screen_space_quads_on_tiles;
  TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                                     &store_screen_space_quads_on_tiles);

  // Fast path tile priority calculation when both transforms are translations.
  if (ApproximatelyTranslation(last_screen_transform.matrix()) &&
      ApproximatelyTranslation(current_screen_transform.matrix())) {
    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 =
          TilePriority::manhattanDistance(current_screen_rect, 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);
      if (store_screen_space_quads_on_tiles)
        priority.set_current_screen_quad(gfx::QuadF(current_screen_rect));
      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 =
          TilePriority::manhattanDistance(current_screen_rect, 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);

      if (store_screen_space_quads_on_tiles) {
        // This overhead is only triggered when logging event tracing data.
        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);
        bool clipped;
        priority.set_current_screen_quad(
            MathUtil::MapQuad(current_screen_transform,
                              gfx::QuadF(current_layer_content_rect),
                              &clipped));
      }
      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 =
          TilePriority::manhattanDistance(current_screen_rect, 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);
      if (store_screen_space_quads_on_tiles) {
        bool clipped;
        priority.set_current_screen_quad(
            MathUtil::MapQuad(current_screen_transform,
                              gfx::QuadF(current_layer_content_rect),
                              &clipped));
      }
      tile->SetPriority(tree, priority);
    }
  }

  last_impl_frame_time_in_seconds_ = current_frame_time_in_seconds;
}

void PictureLayerTiling::SetLiveTilesRect(
    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.
  for (TilingData::DifferenceIterator iter(&tiling_data_,
                                           live_tiles_rect_,
                                           new_live_tiles_rect);
       iter;
       ++iter) {
    TileMapKey key(iter.index());
    TileMap::iterator found = tiles_.find(key);
    // If the tile was outside of the recorded region, it won't exist even
    // though it was in the live rect.
    if (found != tiles_.end())
      tiles_.erase(found);
  }

  const PictureLayerTiling* twin_tiling = client_->GetTwinTiling(this);

  // 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());
    CreateTile(key.first, key.second, twin_tiling);
  }

  live_tiles_rect_ = new_live_tiles_rect;
}

void PictureLayerTiling::DidBecomeActive() {
  for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it) {
    it->second->SetPriority(ACTIVE_TREE, it->second->priority(PENDING_TREE));
    it->second->SetPriority(PENDING_TREE, TilePriority());

    // Tile holds a ref onto a picture pile. If the tile never gets invalidated
    // and recreated, then that picture pile ref could exist indefinitely.  To
    // prevent this, ask the client to update the pile to its own ref.  This
    // will cause PicturePileImpls and their clones to get deleted once the
    // corresponding PictureLayerImpl and any in flight raster jobs go out of
    // scope.
    client_->UpdatePile(it->second.get());
  }
}

void PictureLayerTiling::UpdateTilesToCurrentPile() {
  for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it) {
    client_->UpdatePile(it->second.get());
  }
}

scoped_ptr<base::Value> PictureLayerTiling::AsValue() const {
  scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
  state->SetInteger("num_tiles", tiles_.size());
  state->SetDouble("content_scale", contents_scale_);
  state->Set("content_bounds",
             MathUtil::AsValue(ContentRect().size()).release());
  return state.PassAs<base::Value>();
}

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.get();
    amount += tile->GPUMemoryUsageInBytes();
  }
  return amount;
}

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.
  return a == 0 ? -c / b :
     (-b + static_cast<int>(
         std::sqrt(static_cast<int64>(b) * b - 4.0 * a * c))) / (2 * a);
}

}  // namespace

gfx::Rect PictureLayerTiling::ExpandRectEquallyToAreaBoundedBy(
    gfx::Rect starting_rect,
    int64 target_area,
    gfx::Rect bounding_rect) {
  if (starting_rect.IsEmpty())
    return starting_rect;

  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.
    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.
    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;
  }

  return gfx::Rect(origin_x, origin_y, width, height);
}

}  // namespace cc