Source/WebCore/platform/graphics/TiledBackingStore.cpp - WebKit - Git at Google

 /*
  Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Library General Public
  License as published by the Free Software Foundation; either
  version 2 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Library General Public License for more details.

  You should have received a copy of the GNU Library General Public License
  along with this library; see the file COPYING.LIB.  If not, write to
  the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  Boston, MA 02110-1301, USA.
  */

 #include "config.h"
 #include "TiledBackingStore.h"

 #if USE(TILED_BACKING_STORE)

 #include "GraphicsContext.h"
 #include "TiledBackingStoreClient.h"

 namespace WebCore {

 static const int defaultTileWidth = 512;
 static const int defaultTileHeight = 512;

 static IntPoint innerBottomRight(const IntRect& rect)
 {
     // Actually, the rect does not contain rect.maxX(). Refer to IntRect::contain.
     return IntPoint(rect.maxX() - 1, rect.maxY() - 1);
 }

 TiledBackingStore::TiledBackingStore(TiledBackingStoreClient* client, PassOwnPtr<TiledBackingStoreBackend> backend)
     : m_client(client)
     , m_backend(backend)
     , m_tileBufferUpdateTimer(new TileTimer(this, &TiledBackingStore::tileBufferUpdateTimerFired))
     , m_tileCreationTimer(new TileTimer(this, &TiledBackingStore::tileCreationTimerFired))
     , m_tileSize(defaultTileWidth, defaultTileHeight)
     , m_tileCreationDelay(0.01)
     , m_keepAreaMultiplier(3.5f)
     , m_coverAreaMultiplier(2.5f)
     , m_contentsScale(1.f)
     , m_pendingScale(0)
     , m_contentsFrozen(false)
 {
     ASSERT(m_coverAreaMultiplier <= m_keepAreaMultiplier);
 }

 TiledBackingStore::~TiledBackingStore()
 {
     delete m_tileBufferUpdateTimer;
     delete m_tileCreationTimer;
 }

 void TiledBackingStore::setTileSize(const IntSize& size)
 {
     m_tileSize = size;
     m_tiles.clear();
     startTileCreationTimer();
 }

 void TiledBackingStore::setTileCreationDelay(double delay)
 {
     m_tileCreationDelay = delay;
 }

 void TiledBackingStore::setKeepAndCoverAreaMultipliers(float keepMultiplier, float coverMultiplier)
 {
     ASSERT(coverMultiplier <= keepMultiplier);
     m_keepAreaMultiplier = keepMultiplier;
     m_coverAreaMultiplier = coverMultiplier;
     startTileCreationTimer();
 }

 void TiledBackingStore::setVisibleRectTrajectoryVector(const FloatPoint& vector)
 {
     if (m_visibleRectTrajectoryVector == vector)
         return;

     m_visibleRectTrajectoryVector = vector;
     startTileCreationTimer();
 }

 void TiledBackingStore::invalidate(const IntRect& contentsDirtyRect)
 {
     IntRect dirtyRect(mapFromContents(contentsDirtyRect));

     Tile::Coordinate topLeft = tileCoordinateForPoint(dirtyRect.location());
     Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(dirtyRect));

     for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
         for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
             RefPtr<Tile> currentTile = tileAt(Tile::Coordinate(xCoordinate, yCoordinate));
             if (!currentTile)
                 continue;
             currentTile->invalidate(dirtyRect);
         }
     }

     startTileBufferUpdateTimer();
 }

 void TiledBackingStore::updateTileBuffers()
 {
     if (!m_client->tiledBackingStoreUpdatesAllowed() || m_contentsFrozen)
         return;

     m_client->tiledBackingStorePaintBegin();

     Vector<IntRect> paintedArea;
     Vector<RefPtr<Tile> > dirtyTiles;
     TileMap::iterator end = m_tiles.end();
     for (TileMap::iterator it = m_tiles.begin(); it != end; ++it) {
         if (!it->second->isDirty())
             continue;
         dirtyTiles.append(it->second);
     }

     if (dirtyTiles.isEmpty()) {
         m_client->tiledBackingStorePaintEnd(paintedArea);
         return;
     }

     // FIXME: In single threaded case, tile back buffers could be updated asynchronously
     // one by one and then swapped to front in one go. This would minimize the time spent
     // blocking on tile updates.
     unsigned size = dirtyTiles.size();
     for (unsigned n = 0; n < size; ++n) {
         Vector<IntRect> paintedRects = dirtyTiles[n]->updateBackBuffer();
         paintedArea.append(paintedRects);
         dirtyTiles[n]->swapBackBufferToFront();
     }

     m_client->tiledBackingStorePaintEnd(paintedArea);
 }

 void TiledBackingStore::paint(GraphicsContext* context, const IntRect& rect)
 {
     context->save();

     // Assumes the backing store is painted with the scale transform applied.
     // Since tile content is already scaled, first revert the scaling from the painter.
     context->scale(FloatSize(1.f / m_contentsScale, 1.f / m_contentsScale));

     IntRect dirtyRect = mapFromContents(rect);

     Tile::Coordinate topLeft = tileCoordinateForPoint(dirtyRect.location());
     Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(dirtyRect));

     for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
         for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
             Tile::Coordinate currentCoordinate(xCoordinate, yCoordinate);
             RefPtr<Tile> currentTile = tileAt(currentCoordinate);
             if (currentTile && currentTile->isReadyToPaint())
                 currentTile->paint(context, dirtyRect);
             else {
                 IntRect tileRect = tileRectForCoordinate(currentCoordinate);
                 IntRect target = intersection(tileRect, dirtyRect);
                 if (target.isEmpty())
                     continue;
                 m_backend->paintCheckerPattern(context, FloatRect(target));
             }
         }
     }
     context->restore();
 }

 void TiledBackingStore::adjustVisibleRect()
 {
     IntRect visibleRect = visibleContentsRect();
     if (m_previousVisibleRect == visibleRect)
         return;
     m_previousVisibleRect = visibleRect;

     startTileCreationTimer();
 }

 IntRect TiledBackingStore::visibleContentsRect()
 {
     return mapFromContents(intersection(m_client->tiledBackingStoreVisibleRect(), m_client->tiledBackingStoreContentsRect()));
 }

 void TiledBackingStore::setContentsScale(float scale)
 {
     if (m_pendingScale == m_contentsScale) {
         m_pendingScale = 0;
         return;
     }
     m_pendingScale = scale;
     if (m_contentsFrozen)
         return;
     commitScaleChange();
 }

 void TiledBackingStore::commitScaleChange()
 {
     m_contentsScale = m_pendingScale;
     m_pendingScale = 0;
     m_tiles.clear();
     createTiles();
 }

 double TiledBackingStore::tileDistance(const IntRect& viewport, const Tile::Coordinate& tileCoordinate) const
 {
     if (viewport.intersects(tileRectForCoordinate(tileCoordinate)))
         return 0;

     IntPoint viewCenter = viewport.location() + IntSize(viewport.width() / 2, viewport.height() / 2);
     Tile::Coordinate centerCoordinate = tileCoordinateForPoint(viewCenter);

     // Manhattan distance, biased so that vertical distances are shorter.
     const double horizontalBias = 1.3;
     return abs(centerCoordinate.y() - tileCoordinate.y()) + horizontalBias * abs(centerCoordinate.x() - tileCoordinate.x());
 }

 // Returns a ratio between 0.0f and 1.0f of the surface of contentsRect covered by rendered tiles.
 float TiledBackingStore::coverageRatio(const WebCore::IntRect& contentsRect)
 {
     IntRect dirtyRect = mapFromContents(contentsRect);
     float rectArea = dirtyRect.width() * dirtyRect.height();
     float coverArea = 0.0f;

     Tile::Coordinate topLeft = tileCoordinateForPoint(dirtyRect.location());
     Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(dirtyRect));

     for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
         for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
             Tile::Coordinate currentCoordinate(xCoordinate, yCoordinate);
             RefPtr<Tile> currentTile = tileAt(Tile::Coordinate(xCoordinate, yCoordinate));
             if (currentTile && currentTile->isReadyToPaint()) {
                 IntRect coverRect = intersection(dirtyRect, currentTile->rect());
                 coverArea += coverRect.width() * coverRect.height();
             }
         }
     }
     return coverArea / rectArea;
 }

 void TiledBackingStore::createTiles()
 {
     if (m_contentsFrozen)
         return;

     IntRect visibleRect = visibleContentsRect();
     m_previousVisibleRect = visibleRect;

     if (visibleRect.isEmpty())
         return;

     // Resize tiles on edges in case the contents size has changed.
     bool didResizeTiles = resizeEdgeTiles();

     IntRect keepRect = computeKeepRect(visibleRect);

     dropTilesOutsideRect(keepRect);

     IntRect coverRect = computeCoverRect(visibleRect);
     ASSERT(keepRect.contains(coverRect));

     // Search for the tile position closest to the viewport center that does not yet contain a tile.
     // Which position is considered the closest depends on the tileDistance function.
     double shortestDistance = std::numeric_limits<double>::infinity();
     Vector<Tile::Coordinate> tilesToCreate;
     unsigned requiredTileCount = 0;
     Tile::Coordinate topLeft = tileCoordinateForPoint(coverRect.location());
     Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(coverRect));
     for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
         for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
             Tile::Coordinate currentCoordinate(xCoordinate, yCoordinate);
             if (tileAt(currentCoordinate))
                 continue;
             ++requiredTileCount;
             // Distance is 0 for all currently visible tiles.
             double distance = tileDistance(visibleRect, currentCoordinate);
             if (distance > shortestDistance)
                 continue;
             if (distance < shortestDistance) {
                 tilesToCreate.clear();
                 shortestDistance = distance;
             }
             tilesToCreate.append(currentCoordinate);
         }
     }

     // Now construct the tile(s)
     unsigned tilesToCreateCount = tilesToCreate.size();
     for (unsigned n = 0; n < tilesToCreateCount; ++n) {
         Tile::Coordinate coordinate = tilesToCreate[n];
         setTile(coordinate, m_backend->createTile(this, coordinate));
     }
     requiredTileCount -= tilesToCreateCount;

     // Paint the content of the newly created tiles
     if (tilesToCreateCount || didResizeTiles)
         updateTileBuffers();

     // Keep creating tiles until the whole coverRect is covered.
     if (requiredTileCount)
         m_tileCreationTimer->startOneShot(m_tileCreationDelay);
 }

 IntRect TiledBackingStore::computeKeepRect(const IntRect& visibleRect) const
 {
     IntRect result = visibleRect;
     // Inflates to both sides, so divide the inflate delta by 2.
     result.inflateX(visibleRect.width() * (m_keepAreaMultiplier - 1) / 2);
     result.inflateY(visibleRect.height() * (m_keepAreaMultiplier - 1) / 2);
     result.intersect(contentsRect());

     return result;
 }

 // A null trajectory vector means that tiles intersecting all the coverArea (i.e. visibleRect * coverMultiplier) will be created.
 // A non-null trajectory vector will shrink the intersection rect to visibleRect plus its expansion from its
 // center toward the cover area edges in the direction of the given vector.
 // E.g. if visibleRect == (10,10)5x5 and coverMultiplier == 3.0:
 // a (0,0) trajectory vector will create tiles intersecting (5,5)15x15,
 // a (1,0) trajectory vector will create tiles intersecting (10,10)10x5,
 // and a (1,1) trajectory vector will create tiles intersecting (10,10)10x10.
 IntRect TiledBackingStore::computeCoverRect(const IntRect& visibleRect) const
 {
     IntRect result = visibleRect;
     float trajectoryVectorNorm = sqrt(pow(m_visibleRectTrajectoryVector.x(), 2) + pow(m_visibleRectTrajectoryVector.y(), 2));
     if (trajectoryVectorNorm > 0) {
         // Multiply the vector by the distance to the edge of the cover area.
         float trajectoryVectorMultiplier = (m_coverAreaMultiplier - 1) / 2;
         // Unite the visible rect with a "ghost" of the visible rect moved in the direction of the trajectory vector.
         result.move(result.width() * m_visibleRectTrajectoryVector.x() / trajectoryVectorNorm * trajectoryVectorMultiplier,
                     result.height() * m_visibleRectTrajectoryVector.y() / trajectoryVectorNorm * trajectoryVectorMultiplier);
         result.unite(visibleRect);
     } else {
         result.inflateX(visibleRect.width() * (m_coverAreaMultiplier - 1) / 2);
         result.inflateY(visibleRect.height() * (m_coverAreaMultiplier - 1) / 2);
     }
     result.intersect(contentsRect());

     return result;
 }

 bool TiledBackingStore::resizeEdgeTiles()
 {
     bool wasResized = false;

     Vector<Tile::Coordinate> tilesToRemove;
     TileMap::iterator end = m_tiles.end();
     for (TileMap::iterator it = m_tiles.begin(); it != end; ++it) {
         Tile::Coordinate tileCoordinate = it->second->coordinate();
         IntRect tileRect = it->second->rect();
         IntRect expectedTileRect = tileRectForCoordinate(tileCoordinate);
         if (expectedTileRect.isEmpty())
             tilesToRemove.append(tileCoordinate);
         else if (expectedTileRect != tileRect) {
             it->second->resize(expectedTileRect.size());
             wasResized = true;
         }
     }
     unsigned removeCount = tilesToRemove.size();
     for (unsigned n = 0; n < removeCount; ++n)
         removeTile(tilesToRemove[n]);
     return wasResized;
 }

 void TiledBackingStore::dropTilesOutsideRect(const IntRect& keepRect)
 {
     FloatRect keepRectF = keepRect;

     Vector<Tile::Coordinate> toRemove;
     TileMap::iterator end = m_tiles.end();
     for (TileMap::iterator it = m_tiles.begin(); it != end; ++it) {
         Tile::Coordinate coordinate = it->second->coordinate();
         FloatRect tileRect = it->second->rect();
         if (!tileRect.intersects(keepRectF))
             toRemove.append(coordinate);
     }
     unsigned removeCount = toRemove.size();
     for (unsigned n = 0; n < removeCount; ++n)
         removeTile(toRemove[n]);
 }

 PassRefPtr<Tile> TiledBackingStore::tileAt(const Tile::Coordinate& coordinate) const
 {
     return m_tiles.get(coordinate);
 }

 void TiledBackingStore::setTile(const Tile::Coordinate& coordinate, PassRefPtr<Tile> tile)
 {
     m_tiles.set(coordinate, tile);
 }

 void TiledBackingStore::removeTile(const Tile::Coordinate& coordinate)
 {
     m_tiles.remove(coordinate);
 }

 IntRect TiledBackingStore::mapToContents(const IntRect& rect) const
 {
     return enclosingIntRect(FloatRect(rect.x() / m_contentsScale,
         rect.y() / m_contentsScale,
         rect.width() / m_contentsScale,
         rect.height() / m_contentsScale));
 }

 IntRect TiledBackingStore::mapFromContents(const IntRect& rect) const
 {
     return enclosingIntRect(FloatRect(rect.x() * m_contentsScale,
         rect.y() * m_contentsScale,
         rect.width() * m_contentsScale,
         rect.height() * m_contentsScale));
 }

 IntRect TiledBackingStore::contentsRect() const
 {
     return mapFromContents(m_client->tiledBackingStoreContentsRect());
 }

 IntRect TiledBackingStore::tileRectForCoordinate(const Tile::Coordinate& coordinate) const
 {
     IntRect rect(coordinate.x() * m_tileSize.width(),
         coordinate.y() * m_tileSize.height(),
         m_tileSize.width(),
         m_tileSize.height());

     rect.intersect(contentsRect());
     return rect;
 }

 Tile::Coordinate TiledBackingStore::tileCoordinateForPoint(const IntPoint& point) const
 {
     int x = point.x() / m_tileSize.width();
     int y = point.y() / m_tileSize.height();
     return Tile::Coordinate(std::max(x, 0), std::max(y, 0));
 }


 void TiledBackingStore::startTileBufferUpdateTimer()
 {
     if (m_tileBufferUpdateTimer->isActive() || !m_client->tiledBackingStoreUpdatesAllowed() || m_contentsFrozen)
         return;
     m_tileBufferUpdateTimer->startOneShot(0);
 }

 void TiledBackingStore::tileBufferUpdateTimerFired(TileTimer*)
 {
     updateTileBuffers();
 }

 void TiledBackingStore::startTileCreationTimer()
 {
     if (m_tileCreationTimer->isActive() || m_contentsFrozen)
         return;
     m_tileCreationTimer->startOneShot(0);
 }

 void TiledBackingStore::tileCreationTimerFired(TileTimer*)
 {
     createTiles();
 }

 void TiledBackingStore::setContentsFrozen(bool freeze)
 {
     if (m_contentsFrozen == freeze)
         return;

     m_contentsFrozen = freeze;

     // Restart the timers. There might be pending invalidations that
     // were not painted or created because tiles are not created or
     // painted when in frozen state.
     if (m_contentsFrozen)
         return;
     if (m_pendingScale)
         commitScaleChange();
     else {
         startTileCreationTimer();
         startTileBufferUpdateTimer();
     }
 }

 }

 #endif
	/*
	Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)

	This library is free software; you can redistribute it and/or
	modify it under the terms of the GNU Library General Public
	License as published by the Free Software Foundation; either
	version 2 of the License, or (at your option) any later version.

	This library is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	Library General Public License for more details.

	You should have received a copy of the GNU Library General Public License
	along with this library; see the file COPYING.LIB. If not, write to
	the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
	Boston, MA 02110-1301, USA.
	*/

	#include "config.h"
	#include "TiledBackingStore.h"

	#if USE(TILED_BACKING_STORE)

	#include "GraphicsContext.h"
	#include "TiledBackingStoreClient.h"

	namespace WebCore {

	static const int defaultTileWidth = 512;
	static const int defaultTileHeight = 512;

	static IntPoint innerBottomRight(const IntRect& rect)
	{
	// Actually, the rect does not contain rect.maxX(). Refer to IntRect::contain.
	return IntPoint(rect.maxX() - 1, rect.maxY() - 1);
	}

	TiledBackingStore::TiledBackingStore(TiledBackingStoreClient* client, PassOwnPtr<TiledBackingStoreBackend> backend)
	: m_client(client)
	, m_backend(backend)
	, m_tileBufferUpdateTimer(new TileTimer(this, &TiledBackingStore::tileBufferUpdateTimerFired))
	, m_tileCreationTimer(new TileTimer(this, &TiledBackingStore::tileCreationTimerFired))
	, m_tileSize(defaultTileWidth, defaultTileHeight)
	, m_tileCreationDelay(0.01)
	, m_keepAreaMultiplier(3.5f)
	, m_coverAreaMultiplier(2.5f)
	, m_contentsScale(1.f)
	, m_pendingScale(0)
	, m_contentsFrozen(false)
	{
	ASSERT(m_coverAreaMultiplier <= m_keepAreaMultiplier);
	}

	TiledBackingStore::~TiledBackingStore()
	{
	delete m_tileBufferUpdateTimer;
	delete m_tileCreationTimer;
	}

	void TiledBackingStore::setTileSize(const IntSize& size)
	{
	m_tileSize = size;
	m_tiles.clear();
	startTileCreationTimer();
	}

	void TiledBackingStore::setTileCreationDelay(double delay)
	{
	m_tileCreationDelay = delay;
	}

	void TiledBackingStore::setKeepAndCoverAreaMultipliers(float keepMultiplier, float coverMultiplier)
	{
	ASSERT(coverMultiplier <= keepMultiplier);
	m_keepAreaMultiplier = keepMultiplier;
	m_coverAreaMultiplier = coverMultiplier;
	startTileCreationTimer();
	}

	void TiledBackingStore::setVisibleRectTrajectoryVector(const FloatPoint& vector)
	{
	if (m_visibleRectTrajectoryVector == vector)
	return;

	m_visibleRectTrajectoryVector = vector;
	startTileCreationTimer();
	}

	void TiledBackingStore::invalidate(const IntRect& contentsDirtyRect)
	{
	IntRect dirtyRect(mapFromContents(contentsDirtyRect));

	Tile::Coordinate topLeft = tileCoordinateForPoint(dirtyRect.location());
	Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(dirtyRect));

	for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
	for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
	RefPtr<Tile> currentTile = tileAt(Tile::Coordinate(xCoordinate, yCoordinate));
	if (!currentTile)
	continue;
	currentTile->invalidate(dirtyRect);
	}
	}

	startTileBufferUpdateTimer();
	}

	void TiledBackingStore::updateTileBuffers()
	{
	if (!m_client->tiledBackingStoreUpdatesAllowed() \|\| m_contentsFrozen)
	return;

	m_client->tiledBackingStorePaintBegin();

	Vector<IntRect> paintedArea;
	Vector<RefPtr<Tile> > dirtyTiles;
	TileMap::iterator end = m_tiles.end();
	for (TileMap::iterator it = m_tiles.begin(); it != end; ++it) {
	if (!it->second->isDirty())
	continue;
	dirtyTiles.append(it->second);
	}

	if (dirtyTiles.isEmpty()) {
	m_client->tiledBackingStorePaintEnd(paintedArea);
	return;
	}

	// FIXME: In single threaded case, tile back buffers could be updated asynchronously
	// one by one and then swapped to front in one go. This would minimize the time spent
	// blocking on tile updates.
	unsigned size = dirtyTiles.size();
	for (unsigned n = 0; n < size; ++n) {
	Vector<IntRect> paintedRects = dirtyTiles[n]->updateBackBuffer();
	paintedArea.append(paintedRects);
	dirtyTiles[n]->swapBackBufferToFront();
	}

	m_client->tiledBackingStorePaintEnd(paintedArea);
	}

	void TiledBackingStore::paint(GraphicsContext* context, const IntRect& rect)
	{
	context->save();

	// Assumes the backing store is painted with the scale transform applied.
	// Since tile content is already scaled, first revert the scaling from the painter.
	context->scale(FloatSize(1.f / m_contentsScale, 1.f / m_contentsScale));

	IntRect dirtyRect = mapFromContents(rect);

	Tile::Coordinate topLeft = tileCoordinateForPoint(dirtyRect.location());
	Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(dirtyRect));

	for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
	for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
	Tile::Coordinate currentCoordinate(xCoordinate, yCoordinate);
	RefPtr<Tile> currentTile = tileAt(currentCoordinate);
	if (currentTile && currentTile->isReadyToPaint())
	currentTile->paint(context, dirtyRect);
	else {
	IntRect tileRect = tileRectForCoordinate(currentCoordinate);
	IntRect target = intersection(tileRect, dirtyRect);
	if (target.isEmpty())
	continue;
	m_backend->paintCheckerPattern(context, FloatRect(target));
	}
	}
	}
	context->restore();
	}

	void TiledBackingStore::adjustVisibleRect()
	{
	IntRect visibleRect = visibleContentsRect();
	if (m_previousVisibleRect == visibleRect)
	return;
	m_previousVisibleRect = visibleRect;

	startTileCreationTimer();
	}

	IntRect TiledBackingStore::visibleContentsRect()
	{
	return mapFromContents(intersection(m_client->tiledBackingStoreVisibleRect(), m_client->tiledBackingStoreContentsRect()));
	}

	void TiledBackingStore::setContentsScale(float scale)
	{
	if (m_pendingScale == m_contentsScale) {
	m_pendingScale = 0;
	return;
	}
	m_pendingScale = scale;
	if (m_contentsFrozen)
	return;
	commitScaleChange();
	}

	void TiledBackingStore::commitScaleChange()
	{
	m_contentsScale = m_pendingScale;
	m_pendingScale = 0;
	m_tiles.clear();
	createTiles();
	}

	double TiledBackingStore::tileDistance(const IntRect& viewport, const Tile::Coordinate& tileCoordinate) const
	{
	if (viewport.intersects(tileRectForCoordinate(tileCoordinate)))
	return 0;

	IntPoint viewCenter = viewport.location() + IntSize(viewport.width() / 2, viewport.height() / 2);
	Tile::Coordinate centerCoordinate = tileCoordinateForPoint(viewCenter);

	// Manhattan distance, biased so that vertical distances are shorter.
	const double horizontalBias = 1.3;
	return abs(centerCoordinate.y() - tileCoordinate.y()) + horizontalBias * abs(centerCoordinate.x() - tileCoordinate.x());
	}

	// Returns a ratio between 0.0f and 1.0f of the surface of contentsRect covered by rendered tiles.
	float TiledBackingStore::coverageRatio(const WebCore::IntRect& contentsRect)
	{
	IntRect dirtyRect = mapFromContents(contentsRect);
	float rectArea = dirtyRect.width() * dirtyRect.height();
	float coverArea = 0.0f;

	Tile::Coordinate topLeft = tileCoordinateForPoint(dirtyRect.location());
	Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(dirtyRect));

	for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
	for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
	Tile::Coordinate currentCoordinate(xCoordinate, yCoordinate);
	RefPtr<Tile> currentTile = tileAt(Tile::Coordinate(xCoordinate, yCoordinate));
	if (currentTile && currentTile->isReadyToPaint()) {
	IntRect coverRect = intersection(dirtyRect, currentTile->rect());
	coverArea += coverRect.width() * coverRect.height();
	}
	}
	}
	return coverArea / rectArea;
	}

	void TiledBackingStore::createTiles()
	{
	if (m_contentsFrozen)
	return;

	IntRect visibleRect = visibleContentsRect();
	m_previousVisibleRect = visibleRect;

	if (visibleRect.isEmpty())
	return;

	// Resize tiles on edges in case the contents size has changed.
	bool didResizeTiles = resizeEdgeTiles();

	IntRect keepRect = computeKeepRect(visibleRect);

	dropTilesOutsideRect(keepRect);

	IntRect coverRect = computeCoverRect(visibleRect);
	ASSERT(keepRect.contains(coverRect));

	// Search for the tile position closest to the viewport center that does not yet contain a tile.
	// Which position is considered the closest depends on the tileDistance function.
	double shortestDistance = std::numeric_limits<double>::infinity();
	Vector<Tile::Coordinate> tilesToCreate;
	unsigned requiredTileCount = 0;
	Tile::Coordinate topLeft = tileCoordinateForPoint(coverRect.location());
	Tile::Coordinate bottomRight = tileCoordinateForPoint(innerBottomRight(coverRect));
	for (unsigned yCoordinate = topLeft.y(); yCoordinate <= bottomRight.y(); ++yCoordinate) {
	for (unsigned xCoordinate = topLeft.x(); xCoordinate <= bottomRight.x(); ++xCoordinate) {
	Tile::Coordinate currentCoordinate(xCoordinate, yCoordinate);
	if (tileAt(currentCoordinate))
	continue;
	++requiredTileCount;
	// Distance is 0 for all currently visible tiles.
	double distance = tileDistance(visibleRect, currentCoordinate);
	if (distance > shortestDistance)
	continue;
	if (distance < shortestDistance) {
	tilesToCreate.clear();
	shortestDistance = distance;
	}
	tilesToCreate.append(currentCoordinate);
	}
	}

	// Now construct the tile(s)
	unsigned tilesToCreateCount = tilesToCreate.size();
	for (unsigned n = 0; n < tilesToCreateCount; ++n) {
	Tile::Coordinate coordinate = tilesToCreate[n];
	setTile(coordinate, m_backend->createTile(this, coordinate));
	}
	requiredTileCount -= tilesToCreateCount;

	// Paint the content of the newly created tiles
	if (tilesToCreateCount \|\| didResizeTiles)
	updateTileBuffers();

	// Keep creating tiles until the whole coverRect is covered.
	if (requiredTileCount)
	m_tileCreationTimer->startOneShot(m_tileCreationDelay);
	}

	IntRect TiledBackingStore::computeKeepRect(const IntRect& visibleRect) const
	{
	IntRect result = visibleRect;
	// Inflates to both sides, so divide the inflate delta by 2.
	result.inflateX(visibleRect.width() * (m_keepAreaMultiplier - 1) / 2);
	result.inflateY(visibleRect.height() * (m_keepAreaMultiplier - 1) / 2);
	result.intersect(contentsRect());

	return result;
	}

	// A null trajectory vector means that tiles intersecting all the coverArea (i.e. visibleRect * coverMultiplier) will be created.
	// A non-null trajectory vector will shrink the intersection rect to visibleRect plus its expansion from its
	// center toward the cover area edges in the direction of the given vector.
	// E.g. if visibleRect == (10,10)5x5 and coverMultiplier == 3.0:
	// a (0,0) trajectory vector will create tiles intersecting (5,5)15x15,
	// a (1,0) trajectory vector will create tiles intersecting (10,10)10x5,
	// and a (1,1) trajectory vector will create tiles intersecting (10,10)10x10.
	IntRect TiledBackingStore::computeCoverRect(const IntRect& visibleRect) const
	{
	IntRect result = visibleRect;
	float trajectoryVectorNorm = sqrt(pow(m_visibleRectTrajectoryVector.x(), 2) + pow(m_visibleRectTrajectoryVector.y(), 2));
	if (trajectoryVectorNorm > 0) {
	// Multiply the vector by the distance to the edge of the cover area.
	float trajectoryVectorMultiplier = (m_coverAreaMultiplier - 1) / 2;
	// Unite the visible rect with a "ghost" of the visible rect moved in the direction of the trajectory vector.
	result.move(result.width() * m_visibleRectTrajectoryVector.x() / trajectoryVectorNorm * trajectoryVectorMultiplier,
	result.height() * m_visibleRectTrajectoryVector.y() / trajectoryVectorNorm * trajectoryVectorMultiplier);
	result.unite(visibleRect);
	} else {
	result.inflateX(visibleRect.width() * (m_coverAreaMultiplier - 1) / 2);
	result.inflateY(visibleRect.height() * (m_coverAreaMultiplier - 1) / 2);
	}
	result.intersect(contentsRect());

	return result;
	}

	bool TiledBackingStore::resizeEdgeTiles()
	{
	bool wasResized = false;

	Vector<Tile::Coordinate> tilesToRemove;
	TileMap::iterator end = m_tiles.end();
	for (TileMap::iterator it = m_tiles.begin(); it != end; ++it) {
	Tile::Coordinate tileCoordinate = it->second->coordinate();
	IntRect tileRect = it->second->rect();
	IntRect expectedTileRect = tileRectForCoordinate(tileCoordinate);
	if (expectedTileRect.isEmpty())
	tilesToRemove.append(tileCoordinate);
	else if (expectedTileRect != tileRect) {
	it->second->resize(expectedTileRect.size());
	wasResized = true;
	}
	}
	unsigned removeCount = tilesToRemove.size();
	for (unsigned n = 0; n < removeCount; ++n)
	removeTile(tilesToRemove[n]);
	return wasResized;
	}

	void TiledBackingStore::dropTilesOutsideRect(const IntRect& keepRect)
	{
	FloatRect keepRectF = keepRect;

	Vector<Tile::Coordinate> toRemove;
	TileMap::iterator end = m_tiles.end();
	for (TileMap::iterator it = m_tiles.begin(); it != end; ++it) {
	Tile::Coordinate coordinate = it->second->coordinate();
	FloatRect tileRect = it->second->rect();
	if (!tileRect.intersects(keepRectF))
	toRemove.append(coordinate);
	}
	unsigned removeCount = toRemove.size();
	for (unsigned n = 0; n < removeCount; ++n)
	removeTile(toRemove[n]);
	}

	PassRefPtr<Tile> TiledBackingStore::tileAt(const Tile::Coordinate& coordinate) const
	{
	return m_tiles.get(coordinate);
	}

	void TiledBackingStore::setTile(const Tile::Coordinate& coordinate, PassRefPtr<Tile> tile)
	{
	m_tiles.set(coordinate, tile);
	}

	void TiledBackingStore::removeTile(const Tile::Coordinate& coordinate)
	{
	m_tiles.remove(coordinate);
	}

	IntRect TiledBackingStore::mapToContents(const IntRect& rect) const
	{
	return enclosingIntRect(FloatRect(rect.x() / m_contentsScale,
	rect.y() / m_contentsScale,
	rect.width() / m_contentsScale,
	rect.height() / m_contentsScale));
	}

	IntRect TiledBackingStore::mapFromContents(const IntRect& rect) const
	{
	return enclosingIntRect(FloatRect(rect.x() * m_contentsScale,
	rect.y() * m_contentsScale,
	rect.width() * m_contentsScale,
	rect.height() * m_contentsScale));
	}

	IntRect TiledBackingStore::contentsRect() const
	{
	return mapFromContents(m_client->tiledBackingStoreContentsRect());
	}

	IntRect TiledBackingStore::tileRectForCoordinate(const Tile::Coordinate& coordinate) const
	{
	IntRect rect(coordinate.x() * m_tileSize.width(),
	coordinate.y() * m_tileSize.height(),
	m_tileSize.width(),
	m_tileSize.height());

	rect.intersect(contentsRect());
	return rect;
	}

	Tile::Coordinate TiledBackingStore::tileCoordinateForPoint(const IntPoint& point) const
	{
	int x = point.x() / m_tileSize.width();
	int y = point.y() / m_tileSize.height();
	return Tile::Coordinate(std::max(x, 0), std::max(y, 0));
	}


	void TiledBackingStore::startTileBufferUpdateTimer()
	{
	if (m_tileBufferUpdateTimer->isActive() \|\| !m_client->tiledBackingStoreUpdatesAllowed() \|\| m_contentsFrozen)
	return;
	m_tileBufferUpdateTimer->startOneShot(0);
	}

	void TiledBackingStore::tileBufferUpdateTimerFired(TileTimer*)
	{
	updateTileBuffers();
	}

	void TiledBackingStore::startTileCreationTimer()
	{
	if (m_tileCreationTimer->isActive() \|\| m_contentsFrozen)
	return;
	m_tileCreationTimer->startOneShot(0);
	}

	void TiledBackingStore::tileCreationTimerFired(TileTimer*)
	{
	createTiles();
	}

	void TiledBackingStore::setContentsFrozen(bool freeze)
	{
	if (m_contentsFrozen == freeze)
	return;

	m_contentsFrozen = freeze;

	// Restart the timers. There might be pending invalidations that
	// were not painted or created because tiles are not created or
	// painted when in frozen state.
	if (m_contentsFrozen)
	return;
	if (m_pendingScale)
	commitScaleChange();
	else {
	startTileCreationTimer();
	startTileBufferUpdateTimer();
	}
	}

	}

	#endif