Initial import attempt, just to play with. Many things disabled/removed

ui/cc/TiledLayerChromium.cpp

Index: ui/cc/TiledLayerChromium.cpp
diff --git a/ui/cc/TiledLayerChromium.cpp b/ui/cc/TiledLayerChromium.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..f02a378a0fd659e712dd66084e32d6b98d8d1e9b
--- /dev/null
+++ b/ui/cc/TiledLayerChromium.cpp
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+/*
+ * Copyright (C) 2011 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+
+#if USE(ACCELERATED_COMPOSITING)
+
+#include "TiledLayerChromium.h"
+
+#include "GraphicsContext3D.h"
+#include "ManagedTexture.h"
+#include "Region.h"
+#include "TextStream.h"
+
+#include "cc/CCLayerImpl.h"
+#include "cc/CCLayerTreeHost.h"
+#include "cc/CCOverdrawMetrics.h"
+#include "cc/CCTextureUpdater.h"
+#include "cc/CCTiledLayerImpl.h"
+
+#include <wtf/CurrentTime.h>
+#include <wtf/MathExtras.h>
+
+using namespace std;
+using WebKit::WebTransformationMatrix;
+
+namespace WebCore {
+
+class UpdatableTile : public CCLayerTilingData::Tile {
+    WTF_MAKE_NONCOPYABLE(UpdatableTile);
+public:
+    static PassOwnPtr<UpdatableTile> create(PassOwnPtr<LayerTextureUpdater::Texture> texture)
+    {
+        return adoptPtr(new UpdatableTile(texture));
+    }
+
+    LayerTextureUpdater::Texture* texture() { return m_texture.get(); }
+    ManagedTexture* managedTexture() { return m_texture->texture(); }
+
+    bool isDirty() const { return !dirtyRect.isEmpty(); }
+    void copyAndClearDirty()
+    {
+        updateRect = dirtyRect;
+        dirtyRect = IntRect();
+    }
+    // Returns whether the layer was dirty and not updated in the current frame. For tiles that were not culled, the
+    // updateRect holds the area of the tile that was updated. Otherwise, the area that would have been updated.
+    bool isDirtyForCurrentFrame() { return !dirtyRect.isEmpty() && (updateRect.isEmpty() || !updated); }
+
+    IntRect dirtyRect;
+    IntRect updateRect;
+    bool partialUpdate;
+    bool updated;
+    bool isInUseOnImpl;
+private:
+    explicit UpdatableTile(PassOwnPtr<LayerTextureUpdater::Texture> texture)
+        : partialUpdate(false)
+        , updated(false)
+        , isInUseOnImpl(false)
+        , m_texture(texture)
+    {
+    }
+
+    OwnPtr<LayerTextureUpdater::Texture> m_texture;
+};
+
+TiledLayerChromium::TiledLayerChromium()
+    : LayerChromium()
+    , m_textureFormat(GL_INVALID_ENUM)
+    , m_skipsDraw(false)
+    , m_skipsIdlePaint(false)
+    , m_sampledTexelFormat(LayerTextureUpdater::SampledTexelFormatInvalid)
+    , m_didPaint(false)
+    , m_tilingOption(AutoTile)
+{
+    m_tiler = CCLayerTilingData::create(IntSize(), CCLayerTilingData::HasBorderTexels);
+}
+
+TiledLayerChromium::~TiledLayerChromium()
+{
+}
+
+PassOwnPtr<CCLayerImpl> TiledLayerChromium::createCCLayerImpl()
+{
+    return CCTiledLayerImpl::create(id());
+}
+
+void TiledLayerChromium::updateTileSizeAndTilingOption()
+{
+    ASSERT(layerTreeHost());
+
+    const IntSize& defaultTileSize = layerTreeHost()->settings().defaultTileSize;
+    const IntSize& maxUntiledLayerSize = layerTreeHost()->settings().maxUntiledLayerSize;
+    int layerWidth = contentBounds().width();
+    int layerHeight = contentBounds().height();
+
+    const IntSize tileSize(min(defaultTileSize.width(), layerWidth), min(defaultTileSize.height(), layerHeight));
+
+    // Tile if both dimensions large, or any one dimension large and the other
+    // extends into a second tile but the total layer area isn't larger than that
+    // of the largest possible untiled layer. This heuristic allows for long skinny layers
+    // (e.g. scrollbars) that are Nx1 tiles to minimize wasted texture space but still avoids
+    // creating very large tiles.
+    const bool anyDimensionLarge = layerWidth > maxUntiledLayerSize.width() || layerHeight > maxUntiledLayerSize.height();
+    const bool anyDimensionOneTile = (layerWidth <= defaultTileSize.width() || layerHeight <= defaultTileSize.height())
+                                      && (layerWidth * layerHeight) <= (maxUntiledLayerSize.width() * maxUntiledLayerSize.height());
+    const bool autoTiled = anyDimensionLarge && !anyDimensionOneTile;
+
+    bool isTiled;
+    if (m_tilingOption == AlwaysTile)
+        isTiled = true;
+    else if (m_tilingOption == NeverTile)
+        isTiled = false;
+    else
+        isTiled = autoTiled;
+
+    IntSize requestedSize = isTiled ? tileSize : contentBounds();
+    const int maxSize = layerTreeHost()->layerRendererCapabilities().maxTextureSize;
+    IntSize clampedSize = requestedSize.shrunkTo(IntSize(maxSize, maxSize));
+    setTileSize(clampedSize);
+}
+
+void TiledLayerChromium::updateBounds()
+{
+    IntSize oldBounds = m_tiler->bounds();
+    IntSize newBounds = contentBounds();
+    if (oldBounds == newBounds)
+        return;
+    m_tiler->setBounds(newBounds);
+
+    // Invalidate any areas that the new bounds exposes.
+    Region oldRegion(IntRect(IntPoint(), oldBounds));
+    Region newRegion(IntRect(IntPoint(), newBounds));
+    newRegion.subtract(oldRegion);
+    Vector<IntRect> rects = newRegion.rects();
+    for (size_t i = 0; i < rects.size(); ++i)
+        invalidateRect(rects[i]);
+}
+
+void TiledLayerChromium::setTileSize(const IntSize& size)
+{
+    m_tiler->setTileSize(size);
+}
+
+void TiledLayerChromium::setBorderTexelOption(CCLayerTilingData::BorderTexelOption borderTexelOption)
+{
+    m_tiler->setBorderTexelOption(borderTexelOption);
+}
+
+bool TiledLayerChromium::drawsContent() const
+{
+    if (!LayerChromium::drawsContent())
+        return false;
+
+    bool hasMoreThanOneTile = m_tiler->numTilesX() > 1 || m_tiler->numTilesY() > 1;
+    if (m_tilingOption == NeverTile && hasMoreThanOneTile)
+        return false;
+
+    return true;
+}
+
+bool TiledLayerChromium::needsContentsScale() const
+{
+    return true;
+}
+
+IntSize TiledLayerChromium::contentBounds() const
+{
+    return IntSize(lroundf(bounds().width() * contentsScale()), lroundf(bounds().height() * contentsScale()));
+}
+
+void TiledLayerChromium::setTilingOption(TilingOption tilingOption)
+{
+    m_tilingOption = tilingOption;
+}
+
+void TiledLayerChromium::setIsMask(bool isMask)
+{
+    setTilingOption(isMask ? NeverTile : AutoTile);
+}
+
+void TiledLayerChromium::pushPropertiesTo(CCLayerImpl* layer)
+{
+    LayerChromium::pushPropertiesTo(layer);
+
+    CCTiledLayerImpl* tiledLayer = static_cast<CCTiledLayerImpl*>(layer);
+
+    tiledLayer->setSkipsDraw(m_skipsDraw);
+    tiledLayer->setContentsSwizzled(m_sampledTexelFormat != LayerTextureUpdater::SampledTexelFormatRGBA);
+    tiledLayer->setTilingData(*m_tiler);
+    Vector<UpdatableTile*> invalidTiles;
+
+    for (CCLayerTilingData::TileMap::const_iterator iter = m_tiler->tiles().begin(); iter != m_tiler->tiles().end(); ++iter) {
+        int i = iter->first.first;
+        int j = iter->first.second;
+        UpdatableTile* tile = static_cast<UpdatableTile*>(iter->second.get());
+        // FIXME: This should not ever be null.
+        if (!tile)
+            continue;
+        tile->isInUseOnImpl = false;
+        if (!tile->managedTexture()->isValid(m_tiler->tileSize(), m_textureFormat)) {
+            invalidTiles.append(tile);
+            continue;
+        }
+        if (tile->isDirtyForCurrentFrame())
+            continue;
+
+        tiledLayer->pushTileProperties(i, j, tile->managedTexture()->textureId(), tile->opaqueRect());
+        tile->isInUseOnImpl = true;
+    }
+    for (Vector<UpdatableTile*>::const_iterator iter = invalidTiles.begin(); iter != invalidTiles.end(); ++iter)
+        m_tiler->takeTile((*iter)->i(), (*iter)->j());
+}
+
+TextureManager* TiledLayerChromium::textureManager() const
+{
+    if (!layerTreeHost())
+        return 0;
+    return layerTreeHost()->contentsTextureManager();
+}
+
+void TiledLayerChromium::setLayerTreeHost(CCLayerTreeHost* host)
+{
+    if (host && host != layerTreeHost()) {
+        for (CCLayerTilingData::TileMap::const_iterator iter = m_tiler->tiles().begin(); iter != m_tiler->tiles().end(); ++iter) {
+            UpdatableTile* tile = static_cast<UpdatableTile*>(iter->second.get());
+            // FIXME: This should not ever be null.
+            if (!tile)
+                continue;
+            tile->managedTexture()->setTextureManager(host->contentsTextureManager());
+        }
+    }
+    LayerChromium::setLayerTreeHost(host);
+}
+
+UpdatableTile* TiledLayerChromium::tileAt(int i, int j) const
+{
+    return static_cast<UpdatableTile*>(m_tiler->tileAt(i, j));
+}
+
+UpdatableTile* TiledLayerChromium::createTile(int i, int j)
+{
+    OwnPtr<UpdatableTile> tile(UpdatableTile::create(textureUpdater()->createTexture(textureManager())));
+    UpdatableTile* addedTile = tile.get();
+    m_tiler->addTile(tile.release(), i, j);
+
+    addedTile->dirtyRect = m_tiler->tileRect(addedTile);
+
+    // Temporary diagnostic crash.
+    if (!addedTile)
+        CRASH();
+    if (!tileAt(i, j))
+        CRASH();
+
+    return addedTile;
+}
+
+void TiledLayerChromium::setNeedsDisplayRect(const FloatRect& dirtyRect)
+{
+    FloatRect scaledDirtyRect(dirtyRect);
+    scaledDirtyRect.scale(contentsScale());
+    IntRect dirty = enclosingIntRect(scaledDirtyRect);
+    invalidateRect(dirty);
+    LayerChromium::setNeedsDisplayRect(dirtyRect);
+}
+
+void TiledLayerChromium::setIsNonCompositedContent(bool isNonCompositedContent)
+{
+    LayerChromium::setIsNonCompositedContent(isNonCompositedContent);
+
+    CCLayerTilingData::BorderTexelOption borderTexelOption;
+#if OS(ANDROID)
+    // Always want border texels and GL_LINEAR due to pinch zoom.
+    borderTexelOption = CCLayerTilingData::HasBorderTexels;
+#else
+    borderTexelOption = isNonCompositedContent ? CCLayerTilingData::NoBorderTexels : CCLayerTilingData::HasBorderTexels;
+#endif
+    setBorderTexelOption(borderTexelOption);
+}
+
+void TiledLayerChromium::invalidateRect(const IntRect& layerRect)
+{
+    updateBounds();
+    if (m_tiler->isEmpty() || layerRect.isEmpty() || m_skipsDraw)
+        return;
+
+    for (CCLayerTilingData::TileMap::const_iterator iter = m_tiler->tiles().begin(); iter != m_tiler->tiles().end(); ++iter) {
+        UpdatableTile* tile = static_cast<UpdatableTile*>(iter->second.get());
+        ASSERT(tile);
+        // FIXME: This should not ever be null.
+        if (!tile)
+            continue;
+        IntRect bound = m_tiler->tileRect(tile);
+        bound.intersect(layerRect);
+        tile->dirtyRect.unite(bound);
+    }
+}
+
+void TiledLayerChromium::protectTileTextures(const IntRect& layerRect)
+{
+    if (m_tiler->isEmpty() || layerRect.isEmpty())
+        return;
+
+    int left, top, right, bottom;
+    m_tiler->layerRectToTileIndices(layerRect, left, top, right, bottom);
+
+    for (int j = top; j <= bottom; ++j) {
+        for (int i = left; i <= right; ++i) {
+            UpdatableTile* tile = tileAt(i, j);
+            if (!tile || !tile->managedTexture()->isValid(m_tiler->tileSize(), m_textureFormat))
+                continue;
+
+            tile->managedTexture()->reserve(m_tiler->tileSize(), m_textureFormat);
+        }
+    }
+}
+
+// Returns true if tile is dirty and only part of it needs to be updated.
+bool TiledLayerChromium::tileOnlyNeedsPartialUpdate(UpdatableTile* tile)
+{
+    return !tile->dirtyRect.contains(m_tiler->tileRect(tile));
+}
+
+// Dirty tiles with valid textures needs buffered update to guarantee that
+// we don't modify textures currently used for drawing by the impl thread.
+bool TiledLayerChromium::tileNeedsBufferedUpdate(UpdatableTile* tile)
+{
+    if (!tile->managedTexture()->isValid(m_tiler->tileSize(), m_textureFormat))
+        return false;
+
+    if (!tile->isDirty())
+        return false;
+
+    if (!tile->isInUseOnImpl)
+        return false;
+
+    return true;
+}
+
+void TiledLayerChromium::updateTiles(bool idle, int left, int top, int right, int bottom, CCTextureUpdater& updater, const CCOcclusionTracker* occlusion)
+{
+    createTextureUpdaterIfNeeded();
+
+    // Create tiles as needed, expanding a dirty rect to contain all
+    // the dirty regions currently being drawn. All dirty tiles that are to be painted
+    // get their updateRect set to dirtyRect and dirtyRect cleared. This way if
+    // invalidateRect is invoked during updateLayerRect we don't lose the request.
+    IntRect paintRect;
+    for (int j = top; j <= bottom; ++j) {
+        for (int i = left; i <= right; ++i) {
+            UpdatableTile* tile = tileAt(i, j);
+            if (!tile)
+                tile = createTile(i, j);
+
+            // Temporary diagnostic crash
+            if (!m_tiler)
+                CRASH();
+
+            if (!tile->managedTexture()->isValid(m_tiler->tileSize(), m_textureFormat)) {
+                // Sets the dirty rect to a full-sized tile with border texels.
+                tile->dirtyRect = m_tiler->tileRect(tile);
+            }
+
+            // When not idle painting, if the visible region of the tile is occluded, don't reserve a texture or update the tile.
+            // If any part of the tile is visible, then we need to update it so the tile is pushed to the impl thread.
+            if (!idle && occlusion) {
+                IntRect visibleTileRect = intersection(m_tiler->tileBounds(i, j), visibleLayerRect());
+                if (occlusion->occluded(this, visibleTileRect)) {
+                    ASSERT(!tile->updated);
+                    continue;
+                }
+            }
+
+            // We come through this function multiple times during a commit, and updated should be true if the tile is not culled
+            // any single time through the function.
+            tile->updated = true;
+
+            if (layerTreeHost() && layerTreeHost()->bufferedUpdates() && tileNeedsBufferedUpdate(tile)) {
+                // FIXME: Decide if partial update should be allowed based on cost
+                // of update. https://bugs.webkit.org/show_bug.cgi?id=77376
+                if (tileOnlyNeedsPartialUpdate(tile) && layerTreeHost()->requestPartialTextureUpdate())
+                    tile->partialUpdate = true;
+                else {
+                    layerTreeHost()->deleteTextureAfterCommit(tile->managedTexture()->steal());
+                    // Sets the dirty rect to a full-sized tile with border texels.
+                    tile->dirtyRect = m_tiler->tileRect(tile);
+                }
+            }
+
+            if (!tile->managedTexture()->reserve(m_tiler->tileSize(), m_textureFormat)) {
+                m_skipsIdlePaint = true;
+                if (!idle) {
+                    m_skipsDraw = true;
+                    m_tiler->reset();
+                }
+                return;
+            }
+
+            paintRect.unite(tile->dirtyRect);
+        }
+    }
+
+    // For tiles that were not culled, we are going to update the area currently marked as dirty. So
+    // clear that dirty area and mark it for update instead.
+    for (int j = top; j <= bottom; ++j) {
+        for (int i = left; i <= right; ++i) {
+            UpdatableTile* tile = tileAt(i, j);
+            // FIXME: This should not ever be null.
+            if (!tile)
+                continue;
+            if (tile->updated)
+                tile->copyAndClearDirty();
+            else if (!idle && occlusion && tile->isDirty())
+                occlusion->overdrawMetrics().didCullTileForUpload();
+        }
+    }
+
+    if (paintRect.isEmpty())
+        return;
+
+    if (occlusion)
+        occlusion->overdrawMetrics().didPaint(paintRect);
+
+    // The updateRect should be in layer space. So we have to convert the paintRect from content space to layer space.
+    m_updateRect = FloatRect(paintRect);
+    float widthScale = bounds().width() / static_cast<float>(contentBounds().width());
+    float heightScale = bounds().height() / static_cast<float>(contentBounds().height());
+    m_updateRect.scale(widthScale, heightScale);
+
+    // Calling prepareToUpdate() calls into WebKit to paint, which may have the side
+    // effect of disabling compositing, which causes our reference to the texture updater to be deleted.
+    // However, we can't free the memory backing the SkCanvas until the paint finishes,
+    // so we grab a local reference here to hold the updater alive until the paint completes.
+    RefPtr<LayerTextureUpdater> protector(textureUpdater());
+    IntRect paintedOpaqueRect;
+    textureUpdater()->prepareToUpdate(paintRect, m_tiler->tileSize(), contentsScale(), paintedOpaqueRect);
+    m_didPaint = true;
+
+    for (int j = top; j <= bottom; ++j) {
+        for (int i = left; i <= right; ++i) {
+            UpdatableTile* tile = tileAt(i, j);
+            // FIXME: This should not ever be null.
+            if (!tile)
+                continue;
+
+            IntRect tileRect = m_tiler->tileBounds(i, j);
+
+            if (!tile->updated)
+                continue;
+
+            // Use updateRect as the above loop copied the dirty rect for this frame to updateRect.
+            const IntRect& dirtyRect = tile->updateRect;
+            if (dirtyRect.isEmpty())
+                continue;
+
+            // Save what was painted opaque in the tile. Keep the old area if the paint didn't touch it, and didn't paint some
+            // other part of the tile opaque.
+            IntRect tilePaintedRect = intersection(tileRect, paintRect);
+            IntRect tilePaintedOpaqueRect = intersection(tileRect, paintedOpaqueRect);
+            if (!tilePaintedRect.isEmpty()) {
+                IntRect paintInsideTileOpaqueRect = intersection(tile->opaqueRect(), tilePaintedRect);
+                bool paintInsideTileOpaqueRectIsNonOpaque = !tilePaintedOpaqueRect.contains(paintInsideTileOpaqueRect);
+                bool opaquePaintNotInsideTileOpaqueRect = !tilePaintedOpaqueRect.isEmpty() && !tile->opaqueRect().contains(tilePaintedOpaqueRect);
+
+                if (paintInsideTileOpaqueRectIsNonOpaque || opaquePaintNotInsideTileOpaqueRect)
+                    tile->setOpaqueRect(tilePaintedOpaqueRect);
+            }
+
+            // sourceRect starts as a full-sized tile with border texels included.
+            IntRect sourceRect = m_tiler->tileRect(tile);
+            sourceRect.intersect(dirtyRect);
+            // Paint rect not guaranteed to line up on tile boundaries, so
+            // make sure that sourceRect doesn't extend outside of it.
+            sourceRect.intersect(paintRect);
+
+            tile->updateRect = sourceRect;
+
+            if (sourceRect.isEmpty())
+                continue;
+
+            tile->texture()->prepareRect(sourceRect);
+            if (occlusion)
+                occlusion->overdrawMetrics().didUpload(WebTransformationMatrix(), sourceRect, tile->opaqueRect());
+
+            const IntPoint anchor = m_tiler->tileRect(tile).location();
+
+            // Calculate tile-space rectangle to upload into.
+            IntRect destRect(IntPoint(sourceRect.x() - anchor.x(), sourceRect.y() - anchor.y()), sourceRect.size());
+            if (destRect.x() < 0)
+                CRASH();
+            if (destRect.y() < 0)
+                CRASH();
+
+            // Offset from paint rectangle to this tile's dirty rectangle.
+            IntPoint paintOffset(sourceRect.x() - paintRect.x(), sourceRect.y() - paintRect.y());
+            if (paintOffset.x() < 0)
+                CRASH();
+            if (paintOffset.y() < 0)
+                CRASH();
+            if (paintOffset.x() + destRect.width() > paintRect.width())
+                CRASH();
+            if (paintOffset.y() + destRect.height() > paintRect.height())
+                CRASH();
+
+            if (tile->partialUpdate)
+                updater.appendPartialUpdate(tile->texture(), sourceRect, destRect);
+            else
+                updater.appendUpdate(tile->texture(), sourceRect, destRect);
+        }
+    }
+}
+
+void TiledLayerChromium::reserveTextures()
+{
+    updateBounds();
+
+    const IntRect& layerRect = visibleLayerRect();
+    if (layerRect.isEmpty() || m_tiler->hasEmptyBounds())
+        return;
+
+    int left, top, right, bottom;
+    m_tiler->layerRectToTileIndices(layerRect, left, top, right, bottom);
+
+    createTextureUpdaterIfNeeded();
+    for (int j = top; j <= bottom; ++j) {
+        for (int i = left; i <= right; ++i) {
+            UpdatableTile* tile = tileAt(i, j);
+            if (!tile)
+                tile = createTile(i, j);
+
+            if (!tile->managedTexture()->isValid(m_tiler->tileSize(), m_textureFormat))
+                tile->dirtyRect = m_tiler->tileRect(tile);
+
+            if (!tile->managedTexture()->reserve(m_tiler->tileSize(), m_textureFormat))
+                return;
+        }
+    }
+}
+
+Region TiledLayerChromium::visibleContentOpaqueRegion() const
+{
+    if (m_skipsDraw)
+        return Region();
+    if (opaque())
+        return visibleLayerRect();
+    return m_tiler->opaqueRegionInLayerRect(visibleLayerRect());
+}
+
+void TiledLayerChromium::resetUpdateState()
+{
+    CCLayerTilingData::TileMap::const_iterator end = m_tiler->tiles().end();
+    for (CCLayerTilingData::TileMap::const_iterator iter = m_tiler->tiles().begin(); iter != end; ++iter) {
+        UpdatableTile* tile = static_cast<UpdatableTile*>(iter->second.get());
+        // FIXME: This should not ever be null.
+        if (!tile)
+            continue;
+        tile->updateRect = IntRect();
+        tile->partialUpdate = false;
+        tile->updated = false;
+    }
+}
+
+void TiledLayerChromium::updateLayerRect(CCTextureUpdater& updater, const IntRect& layerRect, const CCOcclusionTracker* occlusion)
+{
+    m_skipsDraw = false;
+    m_skipsIdlePaint = false;
+    m_didPaint = false;
+
+    updateBounds();
+
+    resetUpdateState();
+
+    if (layerRect.isEmpty() || m_tiler->hasEmptyBounds())
+        return;
+
+    int left, top, right, bottom;
+    m_tiler->layerRectToTileIndices(layerRect, left, top, right, bottom);
+
+    updateTiles(false, left, top, right, bottom, updater, occlusion);
+}
+
+void TiledLayerChromium::idleUpdateLayerRect(CCTextureUpdater& updater, const IntRect& layerRect, const CCOcclusionTracker* occlusion)
+{
+    // Abort if we have already painted or run out of memory.
+    if (m_skipsIdlePaint || m_didPaint)
+        return;
+
+    ASSERT(m_tiler);
+
+    updateBounds();
+
+    if (m_tiler->hasEmptyBounds())
+        return;
+
+    IntRect idlePaintLayerRect = idlePaintRect(layerRect);
+    if (idlePaintLayerRect.isEmpty())
+        return;
+
+    // Protect any textures in the pre-paint area, as we would steal them from other layers
+    // over time anyhow. This ensures we don't lose tiles in the first rounds of idle painting
+    // that we have already painted.
+    protectTileTextures(idlePaintLayerRect);
+
+    int prepaintLeft, prepaintTop, prepaintRight, prepaintBottom;
+    m_tiler->layerRectToTileIndices(idlePaintLayerRect, prepaintLeft, prepaintTop, prepaintRight, prepaintBottom);
+
+    // If the layer is not visible, we have nothing to expand from, so instead we prepaint the outer-most set of tiles.
+    if (layerRect.isEmpty()) {
+        updateTiles(true, prepaintLeft, prepaintTop, prepaintRight, prepaintTop, updater, 0);
+        if (m_didPaint || m_skipsIdlePaint)
+            return;
+        updateTiles(true, prepaintLeft, prepaintBottom, prepaintRight, prepaintBottom, updater, 0);
+        if (m_didPaint || m_skipsIdlePaint)
+            return;
+        updateTiles(true, prepaintLeft, prepaintTop, prepaintLeft, prepaintBottom, updater, 0);
+        if (m_didPaint || m_skipsIdlePaint)
+            return;
+        updateTiles(true, prepaintRight, prepaintTop, prepaintRight, prepaintBottom, updater, 0);
+        return;
+    }
+
+    int left, top, right, bottom;
+    m_tiler->layerRectToTileIndices(layerRect, left, top, right, bottom);
+
+    // Otherwise, prepaint anything that was occluded but inside the layer's visible region.
+    updateTiles(true, left, top, right, bottom, updater, 0);
+    if (m_didPaint || m_skipsIdlePaint)
+        return;
+
+    // Then expand outwards from the visible area until we find a dirty row or column to update.
+    while (!m_skipsIdlePaint && (left > prepaintLeft || top > prepaintTop || right < prepaintRight || bottom < prepaintBottom)) {
+        if (bottom < prepaintBottom) {
+            ++bottom;
+            updateTiles(true, left, bottom, right, bottom, updater, 0);
+            if (m_didPaint || m_skipsIdlePaint)
+                break;
+        }
+        if (top > prepaintTop) {
+            --top;
+            updateTiles(true, left, top, right, top, updater, 0);
+            if (m_didPaint || m_skipsIdlePaint)
+                break;
+        }
+        if (left > prepaintLeft) {
+            --left;
+            updateTiles(true, left, top, left, bottom, updater, 0);
+            if (m_didPaint || m_skipsIdlePaint)
+                break;
+        }
+        if (right < prepaintRight) {
+            ++right;
+            updateTiles(true, right, top, right, bottom, updater, 0);
+            if (m_didPaint || m_skipsIdlePaint)
+                break;
+        }
+    }
+}
+
+bool TiledLayerChromium::needsIdlePaint(const IntRect& layerRect)
+{
+    if (m_skipsIdlePaint)
+        return false;
+
+    if (m_tiler->hasEmptyBounds())
+        return false;
+
+    IntRect idlePaintLayerRect = idlePaintRect(layerRect);
+    if (idlePaintLayerRect.isEmpty())
+        return false;
+
+    int left, top, right, bottom;
+    m_tiler->layerRectToTileIndices(idlePaintLayerRect, left, top, right, bottom);
+    for (int j = top; j <= bottom; ++j) {
+        for (int i = left; i <= right; ++i) {
+            // If the layerRect is empty, then we are painting the outer-most set of tiles only.
+            if (layerRect.isEmpty() && i != left && i != right && j != top && j != bottom)
+                continue;
+            UpdatableTile* tile = tileAt(i, j);
+            if (!tile || !tile->managedTexture()->isValid(m_tiler->tileSize(), m_textureFormat) || tile->isDirty())
+                return true;
+        }
+    }
+    return false;
+}
+
+IntRect TiledLayerChromium::idlePaintRect(const IntRect& visibleLayerRect)
+{
+    // For layers that are animating transforms but not visible at all, we don't know what part
+    // of them is going to become visible. For small layers we return the entire layer, for larger
+    // ones we avoid prepainting the layer at all.
+    if (visibleLayerRect.isEmpty()) {
+        bool isSmallLayer = m_tiler->numTilesX() <= 9 && m_tiler->numTilesY() <= 9 && m_tiler->numTilesX() * m_tiler->numTilesY() <= 9;
+        if ((drawTransformIsAnimating() || screenSpaceTransformIsAnimating()) && isSmallLayer)
+            return IntRect(IntPoint(), contentBounds());
+        return IntRect();
+    }
+
+    IntRect prepaintRect = visibleLayerRect;
+    // FIXME: This can be made a lot larger if we can:
+    // - reserve memory at a lower priority than for visible content
+    // - only reserve idle paint tiles up to a memory reclaim threshold and
+    // - insure we play nicely with other layers
+    prepaintRect.inflateX(m_tiler->tileSize().width());
+    prepaintRect.inflateY(m_tiler->tileSize().height());
+    prepaintRect.intersect(IntRect(IntPoint::zero(), contentBounds()));
+    return prepaintRect;
+}
+
+}
+#endif // USE(ACCELERATED_COMPOSITING)