Support partial invalidation of tiles based on webkit's inval rect.

This CL reverts the rollback of the original CL now that we have
fixed bug #3165953.

This reverts commit 144ccd9c8dba05ffaa0ae598f9b70032050fc20e.

Change-Id: Ibb5254f652ed95aa3b7b71bf24a2578c51e74a70

13 files changed, 199 insertions, 205 deletions

diff --git a/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.cpp b/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.cpp
index 7cecddd..1a8e686 100644
--- a/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.cpp
+++ b/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.cpp
@@ -56,28 +56,27 @@ BackedDoubleBufferedTexture::~BackedDoubleBufferedTexture()
 
 TextureInfo* BackedDoubleBufferedTexture::producerLock()
 {
-    m_varLock.lock();
+    m_busyLock.lock();
     m_busy = true;
-    m_varLock.unlock();
+    m_busyLock.unlock();
     return DoubleBufferedTexture::producerLock();
 }
 
 void BackedDoubleBufferedTexture::producerRelease()
 {
     DoubleBufferedTexture::producerRelease();
-    android::Mutex::Autolock lock(m_varLock);
+    android::Mutex::Autolock lock(m_busyLock);
     m_busy = false;
 }
 
 void BackedDoubleBufferedTexture::producerReleaseAndSwap()
 {
     DoubleBufferedTexture::producerReleaseAndSwap();
-    android::Mutex::Autolock lock(m_varLock);
+    android::Mutex::Autolock lock(m_busyLock);
     m_busy = false;
 }
 
-void BackedDoubleBufferedTexture::producerUpdate(BaseTile* painter,
-        TextureInfo* textureInfo, PaintingInfo& info)
+void BackedDoubleBufferedTexture::producerUpdate(TextureInfo* textureInfo)
 {
     // no need to upload a texture since the bitmap is empty
     if (!m_bitmap.width() && !m_bitmap.height()) {
@@ -93,34 +92,9 @@ void BackedDoubleBufferedTexture::producerUpdate(BaseTile* painter,
         textureInfo->m_height = m_bitmap.height();
     }
 
-    m_varLock.lock();
-    // set the painting information for this texture
-    if (equalsIdTextureA(textureInfo->m_textureId))
-        m_paintingInfoA = info;
-    else if (equalsIdTextureB(textureInfo->m_textureId))
-        m_paintingInfoB = info;
-    m_varLock.unlock();
-
     producerReleaseAndSwap();
 }
 
-// Compare the current texture displayed with some PaintingInfo.
-bool BackedDoubleBufferedTexture::consumerTextureUpToDate(PaintingInfo& info)
-{
-    android::Mutex::Autolock lock(m_varLock);
-    if (isTextureAReadable())
-        return info == m_paintingInfoA;
-    return info == m_paintingInfoB;
-}
-
-bool BackedDoubleBufferedTexture::consumerTextureSimilar(PaintingInfo& info)
-{
-    android::Mutex::Autolock lock(m_varLock);
-    if (isTextureAReadable())
-        return info.similar(m_paintingInfoA);
-    return info.similar(m_paintingInfoB);
-}
-
 bool BackedDoubleBufferedTexture::acquire(BaseTile* owner)
 {
     if (m_owner == owner)
@@ -128,7 +102,7 @@ bool BackedDoubleBufferedTexture::acquire(BaseTile* owner)
 
     // if the writable texture is busy (i.e. currently being written to) then we
     // can't change the owner out from underneath that texture
-    android::Mutex::Autolock lock(m_varLock);
+    android::Mutex::Autolock lock(m_busyLock);
     if (!m_busy) {
         if (m_owner)
             m_owner->removeTexture();
diff --git a/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.h b/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.h
index 1faa110..6bbb97a 100644
--- a/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.h
+++ b/WebCore/platform/graphics/android/BackedDoubleBufferedTexture.h
@@ -36,42 +36,6 @@ namespace WebCore {
 
 class BaseTile;
 
-class PaintingInfo {
-public:
-    PaintingInfo() : m_x(-1), m_y(-1), m_webview(0), m_picture(0) { }
-    PaintingInfo(int x, int y, GLWebViewState* webview)
-        : m_x(x)
-        , m_y(y)
-        , m_webview(webview)
-        , m_picture(0)
-    {
-        if(webview)
-            m_picture = webview->currentPictureCounter();
-    }
-    bool operator==(const PaintingInfo& info)
-    {
-        return m_webview == info.m_webview
-            && m_x == info.m_x
-            && m_y == info.m_y
-            && m_picture == info.m_picture;
-    }
-    bool similar(const PaintingInfo& info)
-    {
-        return m_webview == info.m_webview
-            && m_x == info.m_x
-            && m_y == info.m_y;
-    }
-    void setPosition(int x, int y) { m_x = x; m_y = y; }
-    void setGLWebViewState(GLWebViewState* webview) { m_webview = webview; }
-    void setPictureUsed(unsigned int picture) { m_picture = picture; }
-
-private:
-    int m_x;
-    int m_y;
-    GLWebViewState* m_webview;
-    unsigned int m_picture;
-};
-
 // DoubleBufferedTexture using a SkBitmap as backing mechanism
 class BackedDoubleBufferedTexture : public DoubleBufferedTexture {
 public:
@@ -88,7 +52,7 @@ public:
 
     // updates the texture with current bitmap and releases (and if needed also
     // swaps) the texture.
-    void producerUpdate(BaseTile* painter, TextureInfo* textureInfo, PaintingInfo& info);
+    void producerUpdate(TextureInfo* textureInfo);
 
     // The level can be one of the following values:
     //  * -1 for an unused texture.
@@ -107,11 +71,7 @@ public:
     BaseTile* owner() { return m_owner; } // only used by the consumer thread
     SkCanvas* canvas() { return m_canvas; } // only used by the producer thread
 
-    // checks to see if the current readable texture equals the provided PaintingInfo
-    bool consumerTextureUpToDate(PaintingInfo& info);
-    // checks to see if the current readable texture is similar to the provided PaintingInfo
-    bool consumerTextureSimilar(PaintingInfo& info);
-
+    // This is to be only used for debugging on the producer thread
     bool busy() { return m_busy; }
 
 private:
@@ -120,12 +80,13 @@ private:
     int m_usedLevel;
     BaseTile* m_owner;
 
-    //The following values are shared among threads and use m_varLock to stay synced
-    PaintingInfo m_paintingInfoA;
-    PaintingInfo m_paintingInfoB;
+    // This values signals that the texture is currently in use by the consumer.
+    // This allows us to prevent the owner of the texture from changing while the
+    // consumer is holding a lock on the texture.
     bool m_busy;
-
-    android::Mutex m_varLock;
+    // We mutex protect the reads/writes of m_busy to ensure that we are reading
+    // the most up-to-date value even across processors in an SMP system.
+    android::Mutex m_busyLock;
 };
 
 } // namespace WebCore
diff --git a/WebCore/platform/graphics/android/BaseTile.cpp b/WebCore/platform/graphics/android/BaseTile.cpp
index 5ab801e..ff5d9ca 100644
--- a/WebCore/platform/graphics/android/BaseTile.cpp
+++ b/WebCore/platform/graphics/android/BaseTile.cpp
@@ -72,6 +72,9 @@ BaseTile::BaseTile(TiledPage* page, int x, int y)
     , m_y(y)
     , m_texture(0)
     , m_scale(1)
+    , m_dirty(true)
+    , m_lastDirtyPicture(0)
+    , m_lastPaintedPicture(0)
 {
 #ifdef DEBUG_COUNT
     gBaseTileCount++;
@@ -80,6 +83,7 @@ BaseTile::BaseTile(TiledPage* page, int x, int y)
 
 BaseTile::~BaseTile()
 {
+    setUsedLevel(-1);
 #ifdef DEBUG_COUNT
     gBaseTileCount--;
 #endif
@@ -90,26 +94,43 @@ BaseTile::~BaseTile()
 void BaseTile::reserveTexture()
 {
     BackedDoubleBufferedTexture* texture = TilesManager::instance()->getAvailableTexture(this);
-    // We update atomically, so paintBitmap() can see the correct value
-    android_atomic_acquire_store((int32_t)texture, (int32_t*)&m_texture);
-    XLOG("%x (%d, %d) reserveTexture res: %x...", this, x(), y(), m_texture);
+
+    android::AutoMutex lock(m_atomicSync);
+    if (m_texture != texture) {
+        m_lastPaintedPicture = 0;
+        m_dirty = true;
+    }
+    m_texture = texture;
 }
 
 void BaseTile::removeTexture()
 {
     XLOG("%x removeTexture res: %x...", this, m_texture);
     // We update atomically, so paintBitmap() can see the correct value
-    android_atomic_acquire_store(0, (int32_t*)&m_texture);
+    android::AutoMutex lock(m_atomicSync);
+    m_texture = 0;
 }
 
 void BaseTile::setScale(float scale)
 {
+    android::AutoMutex lock(m_atomicSync);
+    if (m_scale != scale)
+        m_dirty = true;
     m_scale = scale;
-    // FIXME: the following two lines force a memory barrier which causes
-    // m_scale to be observable on other cores. We should replace this
-    // with a dedicated system function if/when available.
-    int32_t tempValue = 0;
-    android_atomic_acquire_load(&tempValue);
+}
+
+void BaseTile::markAsDirty(int unsigned pictureCount)
+{
+    android::AutoMutex lock(m_atomicSync);
+    m_lastDirtyPicture = pictureCount;
+    if (m_lastPaintedPicture < m_lastDirtyPicture)
+        m_dirty = true;
+}
+
+bool BaseTile::isDirty()
+{
+    android::AutoMutex lock(m_atomicSync);
+    return m_dirty;
 }
 
 void BaseTile::setUsedLevel(int usedLevel)
@@ -120,13 +141,13 @@ void BaseTile::setUsedLevel(int usedLevel)
 
 void BaseTile::draw(float transparency, SkRect& rect)
 {
+    // No need to mutex protect reads of m_texture as it is only written to by
+    // the consumer thread.
     if (!m_texture) {
         XLOG("%x (%d, %d) trying to draw, but no m_texture!", this, x(), y());
         return;
     }
 
-    PaintingInfo info(m_x, m_y, m_page->glWebViewState());
-
     TextureInfo* textureInfo = m_texture->consumerLock();
     if (!textureInfo) {
         XLOG("%x (%d, %d) trying to draw, but no textureInfo!", this, x(), y());
@@ -134,61 +155,57 @@ void BaseTile::draw(float transparency, SkRect& rect)
         return;
     }
 
-    if (m_texture->consumerTextureSimilar(info)) {
+    m_atomicSync.lock();
+    bool isTexturePainted = m_lastPaintedPicture;
+    m_atomicSync.unlock();
+
+    if (isTexturePainted)
         TilesManager::instance()->shader()->drawQuad(rect, textureInfo->m_textureId,
                                                      transparency);
-    }
 
     m_texture->consumerRelease();
 }
 
-bool BaseTile::isBitmapReady()
+bool BaseTile::isTileReady()
 {
     if (!m_texture)
         return false;
     if (m_texture->owner() != this)
         return false;
-    PaintingInfo info(m_x, m_y, m_page->glWebViewState());
-    return m_texture->consumerTextureUpToDate(info);
+
+    android::AutoMutex lock(m_atomicSync);
+    return !m_dirty;
 }
 
 // This is called from the texture generation thread
 void BaseTile::paintBitmap()
 {
-    const int x = m_x;
-    const int y = m_y;
-    TiledPage* tiledPage = m_page;
-
-    // We acquire the texture atomically. Once we have it, we
-    // can continue with it, and m_texture can be updated without
-    // consequences.
-    BackedDoubleBufferedTexture* texture = reinterpret_cast<BackedDoubleBufferedTexture*>(
-        android_atomic_release_load((int32_t*)&m_texture));
 
-    // The loading of m_texture forces the execution of a memory barrier,
-    // which ensures that we are observing the most recent value of m_scale
-    // written by another core.
+    // We acquire the values below atomically. This ensures that we are reading
+    // values correctly across cores. Further, once we have these values they
+    // can be updated by other threads without consequence.
+    m_atomicSync.lock();
+    bool dirty = m_dirty;
+    BackedDoubleBufferedTexture* texture = m_texture;
     float scale = m_scale;
+    m_atomicSync.unlock();
 
-    if (!texture)
+    if(!dirty || !texture)
         return;
 
+    const int x = m_x;
+    const int y = m_y;
+    TiledPage* tiledPage = m_page;
+
     TextureInfo* textureInfo = texture->producerLock();
 
-    // at this point we can safely check the ownership
-    // (if the texture got transferred to another BaseTile
-    // under us)
+    // at this point we can safely check the ownership (if the texture got
+    // transferred to another BaseTile under us)
     if (texture->owner() != this || texture->usedLevel() > 1) {
         texture->producerRelease();
         return;
     }
 
-    PaintingInfo info(x, y, tiledPage->glWebViewState());
-    if (texture->consumerTextureUpToDate(info)) {
-        texture->producerRelease();
-        return;
-    }
-
     float tileWidth = textureInfo->m_width;
     float tileHeight = textureInfo->m_height;
 
@@ -203,7 +220,7 @@ void BaseTile::paintBitmap()
     canvas->scale(scale, scale);
     canvas->translate(-x * w, -y * h);
 
-    tiledPage->paintBaseLayerContent(canvas);
+    unsigned int pictureCount = tiledPage->paintBaseLayerContent(canvas);
 
     canvas->restore();
 
@@ -219,7 +236,13 @@ void BaseTile::paintBitmap()
     canvas->drawLine(tileWidth, 0, tileWidth, tileHeight, paint);
 #endif
 
-    texture->producerUpdate(this, textureInfo, info);
+    texture->producerUpdate(textureInfo);
+
+    m_atomicSync.lock();
+    m_lastPaintedPicture = pictureCount;
+    if (m_lastPaintedPicture >= m_lastDirtyPicture)
+        m_dirty = false;
+    m_atomicSync.unlock();
 }
 
 } // namespace WebCore
diff --git a/WebCore/platform/graphics/android/BaseTile.h b/WebCore/platform/graphics/android/BaseTile.h
index 429d950..8870cbf 100644
--- a/WebCore/platform/graphics/android/BaseTile.h
+++ b/WebCore/platform/graphics/android/BaseTile.h
@@ -36,6 +36,7 @@
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 #include <GLES2/gl2.h>
+#include <utils/threads.h>
 
 namespace WebCore {
 
@@ -69,12 +70,15 @@ public:
     void reserveTexture();
     void removeTexture();
     void setUsedLevel(int);
-    bool isBitmapReady();
+    bool isTileReady();
     void draw(float transparency, SkRect& rect);
 
     // the only thread-safe function called by the background thread
     void paintBitmap();
 
+    void markAsDirty(const unsigned int pictureCount);
+    bool isDirty();
+
     float scale() const { return m_scale; }
     void setScale(float scale);
 
@@ -89,9 +93,25 @@ private:
     int m_x;
     int m_y;
 
-    // these variables can be updated throughout the lifetime of the object
+    // The remaining variables can be updated throughout the lifetime of the object
     BackedDoubleBufferedTexture* m_texture;
     float m_scale;
+    // used to signal that the that the tile is out-of-date and needs to be redrawn
+    bool m_dirty;
+    // stores the id of the latest picture from webkit that caused this tile to
+    // become dirty. A tile is no longer dirty when it has been painted with a
+    // picture that is newer than this value.
+    unsigned int m_lastDirtyPicture;
+    // stores the id of the latest picture painted to the tile. If the id is 0
+    // then we know that the picture has not yet been painted an there is nothing
+    // to display (dirty or otherwise).
+    unsigned int m_lastPaintedPicture;
+
+    // This mutex serves two purposes. (1) It ensures that certain operations
+    // happen atomically and (2) it makes sure those operations are synchronized
+    // across all threads and cores.
+    android::Mutex m_atomicSync;
+
 };
 
 } // namespace WebCore
diff --git a/WebCore/platform/graphics/android/DoubleBufferedTexture.h b/WebCore/platform/graphics/android/DoubleBufferedTexture.h
index d16d5f3..2b2fd03 100644
--- a/WebCore/platform/graphics/android/DoubleBufferedTexture.h
+++ b/WebCore/platform/graphics/android/DoubleBufferedTexture.h
@@ -50,11 +50,6 @@ public:
     TextureInfo* consumerLock();
     void consumerRelease();
 
-protected:
-    bool equalsIdTextureA(GLuint id) { return id == m_textureA.getSourceTextureId(); }
-    bool equalsIdTextureB(GLuint id) { return id == m_textureB.getSourceTextureId(); }
-    bool isTextureAReadable() { return getReadableTexture() == &m_textureA; }
-
 private:
     SharedTexture* getReadableTexture();
     SharedTexture* getWriteableTexture();
diff --git a/WebCore/platform/graphics/android/GLWebViewState.cpp b/WebCore/platform/graphics/android/GLWebViewState.cpp
index e1e517c..4ad22d8 100644
--- a/WebCore/platform/graphics/android/GLWebViewState.cpp
+++ b/WebCore/platform/graphics/android/GLWebViewState.cpp
@@ -81,7 +81,6 @@ GLWebViewState::GLWebViewState()
     , m_extra(0)
     , m_navLayer(0)
 {
-    m_invalidatedRect.setEmpty();
     m_tiledPageA = new TiledPage(FIRST_TILED_PAGE_ID, this);
     m_tiledPageB = new TiledPage(SECOND_TILED_PAGE_ID, this);
 #ifdef DEBUG_COUNT
@@ -108,8 +107,13 @@ void GLWebViewState::setBaseLayer(BaseLayerAndroid* layer, IntRect& rect)
     m_navLayer = 0;
     if (m_baseLayer) {
         m_baseLayer->setGLWebViewState(this);
-        m_invalidatedRect.set(rect);
         m_currentPictureCounter++;
+
+        if (!rect.isEmpty()) {
+            // find which tiles fall within the invalRect and mark them as dirty
+            m_tiledPageA->invalidateRect(rect, m_currentPictureCounter);
+            m_tiledPageB->invalidateRect(rect, m_currentPictureCounter);
+        }
     }
 }
 
@@ -132,7 +136,7 @@ void GLWebViewState::resetExtra(bool repaint)
     m_navLayer = 0;
 }
 
-void GLWebViewState::paintBaseLayerContent(SkCanvas* canvas)
+unsigned int GLWebViewState::paintBaseLayerContent(SkCanvas* canvas)
 {
     android::Mutex::Autolock lock(m_baseLayerLock);
     if (m_baseLayer) {
@@ -140,6 +144,7 @@ void GLWebViewState::paintBaseLayerContent(SkCanvas* canvas)
         if (m_extra && m_navLayer)
             m_extra->draw(canvas, m_navLayer);
     }
+    return m_currentPictureCounter;
 }
 
 void GLWebViewState::scheduleUpdate(const double& currentTime, float scale)
diff --git a/WebCore/platform/graphics/android/GLWebViewState.h b/WebCore/platform/graphics/android/GLWebViewState.h
index 95bc07d..3eaabb3 100644
--- a/WebCore/platform/graphics/android/GLWebViewState.h
+++ b/WebCore/platform/graphics/android/GLWebViewState.h
@@ -95,8 +95,9 @@ class LayerAndroid;
 // get the GL textures from an existing pool, and reuse them.
 //
 // The way we do it is that when we call TiledPage::prepare(), we group the
-// tiles we need into a TilesSet, call TilesSet::reserveTextures() (which
-// associates the GL textures to the BaseTiles).
+// tiles we need (i.e. in the viewport and dirty) into a TilesSet and call
+// BaseTile::reserveTexture() for each tile (which ensures there is a specific
+// GL textures backing the BaseTiles).
 //
 // reserveTexture() will ask the TilesManager for a texture. The allocation
 // mechanism goal is to (in order):
@@ -104,8 +105,22 @@ class LayerAndroid;
 // - prefers to allocate textures that are as far from the viewport as possible
 // - prefers to allocate textures that are used by different TiledPages
 //
-// Note that to compute the distance of tiles, each time we prepare() a
-// TiledPage, we compute the distance of the tiles in it from the viewport.
+// Note that to compute the distance of each tile from the viewport, each time
+// we prepare() a TiledPage. Also during each prepare() we compute which tiles
+// are dirty based on the info we have received from webkit.
+//
+// BaseTile Invalidation
+// ------------------
+//
+// We do not want to redraw a tile if the tile is up-to-date. A tile is
+// considered to be dirty an in need of redrawing in the following cases
+//  - the tile has acquires a new texture
+//  - webkit invalidates all or part of the tiles contents
+//
+// To handle the case of webkit invalidation we store two ids (counters) of the
+// pictureSets in the tile.  The first id (A) represents the pictureSet used to
+// paint the tile and the second id (B) represents the pictureSet in which the
+// tile was invalidated by webkit. Thus, if A < B then tile is dirty.
 //
 // Painting scheduling
 // -------------------
@@ -155,7 +170,7 @@ public:
     int originalTilesPosY() const { return m_originalTilesPosY; }
     void setOriginalTilesPosY(int pos) { m_originalTilesPosY = pos; }
 
-    void paintBaseLayerContent(SkCanvas* canvas);
+    unsigned int paintBaseLayerContent(SkCanvas* canvas);
     void setBaseLayer(BaseLayerAndroid* layer, IntRect& rect);
     void setExtra(android::DrawExtra* extra, LayerAndroid* navLayer);
     void resetExtra(bool repaint);
@@ -176,7 +191,6 @@ public:
     int firstTileY() const { return m_firstTileY; }
 
     unsigned int currentPictureCounter() const { return m_currentPictureCounter; }
-    SkRect& invalidatedRect() { return m_invalidatedRect; }
 
 private:
 
@@ -207,7 +221,6 @@ private:
     android::Mutex m_baseLayerLock;
     BaseLayerAndroid* m_baseLayer;
     unsigned int m_currentPictureCounter;
-    SkRect m_invalidatedRect;
     bool m_usePageA;
     TiledPage* m_tiledPageA;
     TiledPage* m_tiledPageB;
diff --git a/WebCore/platform/graphics/android/TexturesGenerator.cpp b/WebCore/platform/graphics/android/TexturesGenerator.cpp
index f81a297..193ca46 100644
--- a/WebCore/platform/graphics/android/TexturesGenerator.cpp
+++ b/WebCore/platform/graphics/android/TexturesGenerator.cpp
@@ -53,10 +53,13 @@ void TexturesGenerator::schedulePaintForTileSet(TileSet* set)
 {
     android::Mutex::Autolock lock(mRequestedPixmapsLock);
     for (unsigned int i = 0; i < mRequestedPixmaps.size(); i++) {
-        TileSet* s = mRequestedPixmaps[i];
-        if (s && *s == *set) {
-            // Similar set already in the queue
-            delete set;
+        TileSet** s = &mRequestedPixmaps[i];
+        // A similar set is already in the queue. The newer set may have additional
+        // dirty tiles so delete the existing set and replace it with the new one.
+        if (*s && **s == *set) {
+            TileSet* oldSet = *s;
+            *s = set;
+            delete oldSet;
             return;
         }
     }
diff --git a/WebCore/platform/graphics/android/TileSet.cpp b/WebCore/platform/graphics/android/TileSet.cpp
index fe13ef3..4530640 100644
--- a/WebCore/platform/graphics/android/TileSet.cpp
+++ b/WebCore/platform/graphics/android/TileSet.cpp
@@ -56,10 +56,8 @@ int TileSet::count()
 }
 #endif
 
-TileSet::TileSet(int id, int firstTileX, int firstTileY, int rows, int cols)
-    : m_id(id)
-    , m_firstTileX(firstTileX)
-    , m_firstTileY(firstTileY)
+TileSet::TileSet(TiledPage* tiledPage, int rows, int cols)
+    : m_tiledPage(tiledPage)
     , m_nbRows(rows)
     , m_nbCols(cols)
 {
@@ -77,36 +75,12 @@ TileSet::~TileSet()
 
 bool TileSet::operator==(const TileSet& set)
 {
-    return m_id == set.m_id
-           && m_firstTileX == set.m_firstTileX
-           && m_firstTileY == set.m_firstTileY
+    return m_tiledPage == set.m_tiledPage
            && m_nbRows == set.m_nbRows
            && m_nbCols == set.m_nbCols;
 }
 
 
-void TileSet::reserveTextures()
-{
-#ifdef DEBUG
-    if (m_tiles.size()) {
-        TiledPage* page = m_tiles[0]->page();
-        XLOG("reserveTextures (%d tiles) for page %x (sibling: %x)", m_tiles.size(), page, page->sibling());
-        TilesManager::instance()->printTextures();
-    }
-#endif // DEBUG
-
-    for (unsigned int i = 0; i < m_tiles.size(); i++)
-        m_tiles[i]->reserveTexture();
-
-#ifdef DEBUG
-    if (m_tiles.size()) {
-        TiledPage* page = m_tiles[0]->page();
-        XLOG(" DONE reserveTextures (%d tiles) for page %x (sibling: %x)", m_tiles.size(), page, page->sibling());
-        TilesManager::instance()->printTextures();
-    }
-#endif // DEBUG
-}
-
 void TileSet::paint()
 {
     XLOG("%x, painting %d tiles", this, m_tiles.size());
diff --git a/WebCore/platform/graphics/android/TileSet.h b/WebCore/platform/graphics/android/TileSet.h
index adf6d13..fd65ad7 100644
--- a/WebCore/platform/graphics/android/TileSet.h
+++ b/WebCore/platform/graphics/android/TileSet.h
@@ -45,11 +45,10 @@ public:
 #ifdef DEBUG_COUNT
     static int count();
 #endif
-    TileSet(int id, int firstTileX, int firstTileY, int rows, int cols);
+    TileSet(TiledPage* tiledPage, int nbRows, int nbCols);
     ~TileSet();
 
     bool operator==(const TileSet& set);
-    void reserveTextures();
     void paint();
 
     void add(BaseTile* texture)
@@ -59,17 +58,13 @@ public:
 
     TiledPage* page()
     {
-        if (m_tiles.size())
-            return m_tiles[0]->page();
-        return 0;
+        return m_tiledPage;
     }
 
 private:
     Vector<BaseTile*> m_tiles;
 
-    int m_id;
-    int m_firstTileX;
-    int m_firstTileY;
+    TiledPage* m_tiledPage;
     int m_nbRows;
     int m_nbCols;
 };
diff --git a/WebCore/platform/graphics/android/TiledPage.cpp b/WebCore/platform/graphics/android/TiledPage.cpp
index 6430b02..358c1a8 100644
--- a/WebCore/platform/graphics/android/TiledPage.cpp
+++ b/WebCore/platform/graphics/android/TiledPage.cpp
@@ -29,6 +29,7 @@
 #if USE(ACCELERATED_COMPOSITING)
 
 #include "GLUtils.h"
+#include "IntRect.h"
 #include "TilesManager.h"
 
 #ifdef DEBUG
@@ -64,6 +65,7 @@ TiledPage::TiledPage(int id, GLWebViewState* state)
     , m_scale(1)
     , m_invScale(1)
     , m_glWebViewState(state)
+    , m_latestPictureInval(0)
 {
 #ifdef DEBUG_COUNT
     gTilePageCount++;
@@ -94,6 +96,24 @@ BaseTile* TiledPage::getBaseTile(int x, int y)
     return m_baseTiles.get(key);
 }
 
+void TiledPage::invalidateRect(const IntRect& inval, const unsigned int pictureCount)
+{
+    // Given the current scale level we need to mark the appropriate tiles as dirty
+    TilesManager* manager = TilesManager::instance();
+    const float invTileContentWidth = m_scale / manager->tileWidth();
+    const float invTileContentHeight = m_scale / manager->tileHeight();
+
+    const int firstDirtyTileX = static_cast<int>(floorf(inval.x() * invTileContentWidth));
+    const int firstDirtyTileY = static_cast<int>(floorf(inval.y() * invTileContentHeight));
+    const int lastDirtyTileX = static_cast<int>(ceilf(inval.right() * invTileContentWidth));
+    const int lastDirtyTileY = static_cast<int>(ceilf(inval.bottom() * invTileContentHeight));
+
+    // We defer marking the tile as dirty until the next time we need to prepare
+    // to draw.
+    m_invalRegion.op(firstDirtyTileX, firstDirtyTileY, lastDirtyTileX, lastDirtyTileY, SkRegion::kUnion_Op);
+    m_latestPictureInval = pictureCount;
+}
+
 void TiledPage::prepareRow(bool goingLeft, int tilesInRow, int firstTileX, int y, TileSet* set)
 {
     if (y < 0)
@@ -119,11 +139,16 @@ void TiledPage::prepareRow(bool goingLeft, int tilesInRow, int firstTileX, int y
         }
         tile = m_baseTiles.get(key);
         tile->setScale(m_scale);
-        set->add(tile);
+
+        // ensure there is a texture associated with the tile and then check to
+        // see if the texture is dirty and in need of repainting
+        tile->reserveTexture();
+        if(tile->isDirty())
+            set->add(tile);
     }
 }
 
-void TiledPage::setTileLevels(int firstTileX, int firstTileY)
+void TiledPage::updateTileState(int firstTileX, int firstTileY)
 {
     if (!m_glWebViewState)
         return;
@@ -138,6 +163,11 @@ void TiledPage::setTileLevels(int firstTileX, int firstTileY)
         if(!tile)
             continue;
 
+        // if the tile is in the dirty region then we must invalidate it
+        if (m_invalRegion.contains(tile->x(), tile->y()))
+            tile->markAsDirty(m_latestPictureInval);
+
+        // set the used level of the tile (e.g. distance from the viewport)
         int dx = 0;
         int dy = 0;
 
@@ -156,6 +186,10 @@ void TiledPage::setTileLevels(int firstTileX, int firstTileY)
         XLOG("setTileLevel tile: %x, fxy(%d, %d), level: %d", tile, firstTileX, firstTileY, d);
         tile->setUsedLevel(d);
     }
+
+    // clear the invalidated region as all tiles within that region have now
+    // been marked as dirty.
+    m_invalRegion.setEmpty();
 }
 
 void TiledPage::prepare(bool goingDown, bool goingLeft, int firstTileX, int firstTileY)
@@ -163,10 +197,13 @@ void TiledPage::prepare(bool goingDown, bool goingLeft, int firstTileX, int firs
     if (!m_glWebViewState)
         return;
 
+    // update the tiles distance from the viewport
+    updateTileState(firstTileX, firstTileY);
+
     int nbTilesWidth = m_glWebViewState->nbTilesWidth();
     int nbTilesHeight = m_glWebViewState->nbTilesHeight();
 
-    TileSet* highResSet = new TileSet(m_id, firstTileX, firstTileY, nbTilesHeight, nbTilesWidth);
+    TileSet* highResSet = new TileSet(this, nbTilesHeight, nbTilesWidth);
 
     // We chose to display tiles depending on the scroll direction:
     if (goingDown) {
@@ -178,23 +215,6 @@ void TiledPage::prepare(bool goingDown, bool goingLeft, int firstTileX, int firs
             prepareRow(goingLeft, nbTilesWidth, firstTileX, startingTileY - i, highResSet);
     }
 
-    // update the tiles distance from the viewport
-    setTileLevels(firstTileX, firstTileY);
-
-
-#ifdef DEBUG
-    XLOG("+++ BEFORE RESERVE TEXTURES (%d x %d) at (%d, %d), TiledPage %x",
-         nbTilesWidth, nbTilesHeight, firstTileX, firstTileY, this);
-    TilesManager::instance()->printTextures();
-#endif // DEBUG
-    highResSet->reserveTextures();
-
-#ifdef DEBUG
-    TilesManager::instance()->printTextures();
-    XLOG("--- AFTER RESERVE TEXTURES (%d x %d) at (%d, %d), TiledPage %x",
-         nbTilesWidth, nbTilesHeight, firstTileX, firstTileY, this);
-#endif // DEBUG
-
     // schedulePaintForTileSet will take ownership of the highResSet here,
     // so no delete necessary.
     TilesManager::instance()->schedulePaintForTileSet(highResSet);
@@ -213,7 +233,7 @@ bool TiledPage::ready(int firstTileX, int firstTileY)
             int x = j + firstTileX;
             int y = i + firstTileY;
             BaseTile* t = getBaseTile(x, y);
-            if (!t || !t->isBitmapReady())
+            if (!t || !t->isTileReady())
                 return false;
         }
     }
@@ -260,10 +280,11 @@ void TiledPage::draw(float transparency, SkRect& viewport, int firstTileX, int f
 #endif // DEBUG
 }
 
-void TiledPage::paintBaseLayerContent(SkCanvas* canvas)
+unsigned int TiledPage::paintBaseLayerContent(SkCanvas* canvas)
 {
     if (m_glWebViewState)
-        m_glWebViewState->paintBaseLayerContent(canvas);
+        return m_glWebViewState->paintBaseLayerContent(canvas);
+    return 0;
 }
 
 TiledPage* TiledPage::sibling()
diff --git a/WebCore/platform/graphics/android/TiledPage.h b/WebCore/platform/graphics/android/TiledPage.h
index 8be2361..b532033 100644
--- a/WebCore/platform/graphics/android/TiledPage.h
+++ b/WebCore/platform/graphics/android/TiledPage.h
@@ -30,11 +30,13 @@
 
 #include "BaseTile.h"
 #include "SkCanvas.h"
+#include "SkRegion.h"
 #include "TileSet.h"
 
 namespace WebCore {
 
 class GLWebViewState;
+class IntRect;
 
 typedef std::pair<int, int> TileKey;
 typedef HashMap<TileKey, BaseTile*> TileMap;
@@ -68,15 +70,17 @@ public:
     void draw(float transparency, SkRect& viewport, int firstTileX, int firstTileY);
 
     // used by individual tiles to generate the bitmap for their tile
-    void paintBaseLayerContent(SkCanvas*);
+    unsigned int paintBaseLayerContent(SkCanvas*);
     // used by individual tiles to get the information about the current picture
     GLWebViewState* glWebViewState() { return m_glWebViewState; }
 
     float scale() const { return m_scale; }
     void setScale(float scale) { m_scale = scale; m_invScale = 1 / scale; }
 
+    void invalidateRect(const IntRect& invalRect, const unsigned int pictureCount);
+
 private:
-    void setTileLevels(int firstTileX, int firstTileY);
+    void updateTileState(int firstTileX, int firstTileY);
     void prepareRow(bool goingLeft, int tilesInRow, int firstTileX, int y, TileSet* set);
 
     BaseTile* getBaseTile(int x, int y);
@@ -86,6 +90,13 @@ private:
     float m_scale;
     float m_invScale;
     GLWebViewState* m_glWebViewState;
+
+    // used to identify the tiles that have been invalidated (marked dirty) since
+    // the last time updateTileState() has been called. The region is stored in
+    // terms of the (x,y) coordinates used to determine the location of the tile
+    // within the page, not in content/view pixel coordinates.
+    SkRegion m_invalRegion;
+    unsigned int m_latestPictureInval;
 };
 
 } // namespace WebCore
diff --git a/WebCore/platform/graphics/android/TilesManager.cpp b/WebCore/platform/graphics/android/TilesManager.cpp
index 54ca9ad..9ebfe02 100644
--- a/WebCore/platform/graphics/android/TilesManager.cpp
+++ b/WebCore/platform/graphics/android/TilesManager.cpp
@@ -136,8 +136,7 @@ void TilesManager::paintTexturesDefault()
 #else
             canvas->drawARGB(255, 255, 255, 255);
 #endif // DEBUG
-            PaintingInfo info;
-            texture->producerUpdate(0, textureInfo, info);
+            texture->producerUpdate(textureInfo);
         }
     }
 }
@@ -186,9 +185,9 @@ BackedDoubleBufferedTexture* TilesManager::getAvailableTexture(BaseTile* owner)
         }
     }
     if (farthestTexture && farthestTexture->acquire(owner)) {
-        farthestTexture->setUsedLevel(0);
         XLOG("farthest texture, getAvailableTexture(%x) => texture %x (level %d)",
              owner, farthestTexture, farthestTexture->usedLevel());
+        farthestTexture->setUsedLevel(0);
         return farthestTexture;
     }