Smoother scrolling by preparing offscreen tiles (credit: Ben Murdoch)

Change-Id: I80c7757bfb85f0b45726f2fa2f18644d2493fced

5 files changed, 56 insertions, 33 deletions

diff --git a/WebCore/platform/graphics/android/GLWebViewState.cpp b/WebCore/platform/graphics/android/GLWebViewState.cpp
index 63fe730..38b747d 100644
--- a/WebCore/platform/graphics/android/GLWebViewState.cpp
+++ b/WebCore/platform/graphics/android/GLWebViewState.cpp
@@ -288,7 +288,8 @@ void GLWebViewState::setViewport(SkRect& viewport, float scale)
             static_cast<int>(ceilf(viewport.fRight * invTileContentWidth)),
             static_cast<int>(ceilf(viewport.fBottom * invTileContentHeight)));
 
-    int maxTextureCount = (m_viewportTileBounds.width()+1)*(m_viewportTileBounds.height()+1)*2;
+    int maxTextureCount = (m_viewportTileBounds.width() + TilesManager::instance()->expandedTileBoundsX() * 2 + 1) *
+            (m_viewportTileBounds.height() + TilesManager::instance()->expandedTileBoundsY() * 2 + 1) * 2;
     TilesManager::instance()->setMaxTextureCount(maxTextureCount);
     m_tiledPageA->updateBaseTileSize();
     m_tiledPageB->updateBaseTileSize();
diff --git a/WebCore/platform/graphics/android/TiledPage.cpp b/WebCore/platform/graphics/android/TiledPage.cpp
index b6d2205..620aa6f 100644
--- a/WebCore/platform/graphics/android/TiledPage.cpp
+++ b/WebCore/platform/graphics/android/TiledPage.cpp
@@ -244,43 +244,29 @@ void TiledPage::prepare(bool goingDown, bool goingLeft, const SkIRect& tileBound
     int nbTilesWidth = tileBounds.width();
     int nbTilesHeight = tileBounds.height();
 
-    const int lastTileX = tileBounds.fRight - 1;
-    const int lastTileY = tileBounds.fBottom - 1;
+    int lastTileX = tileBounds.fRight - 1;
+    int lastTileY = tileBounds.fBottom - 1;
 
     const int baseContentHeight = m_glWebViewState->baseContentHeight();
     const int baseContentWidth = m_glWebViewState->baseContentWidth();
 
     TileSet* highResSet = new TileSet(this, nbTilesHeight, nbTilesWidth);
 
+    // Expand number of tiles to allow tiles outside of viewport to be prepared for
+    // smoother scrolling.
     int nTilesToPrepare = nbTilesWidth * nbTilesHeight;
     int nMaxTilesPerPage = m_baseTileSize / 2;
-
-    // PREPARE OFF-SCREEN TILES FOR SMOOTHER SCROLLING
-    // if you are going down and you are not already at the bottom of the page
-    // go ahead and prepare the tiles just off-screen beneath the viewport.
-    // Ensure we have enough tiles to do this with.
-    if (nTilesToPrepare + nbTilesWidth <= nMaxTilesPerPage) {
-        if (goingDown && baseContentHeight > lastTileY * TilesManager::tileHeight())
-            nbTilesHeight++;
-        // if you are going up and you are not already at the top of the page go
-        // ahead and prepare the tiles just off-screen above the viewport.
-        else if (!goingDown && firstTileY > 0) {
-            firstTileY--;
-            nbTilesHeight++;
-        }
+    int expandX = TilesManager::instance()->expandedTileBoundsX();
+    int expandY = TilesManager::instance()->expandedTileBoundsY();
+    if (nTilesToPrepare + (nbTilesHeight * expandX * 2) <= nMaxTilesPerPage) {
+        firstTileX -= expandX;
+        lastTileX += expandX;
+        nbTilesWidth += expandX * 2;
     }
-
-    if (nTilesToPrepare + nbTilesHeight <= nMaxTilesPerPage) {
-        // if you are going right and you are not already at the edge of the page go
-        // ahead and prepare the tiles just off-screen to the right of the viewport.
-        if (!goingLeft && baseContentWidth > lastTileX * TilesManager::tileWidth())
-            nbTilesWidth++;
-        // if you are going left and you are not already at the edge of the page go
-        // ahead and prepare the tiles just off-screen to the left of the viewport.
-        else if (goingLeft && firstTileX > 0) {
-            firstTileX--;
-            nbTilesWidth++;
-        }
+    if (nTilesToPrepare + (nbTilesWidth * expandY * 2) <= nMaxTilesPerPage) {
+        firstTileY -= expandY;
+        lastTileY += expandY;
+        nbTilesHeight += expandY * 2;
     }
 
     // We chose to prepare tiles depending on the scroll direction. Tiles are
@@ -331,10 +317,16 @@ void TiledPage::draw(float transparency, const SkIRect& tileBounds)
     const float tileWidth = TilesManager::tileWidth() * m_invScale;
     const float tileHeight = TilesManager::tileHeight() * m_invScale;
 
+    SkIRect actualTileBounds = tileBounds;
+    actualTileBounds.fTop -= TilesManager::instance()->expandedTileBoundsY();
+    actualTileBounds.fBottom += TilesManager::instance()->expandedTileBoundsY();
+    actualTileBounds.fLeft -= TilesManager::instance()->expandedTileBoundsX();
+    actualTileBounds.fRight += TilesManager::instance()->expandedTileBoundsX();
+
     XLOG("WE DRAW %x (%.2f) with transparency %.2f", this, scale(), transparency);
     for (int j = 0; j < m_baseTileSize; j++) {
         BaseTile& tile = m_baseTiles[j];
-        if (tileBounds.contains(tile.x(), tile.y())) {
+        if (actualTileBounds.contains(tile.x(), tile.y())) {
 
             SkRect rect;
             rect.fLeft = tile.x() * tileWidth;
diff --git a/WebCore/platform/graphics/android/TilesManager.cpp b/WebCore/platform/graphics/android/TilesManager.cpp
index 81b0404..21162ff 100644
--- a/WebCore/platform/graphics/android/TilesManager.cpp
+++ b/WebCore/platform/graphics/android/TilesManager.cpp
@@ -54,9 +54,11 @@
 // one viewport, otherwise the allocation may stall.
 // We need n textures for one TiledPage, and another n textures for the
 // second page used when scaling.
-// In our case, we use 300x300 textures. On the tablet, this equals to
-// at least 24 (6 * 4) textures, hence 48.
-#define MAX_TEXTURE_ALLOCATION 48
+// In our case, we use 300x300 textures. On the tablet, this equates to
+// at least 5 * 3 = 15 textures. We can also enable offscreen textures
+#define EXPANDED_TILE_BOUNDS_X 1
+#define EXPANDED_TILE_BOUNDS_Y 4
+#define MAX_TEXTURE_ALLOCATION (5+EXPANDED_TILE_BOUNDS_X*2)*(3+EXPANDED_TILE_BOUNDS_Y*2)*2
 #define TILE_WIDTH 300
 #define TILE_HEIGHT 300
 
@@ -69,6 +71,7 @@ namespace WebCore {
 TilesManager::TilesManager()
     : m_layersMemoryUsage(0)
     , m_maxTextureCount(0)
+    , m_expandedTileBounds(false)
     , m_generatorReady(false)
 {
     XLOG("TilesManager ctor");
@@ -366,6 +369,14 @@ float TilesManager::tileHeight()
     return TILE_HEIGHT;
 }
 
+int TilesManager::expandedTileBoundsX() {
+    return m_expandedTileBounds ? EXPANDED_TILE_BOUNDS_X : 0;
+}
+
+int TilesManager::expandedTileBoundsY() {
+    return m_expandedTileBounds ? EXPANDED_TILE_BOUNDS_Y : 0;
+}
+
 TilesManager* TilesManager::instance()
 {
     if (!gInstance) {
diff --git a/WebCore/platform/graphics/android/TilesManager.h b/WebCore/platform/graphics/android/TilesManager.h
index 92306b5..de22242 100644
--- a/WebCore/platform/graphics/android/TilesManager.h
+++ b/WebCore/platform/graphics/android/TilesManager.h
@@ -90,9 +90,15 @@ public:
     void setMaxTextureCount(int max);
     static float tileWidth();
     static float tileHeight();
+    int expandedTileBoundsX();
+    int expandedTileBoundsY();
 
     void allocateTiles();
 
+    void setExpandedTileBounds(bool enabled) {
+        m_expandedTileBounds = enabled;
+    }
+
 private:
 
     TilesManager();
@@ -112,6 +118,7 @@ private:
     unsigned int m_totalMaxTextureSize;
 
     int m_maxTextureCount;
+    bool m_expandedTileBounds;
 
     bool m_generatorReady;
 
diff --git a/WebKit/android/jni/WebViewCore.cpp b/WebKit/android/jni/WebViewCore.cpp
index 3328acd..5a16461 100644
--- a/WebKit/android/jni/WebViewCore.cpp
+++ b/WebKit/android/jni/WebViewCore.cpp
@@ -108,6 +108,7 @@
 #include "SkPicture.h"
 #include "SkUtils.h"
 #include "Text.h"
+#include "TilesManager.h"
 #include "TypingCommand.h"
 #include "WebCoreFrameBridge.h"
 #include "WebFrameView.h"
@@ -4511,6 +4512,15 @@ static void AutoFillForm(JNIEnv* env, jobject obj, jint queryId)
 #endif
 }
 
+static void SetExpandedTileBounds(JNIEnv *env, jobject obj, jboolean enabled)
+{
+    WebViewCore* viewImpl = GET_NATIVE_VIEW(env, obj);
+    if (!viewImpl)
+        return;
+    TilesManager::instance()->setExpandedTileBounds(enabled);
+}
+
+
 // ----------------------------------------------------------------------------
 
 /*
@@ -4618,6 +4628,8 @@ static JNINativeMethod gJavaWebViewCoreMethods[] = {
         (void*) GetTouchHighlightRects },
     { "nativeAutoFillForm", "(I)V",
         (void*) AutoFillForm },
+    { "nativeSetExpandedTileBounds", "(Z)V",
+        (void*) SetExpandedTileBounds },
 };
 
 int registerWebViewCore(JNIEnv* env)