Fix layer tile allocation to be more consistent, less disco

bug:5290559

Two major things:

* Avoid swapping front/back textures before the textures have been blitted to
  avoid race condition where blit fails because it doesn't see a back texture

* Don't allow a tile to acquire its front texture to paint into, as the
  acquisition logic doesn't handle this.

Change-Id: I84b59396ca9faaf3ddc7c75b6f66e4736bf4c3cf

4 files changed, 34 insertions, 17 deletions

diff --git a/Source/WebCore/platform/graphics/android/BaseTile.cpp b/Source/WebCore/platform/graphics/android/BaseTile.cpp
index 8a4c2d5..dc17a21 100644
--- a/Source/WebCore/platform/graphics/android/BaseTile.cpp
+++ b/Source/WebCore/platform/graphics/android/BaseTile.cpp
@@ -70,7 +70,7 @@ BaseTile::BaseTile(bool isLayerTile)
     , m_lastDirtyPicture(0)
     , m_isTexturePainted(false)
     , m_isLayerTile(isLayerTile)
-    , m_isSwapNeeded(false)
+    , m_swapDrawCount(0)
     , m_drawCount(0)
 {
 #ifdef DEBUG_COUNT
@@ -133,7 +133,7 @@ void BaseTile::reserveTexture()
 
     android::AutoMutex lock(m_atomicSync);
     if (texture && m_backTexture != texture) {
-        m_isSwapNeeded = false; // no longer ready to swap
+        m_swapDrawCount = 0; // no longer ready to swap
         m_backTexture = texture;
 
         // this is to catch when the front texture is stolen from beneath us. We
@@ -240,7 +240,7 @@ bool BaseTile::isTileReady()
 {
     // Return true if the tile's most recently drawn texture is up to date
     android::AutoMutex lock(m_atomicSync);
-    BaseTileTexture * texture = m_isSwapNeeded ? m_backTexture : m_frontTexture;
+    BaseTileTexture * texture = m_swapDrawCount ? m_backTexture : m_frontTexture;
 
     if (!texture)
         return false;
@@ -435,10 +435,13 @@ void BaseTile::paintBitmap()
         if (!m_dirtyArea[m_currentDirtyAreaIndex].isEmpty())
             m_dirty = true;
 
-        XLOG("painted tile %p (%d, %d), dirty=%d", this, x, y, m_dirty);
+        XLOG("painted tile %p (%d, %d), texture %p, dirty=%d", this, x, y, texture, m_dirty);
 
-        if (!m_dirty)
-            m_isSwapNeeded = true;
+        if (!m_dirty) {
+            // swap textures, but WAIT until the next draw call (since we need
+            // to let GLWebViewState blit them at the beginning of drawGL)
+            m_swapDrawCount = TilesManager::instance()->getDrawGLCount() + 1;
+        }
     }
 
     m_atomicSync.unlock();
@@ -459,7 +462,7 @@ void BaseTile::discardTextures() {
 
 bool BaseTile::swapTexturesIfNeeded() {
     android::AutoMutex lock(m_atomicSync);
-    if (m_isSwapNeeded) {
+    if (m_swapDrawCount && TilesManager::instance()->getDrawGLCount() >= m_swapDrawCount) {
         // discard old texture and swap the new one in its place
         if (m_frontTexture)
             m_frontTexture->release(this);
@@ -467,7 +470,7 @@ bool BaseTile::swapTexturesIfNeeded() {
         XLOG("%p's frontTexture was %p, now becoming %p", this, m_frontTexture, m_backTexture);
         m_frontTexture = m_backTexture;
         m_backTexture = 0;
-        m_isSwapNeeded = false;
+        m_swapDrawCount = 0;
         XLOG("display texture for %d, %d front is now %p, texture is %p",
              m_x, m_y, m_frontTexture, m_backTexture);
         return true;
diff --git a/Source/WebCore/platform/graphics/android/BaseTile.h b/Source/WebCore/platform/graphics/android/BaseTile.h
index 4c9650f..734a3c8 100644
--- a/Source/WebCore/platform/graphics/android/BaseTile.h
+++ b/Source/WebCore/platform/graphics/android/BaseTile.h
@@ -148,7 +148,14 @@ private:
     BaseRenderer* m_renderer;
 
     bool m_isLayerTile;
-    bool m_isSwapNeeded;
+
+    // this is set when the back texture is finished painting and should be
+    // swapped to the front. it is set with the NEXT drawGL call (see
+    // TilesManager::m_drawGLCount) so that the textures may be blitted at the
+    // beginning of GLWebViewState::drawGL before they are swapped
+
+    // 4 steps for texture: paint -> blit -> swap -> draw
+    unsigned long long m_swapDrawCount;
 
     // the most recent GL draw before this tile was prepared. used for
     // prioritization and caching. tiles with old drawcounts and textures they
diff --git a/Source/WebCore/platform/graphics/android/BaseTileTexture.cpp b/Source/WebCore/platform/graphics/android/BaseTileTexture.cpp
index 8cc67b9..f049b6f 100644
--- a/Source/WebCore/platform/graphics/android/BaseTileTexture.cpp
+++ b/Source/WebCore/platform/graphics/android/BaseTileTexture.cpp
@@ -229,7 +229,6 @@ bool BaseTileTexture::release(TextureOwner* owner)
     // force readyFor to return false next call (even if texture reaquired by same tile)
     m_ownTextureTileInfo.m_x = -1;
     m_ownTextureTileInfo.m_y = -1;
-    m_ownTextureTileInfo.m_scale = 0;
     if (!m_busy) {
         m_owner = 0;
     } else {
diff --git a/Source/WebCore/platform/graphics/android/TilesManager.cpp b/Source/WebCore/platform/graphics/android/TilesManager.cpp
index bb8feb9..ee35ce2 100644
--- a/Source/WebCore/platform/graphics/android/TilesManager.cpp
+++ b/Source/WebCore/platform/graphics/android/TilesManager.cpp
@@ -100,7 +100,7 @@ TilesManager::TilesManager()
     , m_showVisualIndicator(false)
     , m_invertedScreen(false)
     , m_invertedScreenSwitch(false)
-    , m_drawGLCount(0)
+    , m_drawGLCount(1)
 {
     XLOG("TilesManager ctor");
     m_textures.reserveCapacity(MAX_TEXTURE_ALLOCATION);
@@ -268,9 +268,10 @@ BaseTileTexture* TilesManager::getAvailableTexture(BaseTile* owner)
 
     // The heuristic for selecting a texture is as follows:
     //  1. If a tile isn't owned, break with that one
-    //  2. If we find a tile in the same page with a different scale,
+    //  2. Don't let tiles acquire their front textures
+    //  3. If we find a tile in the same page with a different scale,
     //         it's old and not visible. Break with that one
-    //  3. Otherwise, use the least recently prepared tile, but ignoring tiles
+    //  4. Otherwise, use the least recently prepared tile, but ignoring tiles
     //         drawn in the last frame to avoid flickering
 
     BaseTileTexture* farthestTexture = 0;
@@ -284,6 +285,11 @@ BaseTileTexture* TilesManager::getAvailableTexture(BaseTile* owner)
             break;
         }
 
+        // Don't let a tile acquire its own front texture, as the acquisition
+        // logic doesn't handle that
+        if (currentOwner == owner)
+            continue;
+
         if (currentOwner->page() == owner->page() && texture->scale() != owner->scale()) {
             // if we render the back page with one scale, then another while
             // still zooming, we recycle the tiles with the old scale instead of
@@ -300,12 +306,13 @@ BaseTileTexture* TilesManager::getAvailableTexture(BaseTile* owner)
     }
 
     if (farthestTexture) {
-        TextureOwner* previousOwner = farthestTexture->owner();
+        BaseTile* previousOwner = static_cast<BaseTile*>(farthestTexture->owner());
         if (farthestTexture->acquire(owner)) {
             if (previousOwner) {
-                XLOG("%s texture %p stolen from tile %d, %d, drawCount was %llu",
+                XLOG("%s texture %p stolen from tile %d, %d, drawCount was %llu (current is %llu)",
                      owner->isLayerTile() ? "LAYER" : "BASE",
-                     farthestTexture, owner->x(), owner->y(), oldestDrawCount);
+                     farthestTexture, previousOwner->x(), previousOwner->y(),
+                     oldestDrawCount, getDrawGLCount());
             }
 
             availableTexturePool->remove(availableTexturePool->find(farthestTexture));
@@ -313,7 +320,8 @@ BaseTileTexture* TilesManager::getAvailableTexture(BaseTile* owner)
         }
     }
 
-    XLOG("Couldn't find an available texture for tile %x (%d, %d) out of %d available!!!",
+    XLOG("Couldn't find an available texture for %s tile %x (%d, %d) out of %d available",
+          owner->isLayerTile() ? "LAYER" : "BASE",
           owner, owner->x(), owner->y(), max);
 #ifdef DEBUG
     printTextures();