Add m-esr52 at 52.6.0

1 files changed, 1430 insertions, 0 deletions

diff --git a/gfx/layers/client/TiledContentClient.cpp b/gfx/layers/client/TiledContentClient.cpp
new file mode 100644
index 000000000..c5677a8a3
--- /dev/null
+++ b/gfx/layers/client/TiledContentClient.cpp
@@ -0,0 +1,1430 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/layers/TiledContentClient.h"
+#include <math.h>                       // for ceil, ceilf, floor
+#include <algorithm>
+#include "ClientTiledPaintedLayer.h"     // for ClientTiledPaintedLayer
+#include "GeckoProfiler.h"              // for PROFILER_LABEL
+#include "ClientLayerManager.h"         // for ClientLayerManager
+#include "gfxContext.h"                 // for gfxContext, etc
+#include "gfxPlatform.h"                // for gfxPlatform
+#include "gfxPrefs.h"                   // for gfxPrefs
+#include "gfxRect.h"                    // for gfxRect
+#include "mozilla/MathAlgorithms.h"     // for Abs
+#include "mozilla/gfx/Point.h"          // for IntSize
+#include "mozilla/gfx/Rect.h"           // for Rect
+#include "mozilla/gfx/Tools.h"          // for BytesPerPixel
+#include "mozilla/layers/CompositableForwarder.h"
+#include "mozilla/layers/CompositorBridgeChild.h" // for CompositorBridgeChild
+#include "mozilla/layers/LayerMetricsWrapper.h"
+#include "mozilla/layers/ShadowLayers.h"  // for ShadowLayerForwarder
+#include "TextureClientPool.h"
+#include "nsDebug.h"                    // for NS_ASSERTION
+#include "nsISupportsImpl.h"            // for gfxContext::AddRef, etc
+#include "nsExpirationTracker.h"        // for nsExpirationTracker
+#include "nsMathUtils.h"               // for NS_lroundf
+#include "LayersLogging.h"
+#include "UnitTransforms.h"             // for TransformTo
+#include "mozilla/UniquePtr.h"
+
+// This is the minimum area that we deem reasonable to copy from the front buffer to the
+// back buffer on tile updates. If the valid region is smaller than this, we just
+// redraw it and save on the copy (and requisite surface-locking involved).
+#define MINIMUM_TILE_COPY_AREA (1.f/16.f)
+
+#ifdef GFX_TILEDLAYER_DEBUG_OVERLAY
+#include "cairo.h"
+#include <sstream>
+using mozilla::layers::Layer;
+static void DrawDebugOverlay(mozilla::gfx::DrawTarget* dt, int x, int y, int width, int height)
+{
+  gfxContext c(dt);
+
+  // Draw border
+  c.NewPath();
+  c.SetDeviceColor(Color(0.f, 0.f, 0.f));
+  c.Rectangle(gfxRect(0, 0, width, height));
+  c.Stroke();
+
+  // Build tile description
+  std::stringstream ss;
+  ss << x << ", " << y;
+
+  // Draw text using cairo toy text API
+  // XXX: this drawing will silently fail if |dt| doesn't have a Cairo backend
+  cairo_t* cr = gfxFont::RefCairo(dt);
+  cairo_set_font_size(cr, 25);
+  cairo_text_extents_t extents;
+  cairo_text_extents(cr, ss.str().c_str(), &extents);
+
+  int textWidth = extents.width + 6;
+
+  c.NewPath();
+  c.SetDeviceColor(Color(0.f, 0.f, 0.f));
+  c.Rectangle(gfxRect(gfxPoint(2,2),gfxSize(textWidth, 30)));
+  c.Fill();
+
+  c.NewPath();
+  c.SetDeviceColor(Color(1.0, 0.0, 0.0));
+  c.Rectangle(gfxRect(gfxPoint(2,2),gfxSize(textWidth, 30)));
+  c.Stroke();
+
+  c.NewPath();
+  cairo_move_to(cr, 4, 28);
+  cairo_show_text(cr, ss.str().c_str());
+
+}
+
+#endif
+
+namespace mozilla {
+
+using namespace gfx;
+
+namespace layers {
+
+
+MultiTiledContentClient::MultiTiledContentClient(ClientTiledPaintedLayer& aPaintedLayer,
+                                                 ClientLayerManager* aManager)
+  : TiledContentClient(aManager, "Multi")
+  , mTiledBuffer(aPaintedLayer, *this, aManager, &mSharedFrameMetricsHelper)
+  , mLowPrecisionTiledBuffer(aPaintedLayer, *this, aManager, &mSharedFrameMetricsHelper)
+{
+  MOZ_COUNT_CTOR(MultiTiledContentClient);
+  mLowPrecisionTiledBuffer.SetResolution(gfxPrefs::LowPrecisionResolution());
+  mHasLowPrecision = gfxPrefs::UseLowPrecisionBuffer();
+}
+
+void
+MultiTiledContentClient::ClearCachedResources()
+{
+  CompositableClient::ClearCachedResources();
+  mTiledBuffer.DiscardBuffers();
+  mLowPrecisionTiledBuffer.DiscardBuffers();
+}
+
+void
+MultiTiledContentClient::UpdatedBuffer(TiledBufferType aType)
+{
+  ClientMultiTiledLayerBuffer* buffer = aType == LOW_PRECISION_TILED_BUFFER
+    ? &mLowPrecisionTiledBuffer
+    : &mTiledBuffer;
+
+  MOZ_ASSERT(aType != LOW_PRECISION_TILED_BUFFER || mHasLowPrecision);
+
+  mForwarder->UseTiledLayerBuffer(this, buffer->GetSurfaceDescriptorTiles());
+  buffer->ClearPaintedRegion();
+}
+
+SharedFrameMetricsHelper::SharedFrameMetricsHelper()
+  : mLastProgressiveUpdateWasLowPrecision(false)
+  , mProgressiveUpdateWasInDanger(false)
+{
+  MOZ_COUNT_CTOR(SharedFrameMetricsHelper);
+}
+
+SharedFrameMetricsHelper::~SharedFrameMetricsHelper()
+{
+  MOZ_COUNT_DTOR(SharedFrameMetricsHelper);
+}
+
+static inline bool
+FuzzyEquals(float a, float b) {
+  return (fabsf(a - b) < 1e-6);
+}
+
+static AsyncTransform
+ComputeViewTransform(const FrameMetrics& aContentMetrics, const FrameMetrics& aCompositorMetrics)
+{
+  // This is basically the same code as AsyncPanZoomController::GetCurrentAsyncTransform
+  // but with aContentMetrics used in place of mLastContentPaintMetrics, because they
+  // should be equivalent, modulo race conditions while transactions are inflight.
+
+  ParentLayerPoint translation = (aCompositorMetrics.GetScrollOffset() - aContentMetrics.GetScrollOffset())
+                               * aCompositorMetrics.GetZoom();
+  return AsyncTransform(aCompositorMetrics.GetAsyncZoom(), -translation);
+}
+
+bool
+SharedFrameMetricsHelper::UpdateFromCompositorFrameMetrics(
+    const LayerMetricsWrapper& aLayer,
+    bool aHasPendingNewThebesContent,
+    bool aLowPrecision,
+    AsyncTransform& aViewTransform)
+{
+  MOZ_ASSERT(aLayer);
+
+  CompositorBridgeChild* compositor = nullptr;
+  if (aLayer.Manager() &&
+      aLayer.Manager()->AsClientLayerManager()) {
+    compositor = aLayer.Manager()->AsClientLayerManager()->GetCompositorBridgeChild();
+  }
+
+  if (!compositor) {
+    return false;
+  }
+
+  const FrameMetrics& contentMetrics = aLayer.Metrics();
+  FrameMetrics compositorMetrics;
+
+  if (!compositor->LookupCompositorFrameMetrics(contentMetrics.GetScrollId(),
+                                                compositorMetrics)) {
+    return false;
+  }
+
+  aViewTransform = ComputeViewTransform(contentMetrics, compositorMetrics);
+
+  // Reset the checkerboard risk flag when switching to low precision
+  // rendering.
+  if (aLowPrecision && !mLastProgressiveUpdateWasLowPrecision) {
+    // Skip low precision rendering until we're at risk of checkerboarding.
+    if (!mProgressiveUpdateWasInDanger) {
+      TILING_LOG("TILING: Aborting low-precision rendering because not at risk of checkerboarding\n");
+      return true;
+    }
+    mProgressiveUpdateWasInDanger = false;
+  }
+  mLastProgressiveUpdateWasLowPrecision = aLowPrecision;
+
+  // Always abort updates if the resolution has changed. There's no use
+  // in drawing at the incorrect resolution.
+  if (!FuzzyEquals(compositorMetrics.GetZoom().xScale, contentMetrics.GetZoom().xScale) ||
+      !FuzzyEquals(compositorMetrics.GetZoom().yScale, contentMetrics.GetZoom().yScale)) {
+    TILING_LOG("TILING: Aborting because resolution changed from %s to %s\n",
+        ToString(contentMetrics.GetZoom()).c_str(), ToString(compositorMetrics.GetZoom()).c_str());
+    return true;
+  }
+
+  // Never abort drawing if we can't be sure we've sent a more recent
+  // display-port. If we abort updating when we shouldn't, we can end up
+  // with blank regions on the screen and we open up the risk of entering
+  // an endless updating cycle.
+  if (fabsf(contentMetrics.GetScrollOffset().x - compositorMetrics.GetScrollOffset().x) <= 2 &&
+      fabsf(contentMetrics.GetScrollOffset().y - compositorMetrics.GetScrollOffset().y) <= 2 &&
+      fabsf(contentMetrics.GetDisplayPort().x - compositorMetrics.GetDisplayPort().x) <= 2 &&
+      fabsf(contentMetrics.GetDisplayPort().y - compositorMetrics.GetDisplayPort().y) <= 2 &&
+      fabsf(contentMetrics.GetDisplayPort().width - compositorMetrics.GetDisplayPort().width) <= 2 &&
+      fabsf(contentMetrics.GetDisplayPort().height - compositorMetrics.GetDisplayPort().height) <= 2) {
+    return false;
+  }
+
+  // When not a low precision pass and the page is in danger of checker boarding
+  // abort update.
+  if (!aLowPrecision && !mProgressiveUpdateWasInDanger) {
+    bool scrollUpdatePending = contentMetrics.GetScrollOffsetUpdated() &&
+        contentMetrics.GetScrollGeneration() != compositorMetrics.GetScrollGeneration();
+    // If scrollUpdatePending is true, then that means the content-side
+    // metrics has a new scroll offset that is going to be forced into the
+    // compositor but it hasn't gotten there yet.
+    // Even though right now comparing the metrics might indicate we're
+    // about to checkerboard (and that's true), the checkerboarding will
+    // disappear as soon as the new scroll offset update is processed
+    // on the compositor side. To avoid leaving things in a low-precision
+    // paint, we need to detect and handle this case (bug 1026756).
+    if (!scrollUpdatePending && AboutToCheckerboard(contentMetrics, compositorMetrics)) {
+      mProgressiveUpdateWasInDanger = true;
+      return true;
+    }
+  }
+
+  // Abort drawing stale low-precision content if there's a more recent
+  // display-port in the pipeline.
+  if (aLowPrecision && !aHasPendingNewThebesContent) {
+    TILING_LOG("TILING: Aborting low-precision because of new pending content\n");
+    return true;
+  }
+
+  return false;
+}
+
+bool
+SharedFrameMetricsHelper::AboutToCheckerboard(const FrameMetrics& aContentMetrics,
+                                              const FrameMetrics& aCompositorMetrics)
+{
+  // The size of the painted area is originally computed in layer pixels in layout, but then
+  // converted to app units and then back to CSS pixels before being put in the FrameMetrics.
+  // This process can introduce some rounding error, so we inflate the rect by one app unit
+  // to account for that.
+  CSSRect painted = (aContentMetrics.GetCriticalDisplayPort().IsEmpty()
+                      ? aContentMetrics.GetDisplayPort()
+                      : aContentMetrics.GetCriticalDisplayPort())
+                    + aContentMetrics.GetScrollOffset();
+  painted.Inflate(CSSMargin::FromAppUnits(nsMargin(1, 1, 1, 1)));
+
+  // Inflate the rect by the danger zone. See the description of the danger zone prefs
+  // in AsyncPanZoomController.cpp for an explanation of this.
+  CSSRect showing = CSSRect(aCompositorMetrics.GetScrollOffset(),
+                            aCompositorMetrics.CalculateBoundedCompositedSizeInCssPixels());
+  showing.Inflate(LayerSize(gfxPrefs::APZDangerZoneX(), gfxPrefs::APZDangerZoneY())
+                  / aCompositorMetrics.LayersPixelsPerCSSPixel());
+
+  // Clamp both rects to the scrollable rect, because having either of those
+  // exceed the scrollable rect doesn't make sense, and could lead to false
+  // positives.
+  painted = painted.Intersect(aContentMetrics.GetScrollableRect());
+  showing = showing.Intersect(aContentMetrics.GetScrollableRect());
+
+  if (!painted.Contains(showing)) {
+    TILING_LOG("TILING: About to checkerboard; content %s\n", Stringify(aContentMetrics).c_str());
+    TILING_LOG("TILING: About to checkerboard; painted %s\n", Stringify(painted).c_str());
+    TILING_LOG("TILING: About to checkerboard; compositor %s\n", Stringify(aCompositorMetrics).c_str());
+    TILING_LOG("TILING: About to checkerboard; showing %s\n", Stringify(showing).c_str());
+    return true;
+  }
+  return false;
+}
+
+ClientMultiTiledLayerBuffer::ClientMultiTiledLayerBuffer(ClientTiledPaintedLayer& aPaintedLayer,
+                                                         CompositableClient& aCompositableClient,
+                                                         ClientLayerManager* aManager,
+                                                         SharedFrameMetricsHelper* aHelper)
+  : ClientTiledLayerBuffer(aPaintedLayer, aCompositableClient)
+  , mManager(aManager)
+  , mCallback(nullptr)
+  , mCallbackData(nullptr)
+  , mSharedFrameMetricsHelper(aHelper)
+{
+}
+
+bool
+ClientTiledLayerBuffer::HasFormatChanged() const
+{
+  SurfaceMode mode;
+  gfxContentType content = GetContentType(&mode);
+  return content != mLastPaintContentType ||
+         mode != mLastPaintSurfaceMode;
+}
+
+
+gfxContentType
+ClientTiledLayerBuffer::GetContentType(SurfaceMode* aMode) const
+{
+  gfxContentType content =
+    mPaintedLayer.CanUseOpaqueSurface() ? gfxContentType::COLOR :
+                                          gfxContentType::COLOR_ALPHA;
+  SurfaceMode mode = mPaintedLayer.GetSurfaceMode();
+
+  if (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+#if defined(MOZ_GFX_OPTIMIZE_MOBILE)
+    mode = SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+#else
+    if (!mPaintedLayer.GetParent() ||
+        !mPaintedLayer.GetParent()->SupportsComponentAlphaChildren()) {
+      mode = SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+    } else {
+      content = gfxContentType::COLOR;
+    }
+#endif
+  } else if (mode == SurfaceMode::SURFACE_OPAQUE) {
+#if defined(MOZ_GFX_OPTIMIZE_MOBILE)
+    if (IsLowPrecision()) {
+      // If we're in low-res mode, drawing can sample from outside the visible
+      // region. Make sure that we only sample transparency if that happens.
+      mode = SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+      content = gfxContentType::COLOR_ALPHA;
+    }
+#else
+    if (mPaintedLayer.MayResample()) {
+      mode = SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+      content = gfxContentType::COLOR_ALPHA;
+    }
+#endif
+  }
+
+  if (aMode) {
+    *aMode = mode;
+  }
+  return content;
+}
+
+class TileExpiry final : public nsExpirationTracker<TileClient, 3>
+{
+  public:
+    TileExpiry() : nsExpirationTracker<TileClient, 3>(1000, "TileExpiry") {}
+
+    static void AddTile(TileClient* aTile)
+    {
+      if (!sTileExpiry) {
+        sTileExpiry = MakeUnique<TileExpiry>();
+      }
+
+      sTileExpiry->AddObject(aTile);
+    }
+
+    static void RemoveTile(TileClient* aTile)
+    {
+      MOZ_ASSERT(sTileExpiry);
+      sTileExpiry->RemoveObject(aTile);
+    }
+
+    static void Shutdown() {
+      sTileExpiry = nullptr;
+    }
+  private:
+    virtual void NotifyExpired(TileClient* aTile) override
+    {
+      aTile->DiscardBackBuffer();
+    }
+
+    static UniquePtr<TileExpiry> sTileExpiry;
+};
+UniquePtr<TileExpiry> TileExpiry::sTileExpiry;
+
+void ShutdownTileCache()
+{
+  TileExpiry::Shutdown();
+}
+
+void
+TileClient::PrivateProtector::Set(TileClient * const aContainer, RefPtr<TextureClient> aNewValue)
+{
+  if (mBuffer) {
+    TileExpiry::RemoveTile(aContainer);
+  }
+  mBuffer = aNewValue;
+  if (mBuffer) {
+    TileExpiry::AddTile(aContainer);
+  }
+}
+
+void
+TileClient::PrivateProtector::Set(TileClient * const aContainer, TextureClient* aNewValue)
+{
+  Set(aContainer, RefPtr<TextureClient>(aNewValue));
+}
+
+// Placeholder
+TileClient::TileClient()
+  : mWasPlaceholder(false)
+{
+}
+
+TileClient::~TileClient()
+{
+  if (mExpirationState.IsTracked()) {
+    MOZ_ASSERT(mBackBuffer);
+    TileExpiry::RemoveTile(this);
+  }
+}
+
+TileClient::TileClient(const TileClient& o)
+{
+  mBackBuffer.Set(this, o.mBackBuffer);
+  mBackBufferOnWhite = o.mBackBufferOnWhite;
+  mFrontBuffer = o.mFrontBuffer;
+  mFrontBufferOnWhite = o.mFrontBufferOnWhite;
+  mWasPlaceholder = o.mWasPlaceholder;
+  mUpdateRect = o.mUpdateRect;
+#ifdef GFX_TILEDLAYER_DEBUG_OVERLAY
+  mLastUpdate = o.mLastUpdate;
+#endif
+  mAllocator = o.mAllocator;
+  mInvalidFront = o.mInvalidFront;
+  mInvalidBack = o.mInvalidBack;
+}
+
+TileClient&
+TileClient::operator=(const TileClient& o)
+{
+  if (this == &o) return *this;
+  mBackBuffer.Set(this, o.mBackBuffer);
+  mBackBufferOnWhite = o.mBackBufferOnWhite;
+  mFrontBuffer = o.mFrontBuffer;
+  mFrontBufferOnWhite = o.mFrontBufferOnWhite;
+  mWasPlaceholder = o.mWasPlaceholder;
+  mUpdateRect = o.mUpdateRect;
+#ifdef GFX_TILEDLAYER_DEBUG_OVERLAY
+  mLastUpdate = o.mLastUpdate;
+#endif
+  mAllocator = o.mAllocator;
+  mInvalidFront = o.mInvalidFront;
+  mInvalidBack = o.mInvalidBack;
+  return *this;
+}
+
+void
+TileClient::Dump(std::stringstream& aStream)
+{
+  aStream << "TileClient(bb=" << (TextureClient*)mBackBuffer << " fb=" << mFrontBuffer.get();
+  if (mBackBufferOnWhite) {
+    aStream << " bbow=" << mBackBufferOnWhite.get();
+  }
+  if (mFrontBufferOnWhite) {
+    aStream << " fbow=" << mFrontBufferOnWhite.get();
+  }
+  aStream << ")";
+}
+
+void
+TileClient::Flip()
+{
+  RefPtr<TextureClient> frontBuffer = mFrontBuffer;
+  RefPtr<TextureClient> frontBufferOnWhite = mFrontBufferOnWhite;
+  mFrontBuffer = mBackBuffer;
+  mFrontBufferOnWhite = mBackBufferOnWhite;
+  mBackBuffer.Set(this, frontBuffer);
+  mBackBufferOnWhite = frontBufferOnWhite;
+  nsIntRegion invalidFront = mInvalidFront;
+  mInvalidFront = mInvalidBack;
+  mInvalidBack = invalidFront;
+}
+
+static bool
+CopyFrontToBack(TextureClient* aFront,
+                TextureClient* aBack,
+                const gfx::IntRect& aRectToCopy)
+{
+  TextureClientAutoLock frontLock(aFront, OpenMode::OPEN_READ);
+  if (!frontLock.Succeeded()) {
+    gfxCriticalError() << "[Tiling:Client] Failed to lock the tile's front buffer";
+    return false;
+  }
+
+  if (!aBack->Lock(OpenMode::OPEN_READ_WRITE)) {
+    gfxCriticalError() << "[Tiling:Client] Failed to lock the tile's back buffer";
+    return false;
+  }
+
+  gfx::IntPoint rectToCopyTopLeft = aRectToCopy.TopLeft();
+  aFront->CopyToTextureClient(aBack, &aRectToCopy, &rectToCopyTopLeft);
+  return true;
+}
+
+void
+TileClient::ValidateBackBufferFromFront(const nsIntRegion& aDirtyRegion,
+                                        nsIntRegion& aAddPaintedRegion)
+{
+  if (mBackBuffer && mFrontBuffer) {
+    gfx::IntSize tileSize = mFrontBuffer->GetSize();
+    const IntRect tileRect = IntRect(0, 0, tileSize.width, tileSize.height);
+
+    if (aDirtyRegion.Contains(tileRect)) {
+      // The dirty region means that we no longer need the front buffer, so
+      // discard it.
+      DiscardFrontBuffer();
+    } else {
+      // Region that needs copying.
+      nsIntRegion regionToCopy = mInvalidBack;
+
+      regionToCopy.Sub(regionToCopy, aDirtyRegion);
+
+      aAddPaintedRegion = regionToCopy;
+
+      if (regionToCopy.IsEmpty()) {
+        // Just redraw it all.
+        return;
+      }
+
+      // Copy the bounding rect of regionToCopy. As tiles are quite small, it
+      // is unlikely that we'd save much by copying each individual rect of the
+      // region, but we can reevaluate this if it becomes an issue.
+      const IntRect rectToCopy = regionToCopy.GetBounds();
+      gfx::IntRect gfxRectToCopy(rectToCopy.x, rectToCopy.y, rectToCopy.width, rectToCopy.height);
+      CopyFrontToBack(mFrontBuffer, mBackBuffer, gfxRectToCopy);
+
+      if (mBackBufferOnWhite) {
+        MOZ_ASSERT(mFrontBufferOnWhite);
+        CopyFrontToBack(mFrontBufferOnWhite, mBackBufferOnWhite, gfxRectToCopy);
+      }
+
+      mInvalidBack.SetEmpty();
+    }
+  }
+}
+
+void
+TileClient::DiscardFrontBuffer()
+{
+  if (mFrontBuffer) {
+    MOZ_ASSERT(mFrontBuffer->GetReadLock());
+
+    MOZ_ASSERT(mAllocator);
+    if (mAllocator) {
+      mAllocator->ReturnTextureClientDeferred(mFrontBuffer);
+      if (mFrontBufferOnWhite) {
+        mAllocator->ReturnTextureClientDeferred(mFrontBufferOnWhite);
+      }
+    }
+
+    if (mFrontBuffer->IsLocked()) {
+      mFrontBuffer->Unlock();
+    }
+    if (mFrontBufferOnWhite && mFrontBufferOnWhite->IsLocked()) {
+      mFrontBufferOnWhite->Unlock();
+    }
+    mFrontBuffer = nullptr;
+    mFrontBufferOnWhite = nullptr;
+  }
+}
+
+static void
+DiscardTexture(TextureClient* aTexture, TextureClientAllocator* aAllocator)
+{
+  MOZ_ASSERT(aAllocator);
+  if (aTexture && aAllocator) {
+    MOZ_ASSERT(aTexture->GetReadLock());
+    if (!aTexture->HasSynchronization() && aTexture->IsReadLocked()) {
+      // Our current back-buffer is still locked by the compositor. This can occur
+      // when the client is producing faster than the compositor can consume. In
+      // this case we just want to drop it and not return it to the pool.
+     aAllocator->ReportClientLost();
+    } else {
+      aAllocator->ReturnTextureClientDeferred(aTexture);
+    }
+    if (aTexture->IsLocked()) {
+      aTexture->Unlock();
+    }
+  }
+}
+
+void
+TileClient::DiscardBackBuffer()
+{
+  if (mBackBuffer) {
+    DiscardTexture(mBackBuffer, mAllocator);
+    mBackBuffer.Set(this, nullptr);
+    DiscardTexture(mBackBufferOnWhite, mAllocator);
+    mBackBufferOnWhite = nullptr;
+  }
+}
+
+static already_AddRefed<TextureClient>
+CreateBackBufferTexture(TextureClient* aCurrentTexture,
+                        CompositableClient& aCompositable,
+                        TextureClientAllocator* aAllocator)
+{
+  if (aCurrentTexture) {
+    // Our current back-buffer is still locked by the compositor. This can occur
+    // when the client is producing faster than the compositor can consume. In
+    // this case we just want to drop it and not return it to the pool.
+    aAllocator->ReportClientLost();
+  }
+
+  RefPtr<TextureClient> texture = aAllocator->GetTextureClient();
+
+  if (!texture) {
+    gfxCriticalError() << "[Tiling:Client] Failed to allocate a TextureClient";
+    return nullptr;
+  }
+
+  texture->EnableReadLock();
+
+  if (!aCompositable.AddTextureClient(texture)) {
+    gfxCriticalError() << "[Tiling:Client] Failed to connect a TextureClient";
+    return nullptr;
+  }
+
+  return texture.forget();
+}
+
+TextureClient*
+TileClient::GetBackBuffer(CompositableClient& aCompositable,
+                          const nsIntRegion& aDirtyRegion,
+                          gfxContentType aContent,
+                          SurfaceMode aMode,
+                          nsIntRegion& aAddPaintedRegion,
+                          RefPtr<TextureClient>* aBackBufferOnWhite)
+{
+  if (!mAllocator) {
+    gfxCriticalError() << "[TileClient] Missing TextureClientAllocator.";
+    return nullptr;
+  }
+  if (aMode != SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+    // It can happen that a component-alpha layer stops being on component alpha
+    // on the next frame, just drop the buffers on white if that happens.
+    if (mBackBufferOnWhite) {
+      mAllocator->ReportClientLost();
+      mBackBufferOnWhite = nullptr;
+    }
+    if (mFrontBufferOnWhite) {
+      mAllocator->ReportClientLost();
+      mFrontBufferOnWhite = nullptr;
+    }
+  }
+
+  // Try to re-use the front-buffer if possible
+  if (mFrontBuffer &&
+      mFrontBuffer->HasIntermediateBuffer() &&
+      !mFrontBuffer->IsReadLocked() &&
+      (aMode != SurfaceMode::SURFACE_COMPONENT_ALPHA || (
+        mFrontBufferOnWhite && !mFrontBufferOnWhite->IsReadLocked()))) {
+    // If we had a backbuffer we no longer care about it since we'll
+    // re-use the front buffer.
+    DiscardBackBuffer();
+    Flip();
+  } else {
+    if (!mBackBuffer || mBackBuffer->IsReadLocked()) {
+      mBackBuffer.Set(this,
+        CreateBackBufferTexture(mBackBuffer, aCompositable, mAllocator)
+      );
+      if (!mBackBuffer) {
+        DiscardBackBuffer();
+        DiscardFrontBuffer();
+        return nullptr;
+      }
+      mInvalidBack = IntRect(IntPoint(), mBackBuffer->GetSize());
+    }
+
+    if (aMode == SurfaceMode::SURFACE_COMPONENT_ALPHA
+        && (!mBackBufferOnWhite || mBackBufferOnWhite->IsReadLocked())) {
+      mBackBufferOnWhite = CreateBackBufferTexture(
+        mBackBufferOnWhite, aCompositable, mAllocator
+      );
+      if (!mBackBufferOnWhite) {
+        DiscardBackBuffer();
+        DiscardFrontBuffer();
+        return nullptr;
+      }
+      mInvalidBack = IntRect(IntPoint(), mBackBufferOnWhite->GetSize());
+    }
+
+    ValidateBackBufferFromFront(aDirtyRegion, aAddPaintedRegion);
+  }
+
+  if (!mBackBuffer->IsLocked()) {
+    if (!mBackBuffer->Lock(OpenMode::OPEN_READ_WRITE)) {
+      gfxCriticalError() << "[Tiling:Client] Failed to lock a tile (B)";
+      DiscardBackBuffer();
+      DiscardFrontBuffer();
+      return nullptr;
+    }
+  }
+
+  if (mBackBufferOnWhite && !mBackBufferOnWhite->IsLocked()) {
+    if (!mBackBufferOnWhite->Lock(OpenMode::OPEN_READ_WRITE)) {
+      gfxCriticalError() << "[Tiling:Client] Failed to lock a tile (W)";
+      DiscardBackBuffer();
+      DiscardFrontBuffer();
+      return nullptr;
+    }
+  }
+
+  *aBackBufferOnWhite = mBackBufferOnWhite;
+  return mBackBuffer;
+}
+
+TileDescriptor
+TileClient::GetTileDescriptor()
+{
+  if (IsPlaceholderTile()) {
+    mWasPlaceholder = true;
+    return PlaceholderTileDescriptor();
+  }
+  bool wasPlaceholder = mWasPlaceholder;
+  mWasPlaceholder = false;
+
+  ReadLockDescriptor lock;
+  mFrontBuffer->SerializeReadLock(lock);
+
+  ReadLockDescriptor lockOnWhite = null_t();
+  if (mFrontBufferOnWhite) {
+    mFrontBufferOnWhite->SerializeReadLock(lockOnWhite);
+  }
+
+  return TexturedTileDescriptor(nullptr, mFrontBuffer->GetIPDLActor(),
+                                mFrontBufferOnWhite ? MaybeTexture(mFrontBufferOnWhite->GetIPDLActor()) : MaybeTexture(null_t()),
+                                mUpdateRect,
+                                lock, lockOnWhite,
+                                wasPlaceholder);
+}
+
+void
+ClientMultiTiledLayerBuffer::DiscardBuffers()
+{
+  for (TileClient& tile : mRetainedTiles) {
+    tile.DiscardBuffers();
+  }
+}
+
+SurfaceDescriptorTiles
+ClientMultiTiledLayerBuffer::GetSurfaceDescriptorTiles()
+{
+  InfallibleTArray<TileDescriptor> tiles;
+
+  for (TileClient& tile : mRetainedTiles) {
+    TileDescriptor tileDesc = tile.GetTileDescriptor();
+    tiles.AppendElement(tileDesc);
+    // Reset the update rect
+    tile.mUpdateRect = IntRect();
+  }
+  return SurfaceDescriptorTiles(mValidRegion,
+                                tiles,
+                                mTileOrigin, mTileSize,
+                                mTiles.mFirst.x, mTiles.mFirst.y,
+                                mTiles.mSize.width, mTiles.mSize.height,
+                                mResolution, mFrameResolution.xScale,
+                                mFrameResolution.yScale,
+                                mWasLastPaintProgressive);
+}
+
+void
+ClientMultiTiledLayerBuffer::PaintThebes(const nsIntRegion& aNewValidRegion,
+                                         const nsIntRegion& aPaintRegion,
+                                         const nsIntRegion& aDirtyRegion,
+                                         LayerManager::DrawPaintedLayerCallback aCallback,
+                                         void* aCallbackData,
+                                         bool aIsProgressive)
+{
+  TILING_LOG("TILING %p: PaintThebes painting region %s\n", &mPaintedLayer, Stringify(aPaintRegion).c_str());
+  TILING_LOG("TILING %p: PaintThebes new valid region %s\n", &mPaintedLayer, Stringify(aNewValidRegion).c_str());
+
+  mCallback = aCallback;
+  mCallbackData = aCallbackData;
+  mWasLastPaintProgressive = aIsProgressive;
+
+#ifdef GFX_TILEDLAYER_PREF_WARNINGS
+  long start = PR_IntervalNow();
+#endif
+
+#ifdef GFX_TILEDLAYER_PREF_WARNINGS
+  if (PR_IntervalNow() - start > 30) {
+    const IntRect bounds = aPaintRegion.GetBounds();
+    printf_stderr("Time to draw %i: %i, %i, %i, %i\n", PR_IntervalNow() - start, bounds.x, bounds.y, bounds.width, bounds.height);
+    if (aPaintRegion.IsComplex()) {
+      printf_stderr("Complex region\n");
+      for (auto iter = aPaintRegion.RectIter(); !iter.Done(); iter.Next()) {
+        const IntRect& rect = iter.Get();
+        printf_stderr(" rect %i, %i, %i, %i\n",
+                      rect.x, rect.y, rect.width, rect.height);
+      }
+    }
+  }
+  start = PR_IntervalNow();
+#endif
+
+  PROFILER_LABEL("ClientMultiTiledLayerBuffer", "PaintThebesUpdate",
+    js::ProfileEntry::Category::GRAPHICS);
+
+  mNewValidRegion = aNewValidRegion;
+  Update(aNewValidRegion, aPaintRegion, aDirtyRegion);
+
+#ifdef GFX_TILEDLAYER_PREF_WARNINGS
+  if (PR_IntervalNow() - start > 10) {
+    const IntRect bounds = aPaintRegion.GetBounds();
+    printf_stderr("Time to tile %i: %i, %i, %i, %i\n", PR_IntervalNow() - start, bounds.x, bounds.y, bounds.width, bounds.height);
+  }
+#endif
+
+  mLastPaintContentType = GetContentType(&mLastPaintSurfaceMode);
+  mCallback = nullptr;
+  mCallbackData = nullptr;
+}
+
+void PadDrawTargetOutFromRegion(RefPtr<DrawTarget> drawTarget, nsIntRegion &region)
+{
+  struct LockedBits {
+    uint8_t *data;
+    IntSize size;
+    int32_t stride;
+    SurfaceFormat format;
+    static int clamp(int x, int min, int max)
+    {
+      if (x < min)
+        x = min;
+      if (x > max)
+        x = max;
+      return x;
+    }
+
+    static void ensure_memcpy(uint8_t *dst, uint8_t *src, size_t n, uint8_t *bitmap, int stride, int height)
+    {
+        if (src + n > bitmap + stride*height) {
+            MOZ_CRASH("GFX: long src memcpy");
+        }
+        if (src < bitmap) {
+            MOZ_CRASH("GFX: short src memcpy");
+        }
+        if (dst + n > bitmap + stride*height) {
+            MOZ_CRASH("GFX: long dst mempcy");
+        }
+        if (dst < bitmap) {
+            MOZ_CRASH("GFX: short dst mempcy");
+        }
+    }
+
+    static void visitor(void *closure, VisitSide side, int x1, int y1, int x2, int y2) {
+      LockedBits *lb = static_cast<LockedBits*>(closure);
+      uint8_t *bitmap = lb->data;
+      const int bpp = gfx::BytesPerPixel(lb->format);
+      const int stride = lb->stride;
+      const int width = lb->size.width;
+      const int height = lb->size.height;
+
+      if (side == VisitSide::TOP) {
+        if (y1 > 0) {
+          x1 = clamp(x1, 0, width - 1);
+          x2 = clamp(x2, 0, width - 1);
+          ensure_memcpy(&bitmap[x1*bpp + (y1-1) * stride], &bitmap[x1*bpp + y1 * stride], (x2 - x1) * bpp, bitmap, stride, height);
+          memcpy(&bitmap[x1*bpp + (y1-1) * stride], &bitmap[x1*bpp + y1 * stride], (x2 - x1) * bpp);
+        }
+      } else if (side == VisitSide::BOTTOM) {
+        if (y1 < height) {
+          x1 = clamp(x1, 0, width - 1);
+          x2 = clamp(x2, 0, width - 1);
+          ensure_memcpy(&bitmap[x1*bpp + y1 * stride], &bitmap[x1*bpp + (y1-1) * stride], (x2 - x1) * bpp, bitmap, stride, height);
+          memcpy(&bitmap[x1*bpp + y1 * stride], &bitmap[x1*bpp + (y1-1) * stride], (x2 - x1) * bpp);
+        }
+      } else if (side == VisitSide::LEFT) {
+        if (x1 > 0) {
+          while (y1 != y2) {
+            memcpy(&bitmap[(x1-1)*bpp + y1 * stride], &bitmap[x1*bpp + y1*stride], bpp);
+            y1++;
+          }
+        }
+      } else if (side == VisitSide::RIGHT) {
+        if (x1 < width) {
+          while (y1 != y2) {
+            memcpy(&bitmap[x1*bpp + y1 * stride], &bitmap[(x1-1)*bpp + y1*stride], bpp);
+            y1++;
+          }
+        }
+      }
+
+    }
+  } lb;
+
+  if (drawTarget->LockBits(&lb.data, &lb.size, &lb.stride, &lb.format)) {
+    // we can only pad software targets so if we can't lock the bits don't pad
+    region.VisitEdges(lb.visitor, &lb);
+    drawTarget->ReleaseBits(lb.data);
+  }
+}
+
+void
+ClientTiledLayerBuffer::UnlockTile(TileClient& aTile)
+{
+  // We locked the back buffer, and flipped so we now need to unlock the front
+  if (aTile.mFrontBuffer && aTile.mFrontBuffer->IsLocked()) {
+    aTile.mFrontBuffer->Unlock();
+    aTile.mFrontBuffer->SyncWithObject(mCompositableClient.GetForwarder()->GetSyncObject());
+  }
+  if (aTile.mFrontBufferOnWhite && aTile.mFrontBufferOnWhite->IsLocked()) {
+    aTile.mFrontBufferOnWhite->Unlock();
+    aTile.mFrontBufferOnWhite->SyncWithObject(mCompositableClient.GetForwarder()->GetSyncObject());
+  }
+  if (aTile.mBackBuffer && aTile.mBackBuffer->IsLocked()) {
+    aTile.mBackBuffer->Unlock();
+  }
+  if (aTile.mBackBufferOnWhite && aTile.mBackBufferOnWhite->IsLocked()) {
+    aTile.mBackBufferOnWhite->Unlock();
+  }
+}
+
+void ClientMultiTiledLayerBuffer::Update(const nsIntRegion& newValidRegion,
+                                         const nsIntRegion& aPaintRegion,
+                                         const nsIntRegion& aDirtyRegion)
+{
+  const IntSize scaledTileSize = GetScaledTileSize();
+  const gfx::IntRect newBounds = newValidRegion.GetBounds();
+
+  const TilesPlacement oldTiles = mTiles;
+  const TilesPlacement newTiles(floor_div(newBounds.x, scaledTileSize.width),
+                          floor_div(newBounds.y, scaledTileSize.height),
+                          floor_div(GetTileStart(newBounds.x, scaledTileSize.width)
+                                    + newBounds.width, scaledTileSize.width) + 1,
+                          floor_div(GetTileStart(newBounds.y, scaledTileSize.height)
+                                    + newBounds.height, scaledTileSize.height) + 1);
+
+  const size_t oldTileCount = mRetainedTiles.Length();
+  const size_t newTileCount = newTiles.mSize.width * newTiles.mSize.height;
+
+  nsTArray<TileClient> oldRetainedTiles;
+  mRetainedTiles.SwapElements(oldRetainedTiles);
+  mRetainedTiles.SetLength(newTileCount);
+
+  for (size_t oldIndex = 0; oldIndex < oldTileCount; oldIndex++) {
+    const TileIntPoint tilePosition = oldTiles.TilePosition(oldIndex);
+    const size_t newIndex = newTiles.TileIndex(tilePosition);
+    // First, get the already existing tiles to the right place in the new array.
+    // Leave placeholders (default constructor) where there was no tile.
+    if (newTiles.HasTile(tilePosition)) {
+      mRetainedTiles[newIndex] = oldRetainedTiles[oldIndex];
+    } else {
+      // release tiles that we are not going to reuse before allocating new ones
+      // to avoid allocating unnecessarily.
+      oldRetainedTiles[oldIndex].DiscardBuffers();
+    }
+  }
+
+  oldRetainedTiles.Clear();
+
+  if (!aPaintRegion.IsEmpty()) {
+    for (size_t i = 0; i < newTileCount; ++i) {
+      const TileIntPoint tilePosition = newTiles.TilePosition(i);
+
+      IntPoint tileOffset = GetTileOffset(tilePosition);
+      nsIntRegion tileDrawRegion = IntRect(tileOffset, scaledTileSize);
+      tileDrawRegion.AndWith(aPaintRegion);
+
+      if (tileDrawRegion.IsEmpty()) {
+        continue;
+      }
+
+      TileClient& tile = mRetainedTiles[i];
+      if (!ValidateTile(tile, GetTileOffset(tilePosition), tileDrawRegion)) {
+        gfxCriticalError() << "ValidateTile failed";
+      }
+    }
+
+    if (mMoz2DTiles.size() > 0) {
+      gfx::TileSet tileset;
+      for (size_t i = 0; i < mMoz2DTiles.size(); ++i) {
+        mMoz2DTiles[i].mTileOrigin -= mTilingOrigin;
+      }
+      tileset.mTiles = &mMoz2DTiles[0];
+      tileset.mTileCount = mMoz2DTiles.size();
+      RefPtr<DrawTarget> drawTarget = gfx::Factory::CreateTiledDrawTarget(tileset);
+      if (!drawTarget || !drawTarget->IsValid()) {
+        gfxDevCrash(LogReason::InvalidContext) << "Invalid tiled draw target";
+        return;
+      }
+      drawTarget->SetTransform(Matrix());
+
+      RefPtr<gfxContext> ctx = gfxContext::CreateOrNull(drawTarget);
+      MOZ_ASSERT(ctx); // already checked the draw target above
+      ctx->SetMatrix(
+        ctx->CurrentMatrix().Scale(mResolution, mResolution).Translate(ThebesPoint(-mTilingOrigin)));
+
+      mCallback(&mPaintedLayer, ctx, aPaintRegion, aDirtyRegion,
+                DrawRegionClip::DRAW, nsIntRegion(), mCallbackData);
+      mMoz2DTiles.clear();
+      // Reset:
+      mTilingOrigin = IntPoint(std::numeric_limits<int32_t>::max(),
+                               std::numeric_limits<int32_t>::max());
+    }
+
+    bool edgePaddingEnabled = gfxPrefs::TileEdgePaddingEnabled();
+
+    for (uint32_t i = 0; i < mRetainedTiles.Length(); ++i) {
+      TileClient& tile = mRetainedTiles[i];
+
+      // Only worry about padding when not doing low-res because it simplifies
+      // the math and the artifacts won't be noticable
+      // Edge padding prevents sampling artifacts when compositing.
+      if (edgePaddingEnabled && mResolution == 1 &&
+          tile.mFrontBuffer && tile.mFrontBuffer->IsLocked()) {
+
+        const TileIntPoint tilePosition = newTiles.TilePosition(i);
+        IntPoint tileOffset = GetTileOffset(tilePosition);
+        // Strictly speakig we want the unscaled rect here, but it doesn't matter
+        // because we only run this code when the resolution is equal to 1.
+        IntRect tileRect = IntRect(tileOffset.x, tileOffset.y,
+                                   GetTileSize().width, GetTileSize().height);
+
+        nsIntRegion tileDrawRegion = IntRect(tileOffset, scaledTileSize);
+        tileDrawRegion.AndWith(aPaintRegion);
+
+        nsIntRegion tileValidRegion = mValidRegion;
+        tileValidRegion.OrWith(tileDrawRegion);
+
+        // We only need to pad out if the tile has area that's not valid
+        if (!tileValidRegion.Contains(tileRect)) {
+          tileValidRegion = tileValidRegion.Intersect(tileRect);
+          // translate the region into tile space and pad
+          tileValidRegion.MoveBy(-IntPoint(tileOffset.x, tileOffset.y));
+          RefPtr<DrawTarget> drawTarget = tile.mFrontBuffer->BorrowDrawTarget();
+          PadDrawTargetOutFromRegion(drawTarget, tileValidRegion);
+        }
+      }
+      UnlockTile(tile);
+    }
+  }
+
+  mTiles = newTiles;
+  mValidRegion = newValidRegion;
+  mPaintedRegion.OrWith(aPaintRegion);
+}
+
+bool
+ClientMultiTiledLayerBuffer::ValidateTile(TileClient& aTile,
+                                          const nsIntPoint& aTileOrigin,
+                                          const nsIntRegion& aDirtyRegion)
+{
+  PROFILER_LABEL("ClientMultiTiledLayerBuffer", "ValidateTile",
+    js::ProfileEntry::Category::GRAPHICS);
+
+#ifdef GFX_TILEDLAYER_PREF_WARNINGS
+  if (aDirtyRegion.IsComplex()) {
+    printf_stderr("Complex region\n");
+  }
+#endif
+
+  SurfaceMode mode;
+  gfxContentType content = GetContentType(&mode);
+
+  if (!aTile.mAllocator) {
+    aTile.SetTextureAllocator(mManager->GetCompositorBridgeChild()->GetTexturePool(
+      mManager->AsShadowForwarder(),
+      gfxPlatform::GetPlatform()->Optimal2DFormatForContent(content),
+      TextureFlags::DISALLOW_BIGIMAGE | TextureFlags::IMMEDIATE_UPLOAD));
+    MOZ_ASSERT(aTile.mAllocator);
+  }
+
+  nsIntRegion offsetScaledDirtyRegion = aDirtyRegion.MovedBy(-aTileOrigin);
+  offsetScaledDirtyRegion.ScaleRoundOut(mResolution, mResolution);
+
+  nsIntRegion extraPainted;
+  RefPtr<TextureClient> backBufferOnWhite;
+  RefPtr<TextureClient> backBuffer =
+    aTile.GetBackBuffer(mCompositableClient,
+                        offsetScaledDirtyRegion,
+                        content, mode,
+                        extraPainted,
+                        &backBufferOnWhite);
+
+  aTile.mUpdateRect = offsetScaledDirtyRegion.GetBounds().Union(extraPainted.GetBounds());
+
+  extraPainted.MoveBy(aTileOrigin);
+  extraPainted.And(extraPainted, mNewValidRegion);
+  mPaintedRegion.Or(mPaintedRegion, extraPainted);
+
+  if (!backBuffer) {
+    return false;
+  }
+
+  gfx::Tile moz2DTile;
+  RefPtr<DrawTarget> dt = backBuffer->BorrowDrawTarget();
+  RefPtr<DrawTarget> dtOnWhite;
+  if (backBufferOnWhite) {
+    dtOnWhite = backBufferOnWhite->BorrowDrawTarget();
+    moz2DTile.mDrawTarget = Factory::CreateDualDrawTarget(dt, dtOnWhite);
+  } else {
+    moz2DTile.mDrawTarget = dt;
+  }
+  moz2DTile.mTileOrigin = gfx::IntPoint(aTileOrigin.x, aTileOrigin.y);
+  if (!dt || (backBufferOnWhite && !dtOnWhite)) {
+    aTile.DiscardBuffers();
+    return false;
+  }
+
+  mMoz2DTiles.push_back(moz2DTile);
+  mTilingOrigin.x = std::min(mTilingOrigin.x, moz2DTile.mTileOrigin.x);
+  mTilingOrigin.y = std::min(mTilingOrigin.y, moz2DTile.mTileOrigin.y);
+
+  for (auto iter = aDirtyRegion.RectIter(); !iter.Done(); iter.Next()) {
+    const IntRect& dirtyRect = iter.Get();
+    gfx::Rect drawRect(dirtyRect.x - aTileOrigin.x,
+                       dirtyRect.y - aTileOrigin.y,
+                       dirtyRect.width,
+                       dirtyRect.height);
+    drawRect.Scale(mResolution);
+
+    // Mark the newly updated area as invalid in the front buffer
+    aTile.mInvalidFront.Or(aTile.mInvalidFront, IntRect::RoundOut(drawRect));
+
+    if (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+      dt->FillRect(drawRect, ColorPattern(Color(0.0, 0.0, 0.0, 1.0)));
+      dtOnWhite->FillRect(drawRect, ColorPattern(Color(1.0, 1.0, 1.0, 1.0)));
+    } else if (content == gfxContentType::COLOR_ALPHA) {
+      dt->ClearRect(drawRect);
+    }
+  }
+
+  // The new buffer is now validated, remove the dirty region from it.
+  aTile.mInvalidBack.SubOut(offsetScaledDirtyRegion);
+
+  aTile.Flip();
+
+  return true;
+}
+
+/**
+ * This function takes the transform stored in aTransformToCompBounds
+ * (which was generated in GetTransformToAncestorsParentLayer), and
+ * modifies it with the ViewTransform from the compositor side so that
+ * it reflects what the compositor is actually rendering. This operation
+ * basically adds in the layer's async transform.
+ * This function then returns the scroll ancestor's composition bounds,
+ * transformed into the painted layer's LayerPixel coordinates, accounting
+ * for the compositor state.
+ */
+static Maybe<LayerRect>
+GetCompositorSideCompositionBounds(const LayerMetricsWrapper& aScrollAncestor,
+                                   const LayerToParentLayerMatrix4x4& aTransformToCompBounds,
+                                   const AsyncTransform& aAPZTransform,
+                                   const LayerRect& aClip)
+{
+  LayerToParentLayerMatrix4x4 transform = aTransformToCompBounds *
+      AsyncTransformComponentMatrix(aAPZTransform);
+
+  return UntransformBy(transform.Inverse(),
+    aScrollAncestor.Metrics().GetCompositionBounds(), aClip);
+}
+
+bool
+ClientMultiTiledLayerBuffer::ComputeProgressiveUpdateRegion(const nsIntRegion& aInvalidRegion,
+                                                            const nsIntRegion& aOldValidRegion,
+                                                            nsIntRegion& aRegionToPaint,
+                                                            BasicTiledLayerPaintData* aPaintData,
+                                                            bool aIsRepeated)
+{
+  aRegionToPaint = aInvalidRegion;
+
+  // If the composition bounds rect is empty, we can't make any sensible
+  // decision about how to update coherently. In this case, just update
+  // everything in one transaction.
+  if (aPaintData->mCompositionBounds.IsEmpty()) {
+    aPaintData->mPaintFinished = true;
+    return false;
+  }
+
+  // If this is a low precision buffer, we force progressive updates. The
+  // assumption is that the contents is less important, so visual coherency
+  // is lower priority than speed.
+  bool drawingLowPrecision = IsLowPrecision();
+
+  // Find out if we have any non-stale content to update.
+  nsIntRegion staleRegion;
+  staleRegion.And(aInvalidRegion, aOldValidRegion);
+
+  TILING_LOG("TILING %p: Progressive update stale region %s\n", &mPaintedLayer, Stringify(staleRegion).c_str());
+
+  LayerMetricsWrapper scrollAncestor;
+  mPaintedLayer.GetAncestorLayers(&scrollAncestor, nullptr, nullptr);
+
+  // Find out the current view transform to determine which tiles to draw
+  // first, and see if we should just abort this paint. Aborting is usually
+  // caused by there being an incoming, more relevant paint.
+  AsyncTransform viewTransform;
+  MOZ_ASSERT(mSharedFrameMetricsHelper);
+
+  bool abortPaint =
+    mSharedFrameMetricsHelper->UpdateFromCompositorFrameMetrics(
+      scrollAncestor,
+      !staleRegion.Contains(aInvalidRegion),
+      drawingLowPrecision,
+      viewTransform);
+
+  TILING_LOG("TILING %p: Progressive update view transform %s zoom %f abort %d\n",
+      &mPaintedLayer, ToString(viewTransform.mTranslation).c_str(), viewTransform.mScale.scale, abortPaint);
+
+  if (abortPaint) {
+    // We ignore if front-end wants to abort if this is the first,
+    // non-low-precision paint, as in that situation, we're about to override
+    // front-end's page/viewport metrics.
+    if (!aPaintData->mFirstPaint || drawingLowPrecision) {
+      PROFILER_LABEL("ClientMultiTiledLayerBuffer", "ComputeProgressiveUpdateRegion",
+        js::ProfileEntry::Category::GRAPHICS);
+
+      aRegionToPaint.SetEmpty();
+      return aIsRepeated;
+    }
+  }
+
+  Maybe<LayerRect> transformedCompositionBounds =
+    GetCompositorSideCompositionBounds(scrollAncestor,
+                                       aPaintData->mTransformToCompBounds,
+                                       viewTransform,
+                                       ViewAs<LayerPixel>(Rect(mPaintedLayer.GetLayerBounds())));
+
+  if (!transformedCompositionBounds) {
+    aPaintData->mPaintFinished = true;
+    return false;
+  }
+
+  TILING_LOG("TILING %p: Progressive update transformed compositor bounds %s\n", &mPaintedLayer, Stringify(*transformedCompositionBounds).c_str());
+
+  // Compute a "coherent update rect" that we should paint all at once in a
+  // single transaction. This is to avoid rendering glitches on animated
+  // page content, and when layers change size/shape.
+  // On Fennec uploads are more expensive because we're not using gralloc, so
+  // we use a coherent update rect that is intersected with the screen at the
+  // time of issuing the draw command. This will paint faster but also potentially
+  // make the progressive paint more visible to the user while scrolling.
+  // On B2G uploads are cheaper and we value coherency more, especially outside
+  // the browser, so we always use the entire user-visible area.
+  IntRect coherentUpdateRect(RoundedOut(
+#ifdef MOZ_WIDGET_ANDROID
+    transformedCompositionBounds->Intersect(aPaintData->mCompositionBounds)
+#else
+    *transformedCompositionBounds
+#endif
+  ).ToUnknownRect());
+
+  TILING_LOG("TILING %p: Progressive update final coherency rect %s\n", &mPaintedLayer, Stringify(coherentUpdateRect).c_str());
+
+  aRegionToPaint.And(aInvalidRegion, coherentUpdateRect);
+  aRegionToPaint.Or(aRegionToPaint, staleRegion);
+  bool drawingStale = !aRegionToPaint.IsEmpty();
+  if (!drawingStale) {
+    aRegionToPaint = aInvalidRegion;
+  }
+
+  // Prioritise tiles that are currently visible on the screen.
+  bool paintingVisible = false;
+  if (aRegionToPaint.Intersects(coherentUpdateRect)) {
+    aRegionToPaint.And(aRegionToPaint, coherentUpdateRect);
+    paintingVisible = true;
+  }
+
+  TILING_LOG("TILING %p: Progressive update final paint region %s\n", &mPaintedLayer, Stringify(aRegionToPaint).c_str());
+
+  // Paint area that's visible and overlaps previously valid content to avoid
+  // visible glitches in animated elements, such as gifs.
+  bool paintInSingleTransaction = paintingVisible && (drawingStale || aPaintData->mFirstPaint);
+
+  TILING_LOG("TILING %p: paintingVisible %d drawingStale %d firstPaint %d singleTransaction %d\n",
+    &mPaintedLayer, paintingVisible, drawingStale, aPaintData->mFirstPaint, paintInSingleTransaction);
+
+  // The following code decides what order to draw tiles in, based on the
+  // current scroll direction of the primary scrollable layer.
+  NS_ASSERTION(!aRegionToPaint.IsEmpty(), "Unexpectedly empty paint region!");
+  IntRect paintBounds = aRegionToPaint.GetBounds();
+
+  int startX, incX, startY, incY;
+  gfx::IntSize scaledTileSize = GetScaledTileSize();
+  if (aPaintData->mScrollOffset.x >= aPaintData->mLastScrollOffset.x) {
+    startX = RoundDownToTileEdge(paintBounds.x, scaledTileSize.width);
+    incX = scaledTileSize.width;
+  } else {
+    startX = RoundDownToTileEdge(paintBounds.XMost() - 1, scaledTileSize.width);
+    incX = -scaledTileSize.width;
+  }
+
+  if (aPaintData->mScrollOffset.y >= aPaintData->mLastScrollOffset.y) {
+    startY = RoundDownToTileEdge(paintBounds.y, scaledTileSize.height);
+    incY = scaledTileSize.height;
+  } else {
+    startY = RoundDownToTileEdge(paintBounds.YMost() - 1, scaledTileSize.height);
+    incY = -scaledTileSize.height;
+  }
+
+  // Find a tile to draw.
+  IntRect tileBounds(startX, startY, scaledTileSize.width, scaledTileSize.height);
+  int32_t scrollDiffX = aPaintData->mScrollOffset.x - aPaintData->mLastScrollOffset.x;
+  int32_t scrollDiffY = aPaintData->mScrollOffset.y - aPaintData->mLastScrollOffset.y;
+  // This loop will always terminate, as there is at least one tile area
+  // along the first/last row/column intersecting with regionToPaint, or its
+  // bounds would have been smaller.
+  while (true) {
+    aRegionToPaint.And(aInvalidRegion, tileBounds);
+    if (!aRegionToPaint.IsEmpty()) {
+      if (mResolution != 1) {
+        // Paint the entire tile for low-res. This is aimed to fixing low-res resampling
+        // and to avoid doing costly region accurate painting for a small area.
+        aRegionToPaint = tileBounds;
+      }
+      break;
+    }
+    if (Abs(scrollDiffY) >= Abs(scrollDiffX)) {
+      tileBounds.x += incX;
+    } else {
+      tileBounds.y += incY;
+    }
+  }
+
+  if (!aRegionToPaint.Contains(aInvalidRegion)) {
+    // The region needed to paint is larger then our progressive chunk size
+    // therefore update what we want to paint and ask for a new paint transaction.
+
+    // If we need to draw more than one tile to maintain coherency, make
+    // sure it happens in the same transaction by requesting this work be
+    // repeated immediately.
+    // If this is unnecessary, the remaining work will be done tile-by-tile in
+    // subsequent transactions. The caller code is responsible for scheduling
+    // the subsequent transactions as long as we don't set the mPaintFinished
+    // flag to true.
+    return (!drawingLowPrecision && paintInSingleTransaction);
+  }
+
+  // We're not repeating painting and we've not requested a repeat transaction,
+  // so the paint is finished. If there's still a separate low precision
+  // paint to do, it will get marked as unfinished later.
+  aPaintData->mPaintFinished = true;
+  return false;
+}
+
+bool
+ClientMultiTiledLayerBuffer::ProgressiveUpdate(nsIntRegion& aValidRegion,
+                                               nsIntRegion& aInvalidRegion,
+                                               const nsIntRegion& aOldValidRegion,
+                                               BasicTiledLayerPaintData* aPaintData,
+                                               LayerManager::DrawPaintedLayerCallback aCallback,
+                                               void* aCallbackData)
+{
+  TILING_LOG("TILING %p: Progressive update valid region %s\n", &mPaintedLayer, Stringify(aValidRegion).c_str());
+  TILING_LOG("TILING %p: Progressive update invalid region %s\n", &mPaintedLayer, Stringify(aInvalidRegion).c_str());
+  TILING_LOG("TILING %p: Progressive update old valid region %s\n", &mPaintedLayer, Stringify(aOldValidRegion).c_str());
+
+  bool repeat = false;
+  bool isBufferChanged = false;
+  do {
+    // Compute the region that should be updated. Repeat as many times as
+    // is required.
+    nsIntRegion regionToPaint;
+    repeat = ComputeProgressiveUpdateRegion(aInvalidRegion,
+                                            aOldValidRegion,
+                                            regionToPaint,
+                                            aPaintData,
+                                            repeat);
+
+    TILING_LOG("TILING %p: Progressive update computed paint region %s repeat %d\n", &mPaintedLayer, Stringify(regionToPaint).c_str(), repeat);
+
+    // There's no further work to be done.
+    if (regionToPaint.IsEmpty()) {
+      break;
+    }
+
+    isBufferChanged = true;
+
+    // Keep track of what we're about to refresh.
+    aValidRegion.Or(aValidRegion, regionToPaint);
+
+    // aValidRegion may have been altered by InvalidateRegion, but we still
+    // want to display stale content until it gets progressively updated.
+    // Create a region that includes stale content.
+    nsIntRegion validOrStale;
+    validOrStale.Or(aValidRegion, aOldValidRegion);
+
+    // Paint the computed region and subtract it from the invalid region.
+    PaintThebes(validOrStale, regionToPaint, aInvalidRegion,
+                aCallback, aCallbackData, true);
+    aInvalidRegion.Sub(aInvalidRegion, regionToPaint);
+  } while (repeat);
+
+  TILING_LOG("TILING %p: Progressive update final valid region %s buffer changed %d\n", &mPaintedLayer, Stringify(aValidRegion).c_str(), isBufferChanged);
+  TILING_LOG("TILING %p: Progressive update final invalid region %s\n", &mPaintedLayer, Stringify(aInvalidRegion).c_str());
+
+  // Return false if nothing has been drawn, or give what has been drawn
+  // to the shadow layer to upload.
+  return isBufferChanged;
+}
+
+void
+TiledContentClient::PrintInfo(std::stringstream& aStream, const char* aPrefix)
+{
+  aStream << aPrefix;
+  aStream << nsPrintfCString("%sTiledContentClient (0x%p)", mName, this).get();
+
+  if (profiler_feature_active("displaylistdump")) {
+    nsAutoCString pfx(aPrefix);
+    pfx += "  ";
+
+    Dump(aStream, pfx.get(), false);
+  }
+}
+
+void
+TiledContentClient::Dump(std::stringstream& aStream,
+                         const char* aPrefix,
+                         bool aDumpHtml,
+                         TextureDumpMode aCompress)
+{
+  GetTiledBuffer()->Dump(aStream, aPrefix, aDumpHtml, aCompress);
+}
+
+void
+BasicTiledLayerPaintData::ResetPaintData()
+{
+  mLowPrecisionPaintCount = 0;
+  mPaintFinished = false;
+  mHasTransformAnimation = false;
+  mCompositionBounds.SetEmpty();
+  mCriticalDisplayPort = Nothing();
+}
+
+} // namespace layers
+} // namespace mozilla