diff -r 000000000000 -r 6474c204b198 gfx/layers/RotatedBuffer.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/layers/RotatedBuffer.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,737 @@
+/* -*- 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 "RotatedBuffer.h"
+#include <sys/types.h>                  // for int32_t
+#include <algorithm>                    // for max
+#include "BasicImplData.h"              // for BasicImplData
+#include "BasicLayersImpl.h"            // for ToData
+#include "BufferUnrotate.h"             // for BufferUnrotate
+#include "GeckoProfiler.h"              // for PROFILER_LABEL
+#include "Layers.h"                     // for ThebesLayer, Layer, etc
+#include "gfxPlatform.h"                // for gfxPlatform
+#include "gfxPrefs.h"                   // for gfxPrefs
+#include "gfxUtils.h"                   // for gfxUtils
+#include "mozilla/ArrayUtils.h"         // for ArrayLength
+#include "mozilla/gfx/BasePoint.h"      // for BasePoint
+#include "mozilla/gfx/BaseRect.h"       // for BaseRect
+#include "mozilla/gfx/BaseSize.h"       // for BaseSize
+#include "mozilla/gfx/Matrix.h"         // for Matrix
+#include "mozilla/gfx/Point.h"          // for Point, IntPoint
+#include "mozilla/gfx/Rect.h"           // for Rect, IntRect
+#include "mozilla/gfx/Types.h"          // for ExtendMode::ExtendMode::CLAMP, etc
+#include "mozilla/layers/ShadowLayers.h"  // for ShadowableLayer
+#include "mozilla/layers/TextureClient.h"  // for TextureClient
+#include "nsSize.h"                     // for nsIntSize
+#include "gfx2DGlue.h"
+
+namespace mozilla {
+
+using namespace gfx;
+
+namespace layers {
+
+nsIntRect
+RotatedBuffer::GetQuadrantRectangle(XSide aXSide, YSide aYSide) const
+{
+  // quadrantTranslation is the amount we translate the top-left
+  // of the quadrant by to get coordinates relative to the layer
+  nsIntPoint quadrantTranslation = -mBufferRotation;
+  quadrantTranslation.x += aXSide == LEFT ? mBufferRect.width : 0;
+  quadrantTranslation.y += aYSide == TOP ? mBufferRect.height : 0;
+  return mBufferRect + quadrantTranslation;
+}
+
+Rect
+RotatedBuffer::GetSourceRectangle(XSide aXSide, YSide aYSide) const
+{
+  Rect result;
+  if (aXSide == LEFT) {
+    result.x = 0;
+    result.width = mBufferRotation.x;
+  } else {
+    result.x = mBufferRotation.x;
+    result.width = mBufferRect.width - mBufferRotation.x;
+  }
+  if (aYSide == TOP) {
+    result.y = 0;
+    result.height = mBufferRotation.y;
+  } else {
+    result.y = mBufferRotation.y;
+    result.height = mBufferRect.height - mBufferRotation.y;
+  }
+  return result;
+}
+
+/**
+ * @param aXSide LEFT means we draw from the left side of the buffer (which
+ * is drawn on the right side of mBufferRect). RIGHT means we draw from
+ * the right side of the buffer (which is drawn on the left side of
+ * mBufferRect).
+ * @param aYSide TOP means we draw from the top side of the buffer (which
+ * is drawn on the bottom side of mBufferRect). BOTTOM means we draw from
+ * the bottom side of the buffer (which is drawn on the top side of
+ * mBufferRect).
+ */
+void
+RotatedBuffer::DrawBufferQuadrant(gfx::DrawTarget* aTarget,
+                                  XSide aXSide, YSide aYSide,
+                                  ContextSource aSource,
+                                  float aOpacity,
+                                  gfx::CompositionOp aOperator,
+                                  gfx::SourceSurface* aMask,
+                                  const gfx::Matrix* aMaskTransform) const
+{
+  // The rectangle that we're going to fill. Basically we're going to
+  // render the buffer at mBufferRect + quadrantTranslation to get the
+  // pixels in the right place, but we're only going to paint within
+  // mBufferRect
+  nsIntRect quadrantRect = GetQuadrantRectangle(aXSide, aYSide);
+  nsIntRect fillRect;
+  if (!fillRect.IntersectRect(mBufferRect, quadrantRect))
+    return;
+
+  gfx::Point quadrantTranslation(quadrantRect.x, quadrantRect.y);
+
+  MOZ_ASSERT(aOperator == CompositionOp::OP_OVER || aOperator == CompositionOp::OP_SOURCE);
+  // direct2d is much slower when using OP_SOURCE so use OP_OVER and
+  // (maybe) a clear instead. Normally we need to draw in a single operation
+  // (to avoid flickering) but direct2d is ok since it defers rendering.
+  // We should try abstract this logic in a helper when we have other use
+  // cases.
+  if (aTarget->GetType() == BackendType::DIRECT2D && aOperator == CompositionOp::OP_SOURCE) {
+    aOperator = CompositionOp::OP_OVER;
+    if (mDTBuffer->GetFormat() == SurfaceFormat::B8G8R8A8) {
+      aTarget->ClearRect(ToRect(fillRect));
+    }
+  }
+
+  RefPtr<gfx::SourceSurface> snapshot;
+  if (aSource == BUFFER_BLACK) {
+    snapshot = mDTBuffer->Snapshot();
+  } else {
+    MOZ_ASSERT(aSource == BUFFER_WHITE);
+    snapshot = mDTBufferOnWhite->Snapshot();
+  }
+
+  if (aOperator == CompositionOp::OP_SOURCE) {
+    // OP_SOURCE is unbounded in Azure, and we really don't want that behaviour here.
+    // We also can't do a ClearRect+FillRect since we need the drawing to happen
+    // as an atomic operation (to prevent flickering).
+    aTarget->PushClipRect(gfx::Rect(fillRect.x, fillRect.y,
+                                    fillRect.width, fillRect.height));
+  }
+
+  if (aMask) {
+    Matrix oldTransform = aTarget->GetTransform();
+
+    // Transform from user -> buffer space.
+    Matrix transform;
+    transform.Translate(quadrantTranslation.x, quadrantTranslation.y);
+
+    Matrix inverseMask = *aMaskTransform;
+    inverseMask.Invert();
+
+    transform *= oldTransform;
+    transform *= inverseMask;
+
+#ifdef MOZ_GFX_OPTIMIZE_MOBILE
+    SurfacePattern source(snapshot, ExtendMode::CLAMP, transform, Filter::POINT);
+#else
+    SurfacePattern source(snapshot, ExtendMode::CLAMP, transform);
+#endif
+
+    aTarget->SetTransform(*aMaskTransform);
+    aTarget->MaskSurface(source, aMask, Point(0, 0), DrawOptions(aOpacity, aOperator));
+    aTarget->SetTransform(oldTransform);
+  } else {
+#ifdef MOZ_GFX_OPTIMIZE_MOBILE
+    DrawSurfaceOptions options(Filter::POINT);
+#else
+    DrawSurfaceOptions options;
+#endif
+    aTarget->DrawSurface(snapshot, ToRect(fillRect),
+                         GetSourceRectangle(aXSide, aYSide),
+                         options,
+                         DrawOptions(aOpacity, aOperator));
+  }
+
+  if (aOperator == CompositionOp::OP_SOURCE) {
+    aTarget->PopClip();
+  }
+}
+
+void
+RotatedBuffer::DrawBufferWithRotation(gfx::DrawTarget *aTarget, ContextSource aSource,
+                                      float aOpacity,
+                                      gfx::CompositionOp aOperator,
+                                      gfx::SourceSurface* aMask,
+                                      const gfx::Matrix* aMaskTransform) const
+{
+  PROFILER_LABEL("RotatedBuffer", "DrawBufferWithRotation");
+  // See above, in Azure Repeat should always be a safe, even faster choice
+  // though! Particularly on D2D Repeat should be a lot faster, need to look
+  // into that. TODO[Bas]
+  DrawBufferQuadrant(aTarget, LEFT, TOP, aSource, aOpacity, aOperator, aMask, aMaskTransform);
+  DrawBufferQuadrant(aTarget, RIGHT, TOP, aSource, aOpacity, aOperator, aMask, aMaskTransform);
+  DrawBufferQuadrant(aTarget, LEFT, BOTTOM, aSource, aOpacity, aOperator, aMask, aMaskTransform);
+  DrawBufferQuadrant(aTarget, RIGHT, BOTTOM, aSource, aOpacity, aOperator,aMask, aMaskTransform);
+}
+
+/* static */ bool
+RotatedContentBuffer::IsClippingCheap(DrawTarget* aTarget, const nsIntRegion& aRegion)
+{
+  // Assume clipping is cheap if the draw target just has an integer
+  // translation, and the visible region is simple.
+  return !aTarget->GetTransform().HasNonIntegerTranslation() &&
+         aRegion.GetNumRects() <= 1;
+}
+
+void
+RotatedContentBuffer::DrawTo(ThebesLayer* aLayer,
+                             DrawTarget* aTarget,
+                             float aOpacity,
+                             CompositionOp aOp,
+                             SourceSurface* aMask,
+                             const Matrix* aMaskTransform)
+{
+  if (!EnsureBuffer()) {
+    return;
+  }
+
+  bool clipped = false;
+
+  // If the entire buffer is valid, we can just draw the whole thing,
+  // no need to clip. But we'll still clip if clipping is cheap ---
+  // that might let us copy a smaller region of the buffer.
+  // Also clip to the visible region if we're told to.
+  if (!aLayer->GetValidRegion().Contains(BufferRect()) ||
+      (ToData(aLayer)->GetClipToVisibleRegion() &&
+       !aLayer->GetVisibleRegion().Contains(BufferRect())) ||
+      IsClippingCheap(aTarget, aLayer->GetEffectiveVisibleRegion())) {
+    // We don't want to draw invalid stuff, so we need to clip. Might as
+    // well clip to the smallest area possible --- the visible region.
+    // Bug 599189 if there is a non-integer-translation transform in aTarget,
+    // we might sample pixels outside GetEffectiveVisibleRegion(), which is wrong
+    // and may cause gray lines.
+    gfxUtils::ClipToRegionSnapped(aTarget, aLayer->GetEffectiveVisibleRegion());
+    clipped = true;
+  }
+
+  DrawBufferWithRotation(aTarget, BUFFER_BLACK, aOpacity, aOp, aMask, aMaskTransform);
+  if (clipped) {
+    aTarget->PopClip();
+  }
+}
+
+DrawTarget*
+RotatedContentBuffer::BorrowDrawTargetForQuadrantUpdate(const nsIntRect& aBounds,
+                                                        ContextSource aSource,
+                                                        DrawIterator* aIter)
+{
+  nsIntRect bounds = aBounds;
+  if (aIter) {
+    // If an iterator was provided, then BeginPaint must have been run with
+    // PAINT_CAN_DRAW_ROTATED, and the draw region might cover multiple quadrants.
+    // Iterate over each of them, and return an appropriate buffer each time we find
+    // one that intersects the draw region. The iterator mCount value tracks which
+    // quadrants we have considered across multiple calls to this function.
+    aIter->mDrawRegion.SetEmpty();
+    while (aIter->mCount < 4) {
+      nsIntRect quadrant = GetQuadrantRectangle((aIter->mCount & 1) ? LEFT : RIGHT,
+        (aIter->mCount & 2) ? TOP : BOTTOM);
+      aIter->mDrawRegion.And(aBounds, quadrant);
+      aIter->mCount++;
+      if (!aIter->mDrawRegion.IsEmpty()) {
+        break;
+      }
+    }
+    if (aIter->mDrawRegion.IsEmpty()) {
+      return nullptr;
+    }
+    bounds = aIter->mDrawRegion.GetBounds();
+  }
+
+  if (!EnsureBuffer()) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(!mLoanedDrawTarget, "draw target has been borrowed and not returned");
+  if (aSource == BUFFER_BOTH && HaveBufferOnWhite()) {
+    if (!EnsureBufferOnWhite()) {
+      return nullptr;
+    }
+    MOZ_ASSERT(mDTBuffer && mDTBufferOnWhite);
+    mLoanedDrawTarget = Factory::CreateDualDrawTarget(mDTBuffer, mDTBufferOnWhite);
+  } else if (aSource == BUFFER_WHITE) {
+    if (!EnsureBufferOnWhite()) {
+      return nullptr;
+    }
+    mLoanedDrawTarget = mDTBufferOnWhite;
+  } else {
+    // BUFFER_BLACK, or BUFFER_BOTH with a single buffer.
+    mLoanedDrawTarget = mDTBuffer;
+  }
+
+  // Figure out which quadrant to draw in
+  int32_t xBoundary = mBufferRect.XMost() - mBufferRotation.x;
+  int32_t yBoundary = mBufferRect.YMost() - mBufferRotation.y;
+  XSide sideX = bounds.XMost() <= xBoundary ? RIGHT : LEFT;
+  YSide sideY = bounds.YMost() <= yBoundary ? BOTTOM : TOP;
+  nsIntRect quadrantRect = GetQuadrantRectangle(sideX, sideY);
+  NS_ASSERTION(quadrantRect.Contains(bounds), "Messed up quadrants");
+
+  mLoanedTransform = mLoanedDrawTarget->GetTransform();
+  mLoanedTransform.Translate(-quadrantRect.x, -quadrantRect.y);
+  mLoanedDrawTarget->SetTransform(mLoanedTransform);
+  mLoanedTransform.Translate(quadrantRect.x, quadrantRect.y);
+
+  return mLoanedDrawTarget;
+}
+
+void
+BorrowDrawTarget::ReturnDrawTarget(gfx::DrawTarget*& aReturned)
+{
+  MOZ_ASSERT(aReturned == mLoanedDrawTarget);
+  mLoanedDrawTarget->SetTransform(mLoanedTransform);
+  mLoanedDrawTarget = nullptr;
+  aReturned = nullptr;
+}
+
+gfxContentType
+RotatedContentBuffer::BufferContentType()
+{
+  if (mBufferProvider || mDTBuffer) {
+    SurfaceFormat format;
+
+    if (mBufferProvider) {
+      format = mBufferProvider->GetFormat();
+    } else if (mDTBuffer) {
+      format = mDTBuffer->GetFormat();
+    }
+
+    return ContentForFormat(format);
+  }
+  return gfxContentType::SENTINEL;
+}
+
+bool
+RotatedContentBuffer::BufferSizeOkFor(const nsIntSize& aSize)
+{
+  return (aSize == mBufferRect.Size() ||
+          (SizedToVisibleBounds != mBufferSizePolicy &&
+           aSize < mBufferRect.Size()));
+}
+
+bool
+RotatedContentBuffer::EnsureBuffer()
+{
+  NS_ASSERTION(!mLoanedDrawTarget, "Loaned draw target must be returned");
+  if (!mDTBuffer) {
+    if (mBufferProvider) {
+      mDTBuffer = mBufferProvider->GetAsDrawTarget();
+    }
+  }
+
+  NS_WARN_IF_FALSE(mDTBuffer, "no buffer");
+  return !!mDTBuffer;
+}
+
+bool
+RotatedContentBuffer::EnsureBufferOnWhite()
+{
+  NS_ASSERTION(!mLoanedDrawTarget, "Loaned draw target must be returned");
+  if (!mDTBufferOnWhite) {
+    if (mBufferProviderOnWhite) {
+      mDTBufferOnWhite =
+        mBufferProviderOnWhite->GetAsDrawTarget();
+    }
+  }
+
+  NS_WARN_IF_FALSE(mDTBufferOnWhite, "no buffer");
+  return mDTBufferOnWhite;
+}
+
+bool
+RotatedContentBuffer::HaveBuffer() const
+{
+  return mDTBuffer || mBufferProvider;
+}
+
+bool
+RotatedContentBuffer::HaveBufferOnWhite() const
+{
+  return mDTBufferOnWhite || mBufferProviderOnWhite;
+}
+
+static void
+WrapRotationAxis(int32_t* aRotationPoint, int32_t aSize)
+{
+  if (*aRotationPoint < 0) {
+    *aRotationPoint += aSize;
+  } else if (*aRotationPoint >= aSize) {
+    *aRotationPoint -= aSize;
+  }
+}
+
+static nsIntRect
+ComputeBufferRect(const nsIntRect& aRequestedRect)
+{
+  nsIntRect rect(aRequestedRect);
+  // Set a minimum width to guarantee a minimum size of buffers we
+  // allocate (and work around problems on some platforms with smaller
+  // dimensions).  64 is the magic number needed to work around the
+  // rendering glitch, and guarantees image rows can be SIMD'd for
+  // even r5g6b5 surfaces pretty much everywhere.
+  rect.width = std::max(aRequestedRect.width, 64);
+#ifdef MOZ_WIDGET_GONK
+  // Set a minumum height to guarantee a minumum height of buffers we
+  // allocate. Some GL implementations fail to render gralloc textures
+  // with a height 9px-16px. It happens on Adreno 200. Adreno 320 does not
+  // have this problem. 32 is choosed as alignment of gralloc buffers.
+  // See Bug 873937.
+  // Increase the height only when the requested height is more than 0.
+  // See Bug 895976.
+  // XXX it might be better to disable it on the gpu that does not have
+  // the height problem.
+  if (rect.height > 0) {
+    rect.height = std::max(aRequestedRect.height, 32);
+  }
+#endif
+  return rect;
+}
+
+void
+RotatedContentBuffer::FlushBuffers()
+{
+  if (mDTBuffer) {
+    mDTBuffer->Flush();
+  }
+  if (mDTBufferOnWhite) {
+    mDTBufferOnWhite->Flush();
+  }
+}
+
+RotatedContentBuffer::PaintState
+RotatedContentBuffer::BeginPaint(ThebesLayer* aLayer,
+                                 uint32_t aFlags)
+{
+  PaintState result;
+  // We need to disable rotation if we're going to be resampled when
+  // drawing, because we might sample across the rotation boundary.
+  bool canHaveRotation = gfxPlatform::BufferRotationEnabled() &&
+                         !(aFlags & (PAINT_WILL_RESAMPLE | PAINT_NO_ROTATION));
+
+  nsIntRegion validRegion = aLayer->GetValidRegion();
+
+  bool canUseOpaqueSurface = aLayer->CanUseOpaqueSurface();
+  ContentType layerContentType =
+    canUseOpaqueSurface ? gfxContentType::COLOR :
+                          gfxContentType::COLOR_ALPHA;
+
+  SurfaceMode mode;
+  nsIntRegion neededRegion;
+  bool canReuseBuffer;
+  nsIntRect destBufferRect;
+
+  while (true) {
+    mode = aLayer->GetSurfaceMode();
+    neededRegion = aLayer->GetVisibleRegion();
+    canReuseBuffer = HaveBuffer() && BufferSizeOkFor(neededRegion.GetBounds().Size());
+    result.mContentType = layerContentType;
+
+    if (canReuseBuffer) {
+      if (mBufferRect.Contains(neededRegion.GetBounds())) {
+        // We don't need to adjust mBufferRect.
+        destBufferRect = mBufferRect;
+      } else if (neededRegion.GetBounds().Size() <= mBufferRect.Size()) {
+        // The buffer's big enough but doesn't contain everything that's
+        // going to be visible. We'll move it.
+        destBufferRect = nsIntRect(neededRegion.GetBounds().TopLeft(), mBufferRect.Size());
+      } else {
+        destBufferRect = neededRegion.GetBounds();
+      }
+    } else {
+      // We won't be reusing the buffer.  Compute a new rect.
+      destBufferRect = ComputeBufferRect(neededRegion.GetBounds());
+    }
+
+    if (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+#if defined(MOZ_GFX_OPTIMIZE_MOBILE) || defined(MOZ_WIDGET_GONK)
+      mode = SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+#else
+      if (!aLayer->GetParent() ||
+          !aLayer->GetParent()->SupportsComponentAlphaChildren() ||
+          !aLayer->Manager()->IsCompositingCheap() ||
+          !aLayer->AsShadowableLayer() ||
+          !aLayer->AsShadowableLayer()->HasShadow() ||
+          !gfxPrefs::ComponentAlphaEnabled()) {
+        mode = SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+      } else {
+        result.mContentType = gfxContentType::COLOR;
+      }
+#endif
+    }
+
+    if ((aFlags & PAINT_WILL_RESAMPLE) &&
+        (!neededRegion.GetBounds().IsEqualInterior(destBufferRect) ||
+         neededRegion.GetNumRects() > 1)) {
+      // The area we add to neededRegion might not be painted opaquely
+      if (mode == SurfaceMode::SURFACE_OPAQUE) {
+        result.mContentType = gfxContentType::COLOR_ALPHA;
+        mode = SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
+      }
+
+      // We need to validate the entire buffer, to make sure that only valid
+      // pixels are sampled
+      neededRegion = destBufferRect;
+    }
+
+    // If we have an existing buffer, but the content type has changed or we
+    // have transitioned into/out of component alpha, then we need to recreate it.
+    if (HaveBuffer() &&
+        (result.mContentType != BufferContentType() ||
+        (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) != HaveBufferOnWhite())) {
+
+      // We're effectively clearing the valid region, so we need to draw
+      // the entire needed region now.
+      result.mRegionToInvalidate = aLayer->GetValidRegion();
+      validRegion.SetEmpty();
+      Clear();
+      // Restart decision process with the cleared buffer. We can only go
+      // around the loop one more iteration, since mDTBuffer is null now.
+      continue;
+    }
+
+    break;
+  }
+
+  NS_ASSERTION(destBufferRect.Contains(neededRegion.GetBounds()),
+               "Destination rect doesn't contain what we need to paint");
+
+  result.mRegionToDraw.Sub(neededRegion, validRegion);
+
+  if (result.mRegionToDraw.IsEmpty())
+    return result;
+
+  // Do not modify result.mRegionToDraw or result.mContentType after this call.
+  // Do not modify mBufferRect, mBufferRotation, or mDidSelfCopy,
+  // or call CreateBuffer before this call.
+  FinalizeFrame(result.mRegionToDraw);
+
+  nsIntRect drawBounds = result.mRegionToDraw.GetBounds();
+  RefPtr<DrawTarget> destDTBuffer;
+  RefPtr<DrawTarget> destDTBufferOnWhite;
+  uint32_t bufferFlags = canHaveRotation ? ALLOW_REPEAT : 0;
+  if (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+    bufferFlags |= BUFFER_COMPONENT_ALPHA;
+  }
+  if (canReuseBuffer) {
+    if (!EnsureBuffer()) {
+      return result;
+    }
+    nsIntRect keepArea;
+    if (keepArea.IntersectRect(destBufferRect, mBufferRect)) {
+      // Set mBufferRotation so that the pixels currently in mDTBuffer
+      // will still be rendered in the right place when mBufferRect
+      // changes to destBufferRect.
+      nsIntPoint newRotation = mBufferRotation +
+        (destBufferRect.TopLeft() - mBufferRect.TopLeft());
+      WrapRotationAxis(&newRotation.x, mBufferRect.width);
+      WrapRotationAxis(&newRotation.y, mBufferRect.height);
+      NS_ASSERTION(nsIntRect(nsIntPoint(0,0), mBufferRect.Size()).Contains(newRotation),
+                   "newRotation out of bounds");
+      int32_t xBoundary = destBufferRect.XMost() - newRotation.x;
+      int32_t yBoundary = destBufferRect.YMost() - newRotation.y;
+      bool drawWrapsBuffer = (drawBounds.x < xBoundary && xBoundary < drawBounds.XMost()) ||
+                             (drawBounds.y < yBoundary && yBoundary < drawBounds.YMost());
+      if ((drawWrapsBuffer && !(aFlags & PAINT_CAN_DRAW_ROTATED)) ||
+          (newRotation != nsIntPoint(0,0) && !canHaveRotation)) {
+        // The stuff we need to redraw will wrap around an edge of the
+        // buffer (and the caller doesn't know how to support that), so
+        // move the pixels we can keep into a position that lets us
+        // redraw in just one quadrant.
+        if (mBufferRotation == nsIntPoint(0,0)) {
+          nsIntRect srcRect(nsIntPoint(0, 0), mBufferRect.Size());
+          nsIntPoint dest = mBufferRect.TopLeft() - destBufferRect.TopLeft();
+          MOZ_ASSERT(mDTBuffer);
+          mDTBuffer->CopyRect(IntRect(srcRect.x, srcRect.y, srcRect.width, srcRect.height),
+                              IntPoint(dest.x, dest.y));
+          if (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+            if (!EnsureBufferOnWhite()) {
+              return result;
+            }
+            MOZ_ASSERT(mDTBufferOnWhite);
+            mDTBufferOnWhite->CopyRect(IntRect(srcRect.x, srcRect.y, srcRect.width, srcRect.height),
+                                       IntPoint(dest.x, dest.y));
+          }
+          result.mDidSelfCopy = true;
+          mDidSelfCopy = true;
+          // Don't set destBuffer; we special-case self-copies, and
+          // just did the necessary work above.
+          mBufferRect = destBufferRect;
+        } else {
+          // With azure and a data surface perform an buffer unrotate
+          // (SelfCopy).
+          unsigned char* data;
+          IntSize size;
+          int32_t stride;
+          SurfaceFormat format;
+
+          if (mDTBuffer->LockBits(&data, &size, &stride, &format)) {
+            uint8_t bytesPerPixel = BytesPerPixel(format);
+            BufferUnrotate(data,
+                           size.width * bytesPerPixel,
+                           size.height, stride,
+                           newRotation.x * bytesPerPixel, newRotation.y);
+            mDTBuffer->ReleaseBits(data);
+
+            if (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+              if (!EnsureBufferOnWhite()) {
+                return result;
+              }
+              MOZ_ASSERT(mDTBufferOnWhite);
+              mDTBufferOnWhite->LockBits(&data, &size, &stride, &format);
+              uint8_t bytesPerPixel = BytesPerPixel(format);
+              BufferUnrotate(data,
+                             size.width * bytesPerPixel,
+                             size.height, stride,
+                             newRotation.x * bytesPerPixel, newRotation.y);
+              mDTBufferOnWhite->ReleaseBits(data);
+            }
+
+            // Buffer unrotate moves all the pixels, note that
+            // we self copied for SyncBackToFrontBuffer
+            result.mDidSelfCopy = true;
+            mDidSelfCopy = true;
+            mBufferRect = destBufferRect;
+            mBufferRotation = nsIntPoint(0, 0);
+          }
+
+          if (!result.mDidSelfCopy) {
+            destBufferRect = ComputeBufferRect(neededRegion.GetBounds());
+            CreateBuffer(result.mContentType, destBufferRect, bufferFlags,
+                         &destDTBuffer, &destDTBufferOnWhite);
+            if (!destDTBuffer) {
+              return result;
+            }
+          }
+        }
+      } else {
+        mBufferRect = destBufferRect;
+        mBufferRotation = newRotation;
+      }
+    } else {
+      // No pixels are going to be kept. The whole visible region
+      // will be redrawn, so we don't need to copy anything, so we don't
+      // set destBuffer.
+      mBufferRect = destBufferRect;
+      mBufferRotation = nsIntPoint(0,0);
+    }
+  } else {
+    // The buffer's not big enough, so allocate a new one
+    CreateBuffer(result.mContentType, destBufferRect, bufferFlags,
+                 &destDTBuffer, &destDTBufferOnWhite);
+    if (!destDTBuffer) {
+      return result;
+    }
+  }
+
+  NS_ASSERTION(!(aFlags & PAINT_WILL_RESAMPLE) || destBufferRect == neededRegion.GetBounds(),
+               "If we're resampling, we need to validate the entire buffer");
+
+  // If we have no buffered data already, then destBuffer will be a fresh buffer
+  // and we do not need to clear it below.
+  bool isClear = !HaveBuffer();
+
+  if (destDTBuffer) {
+    if (!isClear && (mode != SurfaceMode::SURFACE_COMPONENT_ALPHA || HaveBufferOnWhite())) {
+      // Copy the bits
+      nsIntPoint offset = -destBufferRect.TopLeft();
+      Matrix mat;
+      mat.Translate(offset.x, offset.y);
+      destDTBuffer->SetTransform(mat);
+      if (!EnsureBuffer()) {
+        return result;
+      }
+       MOZ_ASSERT(mDTBuffer, "Have we got a Thebes buffer for some reason?");
+      DrawBufferWithRotation(destDTBuffer, BUFFER_BLACK, 1.0, CompositionOp::OP_SOURCE);
+      destDTBuffer->SetTransform(Matrix());
+
+      if (mode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+        NS_ASSERTION(destDTBufferOnWhite, "Must have a white buffer!");
+        destDTBufferOnWhite->SetTransform(mat);
+        if (!EnsureBufferOnWhite()) {
+          return result;
+        }
+        MOZ_ASSERT(mDTBufferOnWhite, "Have we got a Thebes buffer for some reason?");
+        DrawBufferWithRotation(destDTBufferOnWhite, BUFFER_WHITE, 1.0, CompositionOp::OP_SOURCE);
+        destDTBufferOnWhite->SetTransform(Matrix());
+      }
+    }
+
+    mDTBuffer = destDTBuffer.forget();
+    mDTBufferOnWhite = destDTBufferOnWhite.forget();
+    mBufferRect = destBufferRect;
+    mBufferRotation = nsIntPoint(0,0);
+  }
+  NS_ASSERTION(canHaveRotation || mBufferRotation == nsIntPoint(0,0),
+               "Rotation disabled, but we have nonzero rotation?");
+
+  nsIntRegion invalidate;
+  invalidate.Sub(aLayer->GetValidRegion(), destBufferRect);
+  result.mRegionToInvalidate.Or(result.mRegionToInvalidate, invalidate);
+  result.mClip = DrawRegionClip::DRAW_SNAPPED;
+  result.mMode = mode;
+
+  return result;
+}
+
+DrawTarget*
+RotatedContentBuffer::BorrowDrawTargetForPainting(const PaintState& aPaintState,
+                                                  DrawIterator* aIter /* = nullptr */)
+{
+  if (aPaintState.mMode == SurfaceMode::SURFACE_NONE) {
+    return nullptr;
+  }
+
+  DrawTarget* result = BorrowDrawTargetForQuadrantUpdate(aPaintState.mRegionToDraw.GetBounds(),
+                                                         BUFFER_BOTH, aIter);
+  if (!result) {
+    return nullptr;
+  }
+  const nsIntRegion* drawPtr = &aPaintState.mRegionToDraw;
+  if (aIter) {
+    // The iterators draw region currently only contains the bounds of the region,
+    // this makes it the precise region.
+    aIter->mDrawRegion.And(aIter->mDrawRegion, aPaintState.mRegionToDraw);
+    drawPtr = &aIter->mDrawRegion;
+  }
+
+  if (aPaintState.mMode == SurfaceMode::SURFACE_COMPONENT_ALPHA) {
+    MOZ_ASSERT(mDTBuffer && mDTBufferOnWhite);
+    nsIntRegionRectIterator iter(*drawPtr);
+    const nsIntRect *iterRect;
+    while ((iterRect = iter.Next())) {
+      mDTBuffer->FillRect(Rect(iterRect->x, iterRect->y, iterRect->width, iterRect->height),
+                          ColorPattern(Color(0.0, 0.0, 0.0, 1.0)));
+      mDTBufferOnWhite->FillRect(Rect(iterRect->x, iterRect->y, iterRect->width, iterRect->height),
+                                 ColorPattern(Color(1.0, 1.0, 1.0, 1.0)));
+    }
+  } else if (aPaintState.mContentType == gfxContentType::COLOR_ALPHA && HaveBuffer()) {
+    // HaveBuffer() => we have an existing buffer that we must clear
+    nsIntRegionRectIterator iter(*drawPtr);
+    const nsIntRect *iterRect;
+    while ((iterRect = iter.Next())) {
+      result->ClearRect(Rect(iterRect->x, iterRect->y, iterRect->width, iterRect->height));
+    }
+  }
+
+  return result;
+}
+
+}
+}
+