Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2689 insertions, 0 deletions

diff --git a/gfx/layers/wr/WebRenderCommandBuilder.cpp b/gfx/layers/wr/WebRenderCommandBuilder.cpp
new file mode 100644
index 0000000000..c36349e7b6
--- /dev/null
+++ b/gfx/layers/wr/WebRenderCommandBuilder.cpp
@@ -0,0 +1,2689 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "WebRenderCommandBuilder.h"
+
+#include "BasicLayers.h"
+#include "Layers.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/EffectCompositor.h"
+#include "mozilla/StaticPrefs_gfx.h"
+#include "mozilla/SVGGeometryFrame.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/Logging.h"
+#include "mozilla/gfx/Types.h"
+#include "mozilla/layers/AnimationHelper.h"
+#include "mozilla/layers/ClipManager.h"
+#include "mozilla/layers/ImageClient.h"
+#include "mozilla/layers/RenderRootStateManager.h"
+#include "mozilla/layers/WebRenderBridgeChild.h"
+#include "mozilla/layers/WebRenderLayerManager.h"
+#include "mozilla/layers/IpcResourceUpdateQueue.h"
+#include "mozilla/layers/SharedSurfacesChild.h"
+#include "mozilla/layers/SourceSurfaceSharedData.h"
+#include "mozilla/layers/StackingContextHelper.h"
+#include "mozilla/layers/UpdateImageHelper.h"
+#include "mozilla/layers/WebRenderDrawEventRecorder.h"
+#include "UnitTransforms.h"
+#include "gfxEnv.h"
+#include "nsDisplayListInvalidation.h"
+#include "nsLayoutUtils.h"
+#include "WebRenderCanvasRenderer.h"
+#include "LayerTreeInvalidation.h"
+
+namespace mozilla {
+namespace layers {
+
+using namespace gfx;
+static bool PaintByLayer(nsDisplayItem* aItem,
+                         nsDisplayListBuilder* aDisplayListBuilder,
+                         const RefPtr<BasicLayerManager>& aManager,
+                         gfxContext* aContext, const gfx::Size& aScale,
+                         const std::function<void()>& aPaintFunc);
+static int sIndent;
+#include <stdarg.h>
+#include <stdio.h>
+
+static void GP(const char* fmt, ...) {
+  va_list args;
+  va_start(args, fmt);
+#if 0
+    for (int i = 0; i < sIndent; i++) { printf(" "); }
+    vprintf(fmt, args);
+#endif
+  va_end(args);
+}
+
+// XXX: problems:
+// - How do we deal with scrolling while having only a single invalidation rect?
+// We can have a valid rect and an invalid rect. As we scroll the valid rect
+// will move and the invalid rect will be the new area
+
+struct BlobItemData;
+static void DestroyBlobGroupDataProperty(nsTArray<BlobItemData*>* aArray);
+NS_DECLARE_FRAME_PROPERTY_WITH_DTOR(BlobGroupDataProperty,
+                                    nsTArray<BlobItemData*>,
+                                    DestroyBlobGroupDataProperty);
+
+// These are currently manually allocated and ownership is help by the
+// mDisplayItems hash table in DIGroup
+struct BlobItemData {
+  // a weak pointer to the frame for this item.
+  // DisplayItemData has a mFrameList to deal with merged frames. Hopefully we
+  // don't need to worry about that.
+  nsIFrame* mFrame;
+
+  uint32_t mDisplayItemKey;
+  nsTArray<BlobItemData*>*
+      mArray;  // a weak pointer to the array that's owned by the frame property
+
+  IntRect mRect;
+  // It would be nice to not need this. We need to be able to call
+  // ComputeInvalidationRegion. ComputeInvalidationRegion will sometimes reach
+  // into parent style structs to get information that can change the
+  // invalidation region
+  UniquePtr<nsDisplayItemGeometry> mGeometry;
+  DisplayItemClip mClip;
+  bool mUsed;  // initialized near construction
+  // XXX: only used for debugging
+  bool mInvalid;
+
+  // a weak pointer to the group that owns this item
+  // we use this to track whether group for a particular item has changed
+  struct DIGroup* mGroup;
+
+  // properties that are used to emulate layer tree invalidation
+  Matrix mMatrix;  // updated to track the current transform to device space
+  RefPtr<BasicLayerManager> mLayerManager;
+
+  // We need to keep a list of all the external surfaces used by the blob image.
+  // We do this on a per-display item basis so that the lists remains correct
+  // during invalidations.
+  std::vector<RefPtr<SourceSurface>> mExternalSurfaces;
+
+  IntRect mImageRect;
+
+  BlobItemData(DIGroup* aGroup, nsDisplayItem* aItem)
+      : mUsed(false), mGroup(aGroup) {
+    mInvalid = false;
+    mDisplayItemKey = aItem->GetPerFrameKey();
+    AddFrame(aItem->Frame());
+  }
+
+ private:
+  void AddFrame(nsIFrame* aFrame) {
+    mFrame = aFrame;
+
+    nsTArray<BlobItemData*>* array =
+        aFrame->GetProperty(BlobGroupDataProperty());
+    if (!array) {
+      array = new nsTArray<BlobItemData*>();
+      aFrame->SetProperty(BlobGroupDataProperty(), array);
+    }
+    array->AppendElement(this);
+    mArray = array;
+  }
+
+ public:
+  void ClearFrame() {
+    // Delete the weak pointer to this BlobItemData on the frame
+    MOZ_RELEASE_ASSERT(mFrame);
+    // the property may already be removed if WebRenderUserData got deleted
+    // first so we use our own mArray pointer.
+    mArray->RemoveElement(this);
+
+    // drop the entire property if nothing's left in the array
+    if (mArray->IsEmpty()) {
+      // If the frame is in the process of being destroyed this will fail
+      // but that's ok, because the the property will be removed then anyways
+      mFrame->RemoveProperty(BlobGroupDataProperty());
+    }
+    mFrame = nullptr;
+  }
+
+  ~BlobItemData() {
+    if (mFrame) {
+      ClearFrame();
+    }
+  }
+};
+
+static BlobItemData* GetBlobItemData(nsDisplayItem* aItem) {
+  nsIFrame* frame = aItem->Frame();
+  uint32_t key = aItem->GetPerFrameKey();
+  const nsTArray<BlobItemData*>* array =
+      frame->GetProperty(BlobGroupDataProperty());
+  if (array) {
+    for (BlobItemData* item : *array) {
+      if (item->mDisplayItemKey == key) {
+        return item;
+      }
+    }
+  }
+  return nullptr;
+}
+
+// We keep around the BlobItemData so that when we invalidate it get properly
+// included in the rect
+static void DestroyBlobGroupDataProperty(nsTArray<BlobItemData*>* aArray) {
+  for (BlobItemData* item : *aArray) {
+    GP("DestroyBlobGroupDataProperty: %p-%d\n", item->mFrame,
+       item->mDisplayItemKey);
+    item->mFrame = nullptr;
+  }
+  delete aArray;
+}
+
+static void TakeExternalSurfaces(
+    WebRenderDrawEventRecorder* aRecorder,
+    std::vector<RefPtr<SourceSurface>>& aExternalSurfaces,
+    RenderRootStateManager* aManager, wr::IpcResourceUpdateQueue& aResources) {
+  aRecorder->TakeExternalSurfaces(aExternalSurfaces);
+
+  for (auto& surface : aExternalSurfaces) {
+    // While we don't use the image key with the surface, because the blob image
+    // renderer doesn't have easy access to the resource set, we still want to
+    // ensure one is generated. That will ensure the surface remains alive until
+    // at least the last epoch which the blob image could be used in.
+    wr::ImageKey key;
+    DebugOnly<nsresult> rv =
+        SharedSurfacesChild::Share(surface, aManager, aResources, key);
+    MOZ_ASSERT(rv.value != NS_ERROR_NOT_IMPLEMENTED);
+  }
+}
+
+struct DIGroup;
+struct Grouper {
+  explicit Grouper(ClipManager& aClipManager)
+      : mAppUnitsPerDevPixel(0),
+        mDisplayListBuilder(nullptr),
+        mClipManager(aClipManager) {}
+
+  int32_t mAppUnitsPerDevPixel;
+  nsDisplayListBuilder* mDisplayListBuilder;
+  ClipManager& mClipManager;
+  Matrix mTransform;
+
+  // Paint the list of aChildren display items.
+  void PaintContainerItem(DIGroup* aGroup, nsDisplayItem* aItem,
+                          BlobItemData* aData, const IntRect& aItemBounds,
+                          nsDisplayList* aChildren, gfxContext* aContext,
+                          WebRenderDrawEventRecorder* aRecorder,
+                          RenderRootStateManager* aRootManager,
+                          wr::IpcResourceUpdateQueue& aResources);
+
+  // Builds groups of display items split based on 'layer activity'
+  void ConstructGroups(nsDisplayListBuilder* aDisplayListBuilder,
+                       WebRenderCommandBuilder* aCommandBuilder,
+                       wr::DisplayListBuilder& aBuilder,
+                       wr::IpcResourceUpdateQueue& aResources, DIGroup* aGroup,
+                       nsDisplayList* aList, const StackingContextHelper& aSc);
+  // Builds a group of display items without promoting anything to active.
+  void ConstructGroupInsideInactive(WebRenderCommandBuilder* aCommandBuilder,
+                                    wr::DisplayListBuilder& aBuilder,
+                                    wr::IpcResourceUpdateQueue& aResources,
+                                    DIGroup* aGroup, nsDisplayList* aList,
+                                    const StackingContextHelper& aSc);
+  // Helper method for processing a single inactive item
+  void ConstructItemInsideInactive(WebRenderCommandBuilder* aCommandBuilder,
+                                   wr::DisplayListBuilder& aBuilder,
+                                   wr::IpcResourceUpdateQueue& aResources,
+                                   DIGroup* aGroup, nsDisplayItem* aItem,
+                                   const StackingContextHelper& aSc);
+  ~Grouper() = default;
+};
+
+// Returns whether this is an item for which complete invalidation was
+// reliant on LayerTreeInvalidation in the pre-webrender world.
+static bool IsContainerLayerItem(nsDisplayItem* aItem) {
+  switch (aItem->GetType()) {
+    case DisplayItemType::TYPE_WRAP_LIST:
+    case DisplayItemType::TYPE_CONTAINER:
+    case DisplayItemType::TYPE_TRANSFORM:
+    case DisplayItemType::TYPE_OPACITY:
+    case DisplayItemType::TYPE_FILTER:
+    case DisplayItemType::TYPE_BLEND_CONTAINER:
+    case DisplayItemType::TYPE_BLEND_MODE:
+    case DisplayItemType::TYPE_MASK:
+    case DisplayItemType::TYPE_PERSPECTIVE: {
+      return true;
+    }
+    default: {
+      return false;
+    }
+  }
+}
+
+#include <sstream>
+
+static bool DetectContainerLayerPropertiesBoundsChange(
+    nsDisplayItem* aItem, BlobItemData* aData,
+    nsDisplayItemGeometry& aGeometry) {
+  if (aItem->GetType() == DisplayItemType::TYPE_FILTER) {
+    // Filters go through BasicLayerManager composition which clips to
+    // the BuildingRect
+    aGeometry.mBounds = aGeometry.mBounds.Intersect(aItem->GetBuildingRect());
+  }
+
+  return !aGeometry.mBounds.IsEqualEdges(aData->mGeometry->mBounds);
+}
+
+struct DIGroup {
+  // XXX: Storing owning pointers to the BlobItemData in a hash table is not
+  // a good choice. There are two better options:
+  //
+  // 1. We should just be using a linked list for this stuff.
+  //    That we can iterate over only the used items.
+  //    We remove from the unused list and add to the used list
+  //    when we see an item.
+  //
+  //    we allocate using a free list.
+  //
+  // 2. We can use a Vec and use SwapRemove().
+  //    We'll just need to be careful when iterating.
+  //    The advantage of a Vec is that everything stays compact
+  //    and we don't need to heap allocate the BlobItemData's
+  nsTHashtable<nsPtrHashKey<BlobItemData>> mDisplayItems;
+
+  IntRect mInvalidRect;
+  nsRect mGroupBounds;
+  LayerIntRect mVisibleRect;
+  // This is the last visible rect sent to WebRender. It's used
+  // to compute the invalid rect and ensure that we send
+  // the appropriate data to WebRender for merging.
+  LayerIntRect mLastVisibleRect;
+
+  // This is the intersection of mVisibleRect and mLastVisibleRect
+  // we ensure that mInvalidRect is contained in mPreservedRect
+  IntRect mPreservedRect;
+  IntRect mActualBounds;
+  int32_t mAppUnitsPerDevPixel;
+  gfx::Size mScale;
+  ScrollableLayerGuid::ViewID mScrollId;
+  CompositorHitTestInfo mHitInfo;
+  LayerPoint mResidualOffset;
+  LayerIntRect mLayerBounds;  // mGroupBounds converted to Layer space
+  // mLayerBounds clipped to the container/parent of the
+  // current item being processed.
+  IntRect mClippedImageBounds;  // mLayerBounds with the clipping of any
+                                // containers applied
+  Maybe<wr::BlobImageKey> mKey;
+  std::vector<RefPtr<ScaledFont>> mFonts;
+
+  DIGroup()
+      : mAppUnitsPerDevPixel(0),
+        mScrollId(ScrollableLayerGuid::NULL_SCROLL_ID),
+        mHitInfo(CompositorHitTestInvisibleToHit) {}
+
+  void InvalidateRect(const IntRect& aRect) {
+    auto r = aRect.Intersect(mPreservedRect);
+    // Empty rects get dropped
+    if (!r.IsEmpty()) {
+      mInvalidRect = mInvalidRect.Union(r);
+    }
+  }
+
+  IntRect ItemBounds(nsDisplayItem* aItem) {
+    BlobItemData* data = GetBlobItemData(aItem);
+    return data->mRect;
+  }
+
+  void ClearItems() {
+    GP("items: %d\n", mDisplayItems.Count());
+    for (auto iter = mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
+      BlobItemData* data = iter.Get()->GetKey();
+      GP("Deleting %p-%d\n", data->mFrame, data->mDisplayItemKey);
+      iter.Remove();
+      delete data;
+    }
+  }
+
+  void ClearImageKey(RenderRootStateManager* aManager, bool aForce = false) {
+    if (mKey) {
+      MOZ_RELEASE_ASSERT(aForce || mInvalidRect.IsEmpty());
+      aManager->AddBlobImageKeyForDiscard(*mKey);
+      mKey = Nothing();
+    }
+    mFonts.clear();
+  }
+
+  static IntRect ToDeviceSpace(nsRect aBounds, Matrix& aMatrix,
+                               int32_t aAppUnitsPerDevPixel) {
+    // RoundedOut can convert empty rectangles to non-empty ones
+    // so special case them here
+    if (aBounds.IsEmpty()) {
+      return IntRect();
+    }
+    return RoundedOut(aMatrix.TransformBounds(
+        ToRect(nsLayoutUtils::RectToGfxRect(aBounds, aAppUnitsPerDevPixel))));
+  }
+
+  void ComputeGeometryChange(nsDisplayItem* aItem, BlobItemData* aData,
+                             Matrix& aMatrix, nsDisplayListBuilder* aBuilder) {
+    // If the frame is marked as invalidated, and didn't specify a rect to
+    // invalidate then we want to invalidate both the old and new bounds,
+    // otherwise we only want to invalidate the changed areas. If we do get an
+    // invalid rect, then we want to add this on top of the change areas.
+    nsRect invalid;
+    const DisplayItemClip& clip = aItem->GetClip();
+
+    int32_t appUnitsPerDevPixel =
+        aItem->Frame()->PresContext()->AppUnitsPerDevPixel();
+    MOZ_RELEASE_ASSERT(mAppUnitsPerDevPixel == appUnitsPerDevPixel);
+    GP("\n");
+    GP("clippedImageRect %d %d %d %d\n", mClippedImageBounds.x,
+       mClippedImageBounds.y, mClippedImageBounds.width,
+       mClippedImageBounds.height);
+    LayerIntSize size = mVisibleRect.Size();
+    GP("imageSize: %d %d\n", size.width, size.height);
+    /*if (aItem->IsReused() && aData->mGeometry) {
+      return;
+    }*/
+
+    GP("pre mInvalidRect: %s %p-%d - inv: %d %d %d %d\n", aItem->Name(),
+       aItem->Frame(), aItem->GetPerFrameKey(), mInvalidRect.x, mInvalidRect.y,
+       mInvalidRect.width, mInvalidRect.height);
+    if (!aData->mGeometry) {
+      // This item is being added for the first time, invalidate its entire
+      // area.
+      UniquePtr<nsDisplayItemGeometry> geometry(
+          aItem->AllocateGeometry(aBuilder));
+      nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+          geometry->ComputeInvalidationRegion());
+      aData->mGeometry = std::move(geometry);
+
+      IntRect transformedRect =
+          ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+      aData->mRect = transformedRect.Intersect(mClippedImageBounds);
+      GP("CGC %s %d %d %d %d\n", aItem->Name(), clippedBounds.x,
+         clippedBounds.y, clippedBounds.width, clippedBounds.height);
+      GP("%d %d,  %f %f\n", mVisibleRect.TopLeft().x, mVisibleRect.TopLeft().y,
+         aMatrix._11, aMatrix._22);
+      GP("mRect %d %d %d %d\n", aData->mRect.x, aData->mRect.y,
+         aData->mRect.width, aData->mRect.height);
+      InvalidateRect(aData->mRect);
+      aData->mInvalid = true;
+    } else if (aData->mInvalid ||
+               /* XXX: handle image load invalidation */ (
+                   aItem->IsInvalid(invalid) && invalid.IsEmpty())) {
+      UniquePtr<nsDisplayItemGeometry> geometry(
+          aItem->AllocateGeometry(aBuilder));
+      nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+          geometry->ComputeInvalidationRegion());
+      aData->mGeometry = std::move(geometry);
+
+      GP("matrix: %f %f\n", aMatrix._31, aMatrix._32);
+      GP("frame invalid invalidate: %s\n", aItem->Name());
+      GP("old rect: %d %d %d %d\n", aData->mRect.x, aData->mRect.y,
+         aData->mRect.width, aData->mRect.height);
+      InvalidateRect(aData->mRect);
+      // We want to snap to outside pixels. When should we multiply by the
+      // matrix?
+      // XXX: TransformBounds is expensive. We should avoid doing it if we have
+      // no transform
+      IntRect transformedRect =
+          ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+      aData->mRect = transformedRect.Intersect(mClippedImageBounds);
+      InvalidateRect(aData->mRect);
+      GP("new rect: %d %d %d %d\n", aData->mRect.x, aData->mRect.y,
+         aData->mRect.width, aData->mRect.height);
+      aData->mInvalid = true;
+    } else {
+      GP("else invalidate: %s\n", aItem->Name());
+      nsRegion combined;
+      // this includes situations like reflow changing the position
+      aItem->ComputeInvalidationRegion(aBuilder, aData->mGeometry.get(),
+                                       &combined);
+      if (!combined.IsEmpty()) {
+        // There might be no point in doing this elaborate tracking here to get
+        // smaller areas
+        InvalidateRect(aData->mRect);  // invalidate the old area -- in theory
+                                       // combined should take care of this
+        UniquePtr<nsDisplayItemGeometry> geometry(
+            aItem->AllocateGeometry(aBuilder));
+        // invalidate the invalidated area.
+
+        aData->mGeometry = std::move(geometry);
+
+        nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+            aData->mGeometry->ComputeInvalidationRegion());
+        IntRect transformedRect =
+            ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+        aData->mRect = transformedRect.Intersect(mClippedImageBounds);
+        InvalidateRect(aData->mRect);
+
+        aData->mInvalid = true;
+      } else {
+        if (aData->mClip != clip) {
+          UniquePtr<nsDisplayItemGeometry> geometry(
+              aItem->AllocateGeometry(aBuilder));
+          if (!IsContainerLayerItem(aItem)) {
+            // the bounds of layer items can change on us without
+            // ComputeInvalidationRegion returning any change. Other items
+            // shouldn't have any hidden geometry change.
+            MOZ_RELEASE_ASSERT(
+                geometry->mBounds.IsEqualEdges(aData->mGeometry->mBounds));
+          } else {
+            aData->mGeometry = std::move(geometry);
+          }
+          nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+              aData->mGeometry->ComputeInvalidationRegion());
+          IntRect transformedRect =
+              ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+          InvalidateRect(aData->mRect);
+          aData->mRect = transformedRect.Intersect(mClippedImageBounds);
+          InvalidateRect(aData->mRect);
+
+          GP("ClipChange: %s %d %d %d %d\n", aItem->Name(), aData->mRect.x,
+             aData->mRect.y, aData->mRect.XMost(), aData->mRect.YMost());
+
+        } else if (!aMatrix.ExactlyEquals(aData->mMatrix)) {
+          // We haven't detected any changes so far. Unfortunately we don't
+          // currently have a good way of checking if the transform has changed
+          // so we just store it and see if it see if it has changed.
+          // If we want this to go faster, we can probably put a flag on the
+          // frame using the style sytem UpdateTransformLayer hint and check for
+          // that.
+
+          UniquePtr<nsDisplayItemGeometry> geometry(
+              aItem->AllocateGeometry(aBuilder));
+          if (!IsContainerLayerItem(aItem)) {
+            // the bounds of layer items can change on us
+            // other items shouldn't
+            MOZ_RELEASE_ASSERT(
+                geometry->mBounds.IsEqualEdges(aData->mGeometry->mBounds));
+          } else {
+            aData->mGeometry = std::move(geometry);
+          }
+          nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+              aData->mGeometry->ComputeInvalidationRegion());
+          IntRect transformedRect =
+              ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+          InvalidateRect(aData->mRect);
+          aData->mRect = transformedRect.Intersect(mClippedImageBounds);
+          InvalidateRect(aData->mRect);
+
+          GP("TransformChange: %s %d %d %d %d\n", aItem->Name(), aData->mRect.x,
+             aData->mRect.y, aData->mRect.XMost(), aData->mRect.YMost());
+        } else if (IsContainerLayerItem(aItem)) {
+          UniquePtr<nsDisplayItemGeometry> geometry(
+              aItem->AllocateGeometry(aBuilder));
+          // we need to catch bounds changes of containers so that we continue
+          // to have the correct bounds rects in the recording
+          if (DetectContainerLayerPropertiesBoundsChange(aItem, aData,
+                                                         *geometry)) {
+            nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+                geometry->ComputeInvalidationRegion());
+            aData->mGeometry = std::move(geometry);
+            IntRect transformedRect =
+                ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+            InvalidateRect(aData->mRect);
+            aData->mRect = transformedRect.Intersect(mClippedImageBounds);
+            InvalidateRect(aData->mRect);
+            GP("DetectContainerLayerPropertiesBoundsChange change\n");
+          } else {
+            // Handle changes in mClippedImageBounds
+            nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+                geometry->ComputeInvalidationRegion());
+            IntRect transformedRect =
+                ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+            auto rect = transformedRect.Intersect(mClippedImageBounds);
+            if (!rect.IsEqualEdges(aData->mRect)) {
+              GP("ContainerLayer image rect bounds change\n");
+              InvalidateRect(aData->mRect);
+              aData->mRect = rect;
+              InvalidateRect(aData->mRect);
+            } else {
+              GP("Layer NoChange: %s %d %d %d %d\n", aItem->Name(),
+                 aData->mRect.x, aData->mRect.y, aData->mRect.XMost(),
+                 aData->mRect.YMost());
+            }
+          }
+        } else {
+          UniquePtr<nsDisplayItemGeometry> geometry(
+              aItem->AllocateGeometry(aBuilder));
+          nsRect clippedBounds = clip.ApplyNonRoundedIntersection(
+              geometry->ComputeInvalidationRegion());
+          IntRect transformedRect =
+              ToDeviceSpace(clippedBounds, aMatrix, appUnitsPerDevPixel);
+          auto rect = transformedRect.Intersect(mClippedImageBounds);
+          // Make sure we update mRect for mClippedImageBounds changes
+          if (!rect.IsEqualEdges(aData->mRect)) {
+            GP("ContainerLayer image rect bounds change\n");
+            InvalidateRect(aData->mRect);
+            aData->mRect = rect;
+            InvalidateRect(aData->mRect);
+          } else {
+            GP("NoChange: %s %d %d %d %d\n", aItem->Name(), aData->mRect.x,
+               aData->mRect.y, aData->mRect.XMost(), aData->mRect.YMost());
+          }
+        }
+      }
+    }
+    mActualBounds.OrWith(aData->mRect);
+    aData->mClip = clip;
+    aData->mMatrix = aMatrix;
+    aData->mImageRect = mClippedImageBounds;
+    GP("post mInvalidRect: %d %d %d %d\n", mInvalidRect.x, mInvalidRect.y,
+       mInvalidRect.width, mInvalidRect.height);
+  }
+
+  void EndGroup(WebRenderLayerManager* aWrManager,
+                nsDisplayListBuilder* aDisplayListBuilder,
+                wr::DisplayListBuilder& aBuilder,
+                wr::IpcResourceUpdateQueue& aResources, Grouper* aGrouper,
+                nsDisplayItem* aStartItem, nsDisplayItem* aEndItem) {
+    GP("\n\n");
+    GP("Begin EndGroup\n");
+
+    mVisibleRect = mVisibleRect.Intersect(ViewAs<LayerPixel>(
+        mActualBounds, PixelCastJustification::LayerIsImage));
+
+    if (mVisibleRect.IsEmpty()) {
+      return;
+    }
+
+    // Invalidate any unused items
+    GP("mDisplayItems\n");
+    for (auto iter = mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
+      BlobItemData* data = iter.Get()->GetKey();
+      GP("  : %p-%d\n", data->mFrame, data->mDisplayItemKey);
+      if (!data->mUsed) {
+        GP("Invalidate unused: %p-%d\n", data->mFrame, data->mDisplayItemKey);
+        InvalidateRect(data->mRect);
+        iter.Remove();
+        delete data;
+      } else {
+        data->mUsed = false;
+      }
+    }
+
+    IntSize dtSize = mVisibleRect.Size().ToUnknownSize();
+    // The actual display item's size shouldn't have the scale factored in
+    // Round the bounds out to leave space for unsnapped content
+    LayoutDeviceToLayerScale2D scale(mScale.width, mScale.height);
+    LayoutDeviceRect itemBounds =
+        (LayerRect(mVisibleRect) - mResidualOffset) / scale;
+
+    if (mInvalidRect.IsEmpty() && mVisibleRect.IsEqualEdges(mLastVisibleRect)) {
+      GP("Not repainting group because it's empty\n");
+      GP("End EndGroup\n");
+      if (mKey) {
+        // Although the contents haven't changed, the visible area *may* have,
+        // so request it be updated unconditionally (wr should be able to easily
+        // detect if this is a no-op on its side, if that matters)
+        aResources.SetBlobImageVisibleArea(
+            *mKey, ViewAs<ImagePixel>(mVisibleRect,
+                                      PixelCastJustification::LayerIsImage));
+        mLastVisibleRect = mVisibleRect;
+        PushImage(aBuilder, itemBounds);
+      }
+      return;
+    }
+
+    gfx::SurfaceFormat format = gfx::SurfaceFormat::B8G8R8A8;
+    std::vector<RefPtr<ScaledFont>> fonts;
+    bool validFonts = true;
+    RefPtr<WebRenderDrawEventRecorder> recorder =
+        MakeAndAddRef<WebRenderDrawEventRecorder>(
+            [&](MemStream& aStream,
+                std::vector<RefPtr<ScaledFont>>& aScaledFonts) {
+              size_t count = aScaledFonts.size();
+              aStream.write((const char*)&count, sizeof(count));
+              for (auto& scaled : aScaledFonts) {
+                Maybe<wr::FontInstanceKey> key =
+                    aWrManager->WrBridge()->GetFontKeyForScaledFont(
+                        scaled, &aResources);
+                if (key.isNothing()) {
+                  validFonts = false;
+                  break;
+                }
+                BlobFont font = {key.value(), scaled};
+                aStream.write((const char*)&font, sizeof(font));
+              }
+              fonts = std::move(aScaledFonts);
+            });
+
+    RefPtr<gfx::DrawTarget> dummyDt = gfx::Factory::CreateDrawTarget(
+        gfx::BackendType::SKIA, gfx::IntSize(1, 1), format);
+
+    RefPtr<gfx::DrawTarget> dt = gfx::Factory::CreateRecordingDrawTarget(
+        recorder, dummyDt, mLayerBounds.ToUnknownRect());
+    // Setup the gfxContext
+    RefPtr<gfxContext> context = gfxContext::CreateOrNull(dt);
+    context->SetMatrix(
+        Matrix::Scaling(mScale.width, mScale.height)
+            .PostTranslate(mResidualOffset.x, mResidualOffset.y));
+
+    GP("mInvalidRect: %d %d %d %d\n", mInvalidRect.x, mInvalidRect.y,
+       mInvalidRect.width, mInvalidRect.height);
+
+    RenderRootStateManager* rootManager =
+        aWrManager->GetRenderRootStateManager();
+    bool empty = aStartItem == aEndItem;
+    if (empty) {
+      ClearImageKey(rootManager, true);
+      return;
+    }
+
+    // Reset mHitInfo, it will get updated inside PaintItemRange
+    mHitInfo = CompositorHitTestInvisibleToHit;
+
+    PaintItemRange(aGrouper, aStartItem, aEndItem, context, recorder,
+                   rootManager, aResources);
+
+    // XXX: set this correctly perhaps using
+    // aItem->GetOpaqueRegion(aDisplayListBuilder, &snapped).
+    //   Contains(paintBounds);?
+    wr::OpacityType opacity = wr::OpacityType::HasAlphaChannel;
+
+    bool hasItems = recorder->Finish();
+    GP("%d Finish\n", hasItems);
+    if (!validFonts) {
+      gfxCriticalNote << "Failed serializing fonts for blob image";
+      return;
+    }
+    Range<uint8_t> bytes((uint8_t*)recorder->mOutputStream.mData,
+                         recorder->mOutputStream.mLength);
+    if (!mKey) {
+      // we don't want to send a new image that doesn't have any
+      // items in it
+      if (!hasItems || mVisibleRect.IsEmpty()) {
+        return;
+      }
+
+      wr::BlobImageKey key =
+          wr::BlobImageKey{aWrManager->WrBridge()->GetNextImageKey()};
+      GP("No previous key making new one %d\n", key._0.mHandle);
+      wr::ImageDescriptor descriptor(dtSize, 0, dt->GetFormat(), opacity);
+      MOZ_RELEASE_ASSERT(bytes.length() > sizeof(size_t));
+      if (!aResources.AddBlobImage(
+              key, descriptor, bytes,
+              ViewAs<ImagePixel>(mVisibleRect,
+                                 PixelCastJustification::LayerIsImage))) {
+        return;
+      }
+      mKey = Some(key);
+    } else {
+      wr::ImageDescriptor descriptor(dtSize, 0, dt->GetFormat(), opacity);
+
+      // Convert mInvalidRect to image space by subtracting the corner of the
+      // image bounds
+      auto dirtyRect = ViewAs<ImagePixel>(mInvalidRect);
+
+      auto bottomRight = dirtyRect.BottomRight();
+      GP("check invalid %d %d - %d %d\n", bottomRight.x, bottomRight.y,
+         dtSize.width, dtSize.height);
+      GP("Update Blob %d %d %d %d\n", mInvalidRect.x, mInvalidRect.y,
+         mInvalidRect.width, mInvalidRect.height);
+      if (!aResources.UpdateBlobImage(
+              *mKey, descriptor, bytes,
+              ViewAs<ImagePixel>(mVisibleRect,
+                                 PixelCastJustification::LayerIsImage),
+              dirtyRect)) {
+        return;
+      }
+    }
+    mFonts = std::move(fonts);
+    aResources.SetBlobImageVisibleArea(
+        *mKey,
+        ViewAs<ImagePixel>(mVisibleRect, PixelCastJustification::LayerIsImage));
+    mLastVisibleRect = mVisibleRect;
+    PushImage(aBuilder, itemBounds);
+    GP("End EndGroup\n\n");
+  }
+
+  void PushImage(wr::DisplayListBuilder& aBuilder,
+                 const LayoutDeviceRect& bounds) {
+    wr::LayoutRect dest = wr::ToLayoutRect(bounds);
+    GP("PushImage: %f %f %f %f\n", dest.origin.x, dest.origin.y,
+       dest.size.width, dest.size.height);
+    gfx::SamplingFilter sampleFilter = gfx::SamplingFilter::
+        LINEAR;  // nsLayoutUtils::GetSamplingFilterForFrame(aItem->Frame());
+    bool backfaceHidden = false;
+
+    // We don't really know the exact shape of this blob because it may contain
+    // SVG shapes. Also mHitInfo may be a combination of hit info flags from
+    // different shapes so generate an irregular-area hit-test region for it.
+    CompositorHitTestInfo hitInfo = mHitInfo;
+    if (hitInfo.contains(CompositorHitTestFlags::eVisibleToHitTest)) {
+      hitInfo += CompositorHitTestFlags::eIrregularArea;
+    }
+
+    // XXX - clipping the item against the paint rect breaks some content.
+    // cf. Bug 1455422.
+    // wr::LayoutRect clip = wr::ToLayoutRect(bounds.Intersect(mVisibleRect));
+
+    aBuilder.PushHitTest(dest, dest, !backfaceHidden, mScrollId, hitInfo,
+                         SideBits::eNone);
+
+    aBuilder.PushImage(dest, dest, !backfaceHidden,
+                       wr::ToImageRendering(sampleFilter),
+                       wr::AsImageKey(*mKey));
+  }
+
+  void PaintItemRange(Grouper* aGrouper, nsDisplayItem* aStartItem,
+                      nsDisplayItem* aEndItem, gfxContext* aContext,
+                      WebRenderDrawEventRecorder* aRecorder,
+                      RenderRootStateManager* aRootManager,
+                      wr::IpcResourceUpdateQueue& aResources) {
+    LayerIntSize size = mVisibleRect.Size();
+    for (nsDisplayItem* item = aStartItem; item != aEndItem;
+         item = item->GetAbove()) {
+      BlobItemData* data = GetBlobItemData(item);
+      IntRect bounds = data->mRect;
+      auto bottomRight = bounds.BottomRight();
+
+      GP("Trying %s %p-%d %d %d %d %d\n", item->Name(), item->Frame(),
+         item->GetPerFrameKey(), bounds.x, bounds.y, bounds.XMost(),
+         bounds.YMost());
+
+      if (item->GetType() == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
+        // Accumulate the hit-test info flags. In cases where there are multiple
+        // hittest-info display items with different flags, mHitInfo will have
+        // the union of all those flags. If that is the case, we will
+        // additionally set eIrregularArea (at the site that we use mHitInfo)
+        // so that downstream consumers of this (primarily APZ) will know that
+        // the exact shape of what gets hit with what is unknown.
+        mHitInfo +=
+            static_cast<nsDisplayCompositorHitTestInfo*>(item)->HitTestFlags();
+        continue;
+      }
+
+      GP("paint check invalid %d %d - %d %d\n", bottomRight.x, bottomRight.y,
+         size.width, size.height);
+      // skip empty items
+      if (bounds.IsEmpty()) {
+        continue;
+      }
+
+      bool dirty = true;
+      auto preservedBounds = bounds.Intersect(mPreservedRect);
+      if (!mInvalidRect.Contains(preservedBounds)) {
+        GP("Passing\n");
+        dirty = false;
+        BlobItemData* data = GetBlobItemData(item);
+        if (data->mInvalid) {
+          gfxCriticalError()
+              << "DisplayItem" << item->Name() << "-should be invalid";
+        }
+        // if the item is invalid it needs to be fully contained
+        MOZ_RELEASE_ASSERT(!data->mInvalid);
+      }
+
+      nsDisplayList* children = item->GetChildren();
+      if (children) {
+        GP("doing children in EndGroup\n");
+        aGrouper->PaintContainerItem(this, item, data, bounds, children,
+                                     aContext, aRecorder, aRootManager,
+                                     aResources);
+        continue;
+      }
+      nsPaintedDisplayItem* paintedItem = item->AsPaintedDisplayItem();
+      if (!paintedItem) {
+        continue;
+      }
+      if (dirty) {
+        // What should the clip settting strategy be? We can set the full
+        // clip everytime. this is probably easiest for now. An alternative
+        // would be to put the push and the pop into separate items and let
+        // invalidation handle it that way.
+        DisplayItemClip currentClip = paintedItem->GetClip();
+
+        if (currentClip.HasClip()) {
+          aContext->Save();
+          currentClip.ApplyTo(aContext, aGrouper->mAppUnitsPerDevPixel);
+        }
+        aContext->NewPath();
+        GP("painting %s %p-%d\n", paintedItem->Name(), paintedItem->Frame(),
+           paintedItem->GetPerFrameKey());
+        if (aGrouper->mDisplayListBuilder->IsPaintingToWindow()) {
+          paintedItem->Frame()->AddStateBits(NS_FRAME_PAINTED_THEBES);
+        }
+
+        paintedItem->Paint(aGrouper->mDisplayListBuilder, aContext);
+        TakeExternalSurfaces(aRecorder, data->mExternalSurfaces, aRootManager,
+                             aResources);
+
+        if (currentClip.HasClip()) {
+          aContext->Restore();
+        }
+      }
+      aContext->GetDrawTarget()->FlushItem(bounds);
+    }
+  }
+
+  ~DIGroup() {
+    GP("Group destruct\n");
+    for (auto iter = mDisplayItems.Iter(); !iter.Done(); iter.Next()) {
+      BlobItemData* data = iter.Get()->GetKey();
+      GP("Deleting %p-%d\n", data->mFrame, data->mDisplayItemKey);
+      iter.Remove();
+      delete data;
+    }
+  }
+};
+
+// If we have an item we need to make sure it matches the current group
+// otherwise it means the item switched groups and we need to invalidate
+// it and recreate the data.
+static BlobItemData* GetBlobItemDataForGroup(nsDisplayItem* aItem,
+                                             DIGroup* aGroup) {
+  BlobItemData* data = GetBlobItemData(aItem);
+  if (data) {
+    MOZ_RELEASE_ASSERT(data->mGroup->mDisplayItems.Contains(data));
+    if (data->mGroup != aGroup) {
+      GP("group don't match %p %p\n", data->mGroup, aGroup);
+      data->ClearFrame();
+      // the item is for another group
+      // it should be cleared out as being unused at the end of this paint
+      data = nullptr;
+    }
+  }
+  if (!data) {
+    GP("Allocating blob data\n");
+    data = new BlobItemData(aGroup, aItem);
+    aGroup->mDisplayItems.PutEntry(data);
+  }
+  data->mUsed = true;
+  return data;
+}
+
+void Grouper::PaintContainerItem(DIGroup* aGroup, nsDisplayItem* aItem,
+                                 BlobItemData* aData,
+                                 const IntRect& aItemBounds,
+                                 nsDisplayList* aChildren, gfxContext* aContext,
+                                 WebRenderDrawEventRecorder* aRecorder,
+                                 RenderRootStateManager* aRootManager,
+                                 wr::IpcResourceUpdateQueue& aResources) {
+  switch (aItem->GetType()) {
+    case DisplayItemType::TYPE_TRANSFORM: {
+      DisplayItemClip currentClip = aItem->GetClip();
+
+      gfxContextMatrixAutoSaveRestore saveMatrix;
+      if (currentClip.HasClip()) {
+        aContext->Save();
+        currentClip.ApplyTo(aContext, this->mAppUnitsPerDevPixel);
+        aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      } else {
+        saveMatrix.SetContext(aContext);
+      }
+
+      auto transformItem = static_cast<nsDisplayTransform*>(aItem);
+      Matrix4x4Flagged trans = transformItem->GetTransform();
+      Matrix trans2d;
+      if (!trans.Is2D(&trans2d)) {
+        // We don't currently support doing invalidation inside 3d transforms.
+        // For now just paint it as a single item.
+        BlobItemData* data = GetBlobItemDataForGroup(aItem, aGroup);
+        if (data->mLayerManager->GetRoot()) {
+          data->mLayerManager->BeginTransaction();
+          data->mLayerManager->EndTransaction(
+              FrameLayerBuilder::DrawPaintedLayer, mDisplayListBuilder);
+          TakeExternalSurfaces(aRecorder, data->mExternalSurfaces, aRootManager,
+                               aResources);
+          aContext->GetDrawTarget()->FlushItem(aItemBounds);
+        }
+      } else {
+        aContext->Multiply(ThebesMatrix(trans2d));
+        aGroup->PaintItemRange(this, aChildren->GetBottom(), nullptr, aContext,
+                               aRecorder, aRootManager, aResources);
+      }
+
+      if (currentClip.HasClip()) {
+        aContext->Restore();
+        aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      }
+      break;
+    }
+    case DisplayItemType::TYPE_OPACITY: {
+      auto opacityItem = static_cast<nsDisplayOpacity*>(aItem);
+      float opacity = opacityItem->GetOpacity();
+      if (opacity == 0.0f) {
+        return;
+      }
+
+      aContext->GetDrawTarget()->PushLayer(false, opacityItem->GetOpacity(),
+                                           nullptr, mozilla::gfx::Matrix(),
+                                           aItemBounds);
+      GP("beginGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+         aItem->GetPerFrameKey());
+      aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      aGroup->PaintItemRange(this, aChildren->GetBottom(), nullptr, aContext,
+                             aRecorder, aRootManager, aResources);
+      aContext->GetDrawTarget()->PopLayer();
+      GP("endGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+         aItem->GetPerFrameKey());
+      aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      break;
+    }
+    case DisplayItemType::TYPE_BLEND_MODE: {
+      auto blendItem = static_cast<nsDisplayBlendMode*>(aItem);
+      auto blendMode = blendItem->BlendMode();
+      aContext->GetDrawTarget()->PushLayerWithBlend(
+          false, 1.0, nullptr, mozilla::gfx::Matrix(), aItemBounds, false,
+          blendMode);
+      GP("beginGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+         aItem->GetPerFrameKey());
+      aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      aGroup->PaintItemRange(this, aChildren->GetBottom(), nullptr, aContext,
+                             aRecorder, aRootManager, aResources);
+      aContext->GetDrawTarget()->PopLayer();
+      GP("endGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+         aItem->GetPerFrameKey());
+      aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      break;
+    }
+    case DisplayItemType::TYPE_BLEND_CONTAINER: {
+      aContext->GetDrawTarget()->PushLayer(false, 1.0, nullptr,
+                                           mozilla::gfx::Matrix(), aItemBounds);
+      GP("beginGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+         aItem->GetPerFrameKey());
+      aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      aGroup->PaintItemRange(this, aChildren->GetBottom(), nullptr, aContext,
+                             aRecorder, aRootManager, aResources);
+      aContext->GetDrawTarget()->PopLayer();
+      GP("endGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+         aItem->GetPerFrameKey());
+      aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      break;
+    }
+    case DisplayItemType::TYPE_MASK: {
+      GP("Paint Mask\n");
+      auto maskItem = static_cast<nsDisplayMasksAndClipPaths*>(aItem);
+      maskItem->SetPaintRect(maskItem->GetClippedBounds(mDisplayListBuilder));
+      if (maskItem->IsValidMask()) {
+        maskItem->PaintWithContentsPaintCallback(
+            mDisplayListBuilder, aContext, [&] {
+              GP("beginGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+                 aItem->GetPerFrameKey());
+              aContext->GetDrawTarget()->FlushItem(aItemBounds);
+              aGroup->PaintItemRange(this, aChildren->GetBottom(), nullptr,
+                                     aContext, aRecorder, aRootManager,
+                                     aResources);
+              GP("endGroup %s %p-%d\n", aItem->Name(), aItem->Frame(),
+                 aItem->GetPerFrameKey());
+            });
+        TakeExternalSurfaces(aRecorder, aData->mExternalSurfaces, aRootManager,
+                             aResources);
+        aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      }
+      break;
+    }
+    case DisplayItemType::TYPE_FILTER: {
+      GP("Paint Filter\n");
+      // We don't currently support doing invalidation inside nsDisplayFilters
+      // for now just paint it as a single item
+      BlobItemData* data = GetBlobItemDataForGroup(aItem, aGroup);
+      if (data->mLayerManager->GetRoot()) {
+        data->mLayerManager->BeginTransaction();
+        static_cast<nsDisplayFilters*>(aItem)->PaintAsLayer(
+            mDisplayListBuilder, aContext, data->mLayerManager);
+        if (data->mLayerManager->InTransaction()) {
+          data->mLayerManager->AbortTransaction();
+        }
+        TakeExternalSurfaces(aRecorder, data->mExternalSurfaces, aRootManager,
+                             aResources);
+        aContext->GetDrawTarget()->FlushItem(aItemBounds);
+      }
+      break;
+    }
+
+    default:
+      aGroup->PaintItemRange(this, aChildren->GetBottom(), nullptr, aContext,
+                             aRecorder, aRootManager, aResources);
+      break;
+  }
+}
+
+class WebRenderGroupData : public WebRenderUserData {
+ public:
+  WebRenderGroupData(RenderRootStateManager* aWRManager, nsDisplayItem* aItem);
+  virtual ~WebRenderGroupData();
+
+  WebRenderGroupData* AsGroupData() override { return this; }
+  UserDataType GetType() override { return UserDataType::eGroup; }
+  static UserDataType Type() { return UserDataType::eGroup; }
+
+  DIGroup mSubGroup;
+  DIGroup mFollowingGroup;
+};
+
+static bool IsItemProbablyActive(
+    nsDisplayItem* aItem, mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder, bool aSiblingActive);
+
+static bool HasActiveChildren(const nsDisplayList& aList,
+                              mozilla::wr::DisplayListBuilder& aBuilder,
+                              mozilla::wr::IpcResourceUpdateQueue& aResources,
+                              const mozilla::layers::StackingContextHelper& aSc,
+                              mozilla::layers::RenderRootStateManager* aManager,
+                              nsDisplayListBuilder* aDisplayListBuilder) {
+  for (nsDisplayItem* i = aList.GetBottom(); i; i = i->GetAbove()) {
+    if (IsItemProbablyActive(i, aBuilder, aResources, aSc, aManager,
+                             aDisplayListBuilder, false)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// This function decides whether we want to treat this item as "active", which
+// means that it's a container item which we will turn into a WebRender
+// StackingContext, or whether we treat it as "inactive" and include it inside
+// the parent blob image.
+//
+// We can't easily use GetLayerState because it wants a bunch of layers related
+// information.
+static bool IsItemProbablyActive(
+    nsDisplayItem* aItem, mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const mozilla::layers::StackingContextHelper& aSc,
+    mozilla::layers::RenderRootStateManager* aManager,
+    nsDisplayListBuilder* aDisplayListBuilder,
+    bool aHasActivePrecedingSibling) {
+  switch (aItem->GetType()) {
+    case DisplayItemType::TYPE_TRANSFORM: {
+      nsDisplayTransform* transformItem =
+          static_cast<nsDisplayTransform*>(aItem);
+      const Matrix4x4Flagged& t = transformItem->GetTransform();
+      Matrix t2d;
+      bool is2D = t.Is2D(&t2d);
+      GP("active: %d\n", transformItem->MayBeAnimated(aDisplayListBuilder));
+      return transformItem->MayBeAnimated(aDisplayListBuilder, false) ||
+             !is2D ||
+             HasActiveChildren(*transformItem->GetChildren(), aBuilder,
+                               aResources, aSc, aManager, aDisplayListBuilder);
+    }
+    case DisplayItemType::TYPE_OPACITY: {
+      nsDisplayOpacity* opacityItem = static_cast<nsDisplayOpacity*>(aItem);
+      bool active = opacityItem->NeedsActiveLayer(aDisplayListBuilder,
+                                                  opacityItem->Frame(), false);
+      GP("active: %d\n", active);
+      return active ||
+             HasActiveChildren(*opacityItem->GetChildren(), aBuilder,
+                               aResources, aSc, aManager, aDisplayListBuilder);
+    }
+    case DisplayItemType::TYPE_FOREIGN_OBJECT: {
+      return true;
+    }
+    case DisplayItemType::TYPE_SVG_GEOMETRY: {
+      if (StaticPrefs::gfx_webrender_svg_images()) {
+        auto* svgItem = static_cast<DisplaySVGGeometry*>(aItem);
+        return svgItem->ShouldBeActive(aBuilder, aResources, aSc, aManager,
+                                       aDisplayListBuilder);
+      }
+      return false;
+    }
+    case DisplayItemType::TYPE_BLEND_MODE: {
+      /* BLEND_MODE needs to be active if it might have a previous sibling
+       * that is active so that it's able to blend with that content. */
+      return aHasActivePrecedingSibling ||
+             HasActiveChildren(*aItem->GetChildren(), aBuilder, aResources, aSc,
+                               aManager, aDisplayListBuilder);
+    }
+    case DisplayItemType::TYPE_WRAP_LIST:
+    case DisplayItemType::TYPE_CONTAINER:
+    case DisplayItemType::TYPE_MASK:
+    case DisplayItemType::TYPE_PERSPECTIVE: {
+      if (aItem->GetChildren()) {
+        return HasActiveChildren(*aItem->GetChildren(), aBuilder, aResources,
+                                 aSc, aManager, aDisplayListBuilder);
+      }
+      return false;
+    }
+    case DisplayItemType::TYPE_FILTER: {
+      nsDisplayFilters* filters = static_cast<nsDisplayFilters*>(aItem);
+      return filters->CanCreateWebRenderCommands();
+    }
+    default:
+      // TODO: handle other items?
+      return false;
+  }
+}
+
+// This does a pass over the display lists and will join the display items
+// into groups as well as paint them
+void Grouper::ConstructGroups(nsDisplayListBuilder* aDisplayListBuilder,
+                              WebRenderCommandBuilder* aCommandBuilder,
+                              wr::DisplayListBuilder& aBuilder,
+                              wr::IpcResourceUpdateQueue& aResources,
+                              DIGroup* aGroup, nsDisplayList* aList,
+                              const StackingContextHelper& aSc) {
+  DIGroup* currentGroup = aGroup;
+
+  nsDisplayItem* item = aList->GetBottom();
+  nsDisplayItem* startOfCurrentGroup = item;
+  RenderRootStateManager* manager =
+      aCommandBuilder->mManager->GetRenderRootStateManager();
+  // We need to track whether we have active siblings for mixed blend mode.
+  bool encounteredActiveItem = false;
+  while (item) {
+    if (IsItemProbablyActive(item, aBuilder, aResources, aSc, manager,
+                             mDisplayListBuilder, encounteredActiveItem)) {
+      encounteredActiveItem = true;
+      // We're going to be starting a new group.
+      RefPtr<WebRenderGroupData> groupData =
+          aCommandBuilder->CreateOrRecycleWebRenderUserData<WebRenderGroupData>(
+              item);
+
+      groupData->mFollowingGroup.mInvalidRect.SetEmpty();
+
+      // Initialize groupData->mFollowingGroup with data from currentGroup.
+      // We want to copy out this information before calling EndGroup because
+      // EndGroup will set mLastVisibleRect depending on whether
+      // we send something to WebRender.
+
+      // TODO: compute the group bounds post-grouping, so that they can be
+      // tighter for just the sublist that made it into this group.
+      // We want to ensure the tight bounds are still clipped by area
+      // that we're building the display list for.
+      if (groupData->mFollowingGroup.mScale != currentGroup->mScale ||
+          groupData->mFollowingGroup.mAppUnitsPerDevPixel !=
+              currentGroup->mAppUnitsPerDevPixel ||
+          groupData->mFollowingGroup.mResidualOffset !=
+              currentGroup->mResidualOffset) {
+        if (groupData->mFollowingGroup.mAppUnitsPerDevPixel !=
+            currentGroup->mAppUnitsPerDevPixel) {
+          GP("app unit change following: %d %d\n",
+             groupData->mFollowingGroup.mAppUnitsPerDevPixel,
+             currentGroup->mAppUnitsPerDevPixel);
+        }
+        // The group changed size
+        GP("Inner group size change\n");
+        groupData->mFollowingGroup.ClearItems();
+        groupData->mFollowingGroup.ClearImageKey(
+            aCommandBuilder->mManager->GetRenderRootStateManager());
+      }
+      groupData->mFollowingGroup.mGroupBounds = currentGroup->mGroupBounds;
+      groupData->mFollowingGroup.mAppUnitsPerDevPixel =
+          currentGroup->mAppUnitsPerDevPixel;
+      groupData->mFollowingGroup.mLayerBounds = currentGroup->mLayerBounds;
+      groupData->mFollowingGroup.mClippedImageBounds =
+          currentGroup->mClippedImageBounds;
+      groupData->mFollowingGroup.mScale = currentGroup->mScale;
+      groupData->mFollowingGroup.mResidualOffset =
+          currentGroup->mResidualOffset;
+      groupData->mFollowingGroup.mVisibleRect = currentGroup->mVisibleRect;
+      groupData->mFollowingGroup.mPreservedRect =
+          groupData->mFollowingGroup.mVisibleRect
+              .Intersect(groupData->mFollowingGroup.mLastVisibleRect)
+              .ToUnknownRect();
+      groupData->mFollowingGroup.mActualBounds = IntRect();
+
+      currentGroup->EndGroup(aCommandBuilder->mManager, aDisplayListBuilder,
+                             aBuilder, aResources, this, startOfCurrentGroup,
+                             item);
+
+      {
+        auto spaceAndClipChain = mClipManager.SwitchItem(item);
+        wr::SpaceAndClipChainHelper saccHelper(aBuilder, spaceAndClipChain);
+
+        sIndent++;
+        // Note: this call to CreateWebRenderCommands can recurse back into
+        // this function.
+        bool createdWRCommands = item->CreateWebRenderCommands(
+            aBuilder, aResources, aSc, manager, mDisplayListBuilder);
+        sIndent--;
+        MOZ_RELEASE_ASSERT(
+            createdWRCommands,
+            "active transforms should always succeed at creating "
+            "WebRender commands");
+      }
+
+      currentGroup = &groupData->mFollowingGroup;
+
+      startOfCurrentGroup = item->GetAbove();
+    } else {  // inactive item
+      ConstructItemInsideInactive(aCommandBuilder, aBuilder, aResources,
+                                  currentGroup, item, aSc);
+    }
+
+    item = item->GetAbove();
+  }
+
+  currentGroup->EndGroup(aCommandBuilder->mManager, aDisplayListBuilder,
+                         aBuilder, aResources, this, startOfCurrentGroup,
+                         nullptr);
+}
+
+// This does a pass over the display lists and will join the display items
+// into a single group.
+void Grouper::ConstructGroupInsideInactive(
+    WebRenderCommandBuilder* aCommandBuilder, wr::DisplayListBuilder& aBuilder,
+    wr::IpcResourceUpdateQueue& aResources, DIGroup* aGroup,
+    nsDisplayList* aList, const StackingContextHelper& aSc) {
+  nsDisplayItem* item = aList->GetBottom();
+  while (item) {
+    ConstructItemInsideInactive(aCommandBuilder, aBuilder, aResources, aGroup,
+                                item, aSc);
+    item = item->GetAbove();
+  }
+}
+
+bool BuildLayer(nsDisplayItem* aItem, BlobItemData* aData,
+                nsDisplayListBuilder* aDisplayListBuilder,
+                const gfx::Size& aScale);
+
+void Grouper::ConstructItemInsideInactive(
+    WebRenderCommandBuilder* aCommandBuilder, wr::DisplayListBuilder& aBuilder,
+    wr::IpcResourceUpdateQueue& aResources, DIGroup* aGroup,
+    nsDisplayItem* aItem, const StackingContextHelper& aSc) {
+  nsDisplayList* children = aItem->GetChildren();
+  BlobItemData* data = GetBlobItemDataForGroup(aItem, aGroup);
+
+  /* mInvalid unfortunately persists across paints. Clear it so that if we don't
+   * set it to 'true' we ensure that we're not using the value from the last
+   * time that we painted */
+  data->mInvalid = false;
+
+  // we compute the geometry change here because we have the transform around
+  // still
+  aGroup->ComputeGeometryChange(aItem, data, mTransform, mDisplayListBuilder);
+
+  // Temporarily restrict the image bounds to the bounds of the container so
+  // that clipped children within the container know about the clip. This
+  // ensures that the bounds passed to FlushItem are contained in the bounds of
+  // the clip so that we don't include items in the recording without including
+  // their corresponding clipping items.
+  IntRect oldClippedImageBounds = aGroup->mClippedImageBounds;
+  aGroup->mClippedImageBounds =
+      aGroup->mClippedImageBounds.Intersect(data->mRect);
+
+  if (aItem->GetType() == DisplayItemType::TYPE_FILTER) {
+    gfx::Size scale(1, 1);
+    // If ComputeDifferences finds any change, we invalidate the entire
+    // container item. This is needed because blob merging requires the entire
+    // item to be within the invalid region.
+    if (BuildLayer(aItem, data, mDisplayListBuilder, scale)) {
+      data->mInvalid = true;
+      aGroup->InvalidateRect(data->mRect);
+    }
+  } else if (aItem->GetType() == DisplayItemType::TYPE_TRANSFORM) {
+    nsDisplayTransform* transformItem = static_cast<nsDisplayTransform*>(aItem);
+    const Matrix4x4Flagged& t = transformItem->GetTransform();
+    Matrix t2d;
+    bool is2D = t.Is2D(&t2d);
+    if (!is2D) {
+      // We'll use BasicLayerManager to handle 3d transforms.
+      gfx::Size scale(1, 1);
+      // If ComputeDifferences finds any change, we invalidate the entire
+      // container item. This is needed because blob merging requires the entire
+      // item to be within the invalid region.
+      if (BuildLayer(aItem, data, mDisplayListBuilder, scale)) {
+        data->mInvalid = true;
+        aGroup->InvalidateRect(data->mRect);
+      }
+    } else {
+      Matrix m = mTransform;
+
+      GP("t2d: %f %f\n", t2d._31, t2d._32);
+      mTransform.PreMultiply(t2d);
+      GP("mTransform: %f %f\n", mTransform._31, mTransform._32);
+      ConstructGroupInsideInactive(aCommandBuilder, aBuilder, aResources,
+                                   aGroup, children, aSc);
+
+      mTransform = m;
+    }
+  } else if (children) {
+    sIndent++;
+    ConstructGroupInsideInactive(aCommandBuilder, aBuilder, aResources, aGroup,
+                                 children, aSc);
+    sIndent--;
+  }
+
+  GP("Including %s of %d\n", aItem->Name(), aGroup->mDisplayItems.Count());
+  aGroup->mClippedImageBounds = oldClippedImageBounds;
+}
+
+/* This is just a copy of nsRect::ScaleToOutsidePixels with an offset added in.
+ * The offset is applied just before the rounding. It's in the scaled space. */
+static mozilla::LayerIntRect ScaleToOutsidePixelsOffset(
+    nsRect aRect, float aXScale, float aYScale, nscoord aAppUnitsPerPixel,
+    LayerPoint aOffset) {
+  mozilla::LayerIntRect rect;
+  rect.SetNonEmptyBox(
+      NSToIntFloor(NSAppUnitsToFloatPixels(aRect.x, float(aAppUnitsPerPixel)) *
+                       aXScale +
+                   aOffset.x),
+      NSToIntFloor(NSAppUnitsToFloatPixels(aRect.y, float(aAppUnitsPerPixel)) *
+                       aYScale +
+                   aOffset.y),
+      NSToIntCeil(
+          NSAppUnitsToFloatPixels(aRect.XMost(), float(aAppUnitsPerPixel)) *
+              aXScale +
+          aOffset.x),
+      NSToIntCeil(
+          NSAppUnitsToFloatPixels(aRect.YMost(), float(aAppUnitsPerPixel)) *
+              aYScale +
+          aOffset.y));
+  return rect;
+}
+
+/* This function is the same as the above except that it rounds to the
+ * nearest instead of rounding out. We use it for attempting to compute the
+ * actual pixel bounds of opaque items */
+static mozilla::gfx::IntRect ScaleToNearestPixelsOffset(
+    nsRect aRect, float aXScale, float aYScale, nscoord aAppUnitsPerPixel,
+    LayerPoint aOffset) {
+  mozilla::gfx::IntRect rect;
+  rect.SetNonEmptyBox(
+      NSToIntFloor(NSAppUnitsToFloatPixels(aRect.x, float(aAppUnitsPerPixel)) *
+                       aXScale +
+                   aOffset.x + 0.5),
+      NSToIntFloor(NSAppUnitsToFloatPixels(aRect.y, float(aAppUnitsPerPixel)) *
+                       aYScale +
+                   aOffset.y + 0.5),
+      NSToIntFloor(
+          NSAppUnitsToFloatPixels(aRect.XMost(), float(aAppUnitsPerPixel)) *
+              aXScale +
+          aOffset.x + 0.5),
+      NSToIntFloor(
+          NSAppUnitsToFloatPixels(aRect.YMost(), float(aAppUnitsPerPixel)) *
+              aYScale +
+          aOffset.y + 0.5));
+  return rect;
+}
+
+RenderRootStateManager* WebRenderCommandBuilder::GetRenderRootStateManager() {
+  return mManager->GetRenderRootStateManager();
+}
+
+void WebRenderCommandBuilder::DoGroupingForDisplayList(
+    nsDisplayList* aList, nsDisplayItem* aWrappingItem,
+    nsDisplayListBuilder* aDisplayListBuilder, const StackingContextHelper& aSc,
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources) {
+  if (!aList->GetBottom()) {
+    return;
+  }
+
+  GP("DoGroupingForDisplayList\n");
+
+  mClipManager.BeginList(aSc);
+  Grouper g(mClipManager);
+
+  int32_t appUnitsPerDevPixel =
+      aWrappingItem->Frame()->PresContext()->AppUnitsPerDevPixel();
+
+  g.mDisplayListBuilder = aDisplayListBuilder;
+  RefPtr<WebRenderGroupData> groupData =
+      CreateOrRecycleWebRenderUserData<WebRenderGroupData>(aWrappingItem);
+
+  bool snapped;
+  nsRect groupBounds =
+      aWrappingItem->GetUntransformedBounds(aDisplayListBuilder, &snapped);
+  DIGroup& group = groupData->mSubGroup;
+
+  gfx::Size scale = aSc.GetInheritedScale();
+  GP("Inherrited scale %f %f\n", scale.width, scale.height);
+
+  auto trans =
+      ViewAs<LayerPixel>(aSc.GetSnappingSurfaceTransform().GetTranslation());
+  auto snappedTrans = LayerIntPoint::Floor(trans);
+  LayerPoint residualOffset = trans - snappedTrans;
+
+  auto p = group.mGroupBounds;
+  auto q = groupBounds;
+  // XXX: we currently compute the paintRect for the entire svg, but if the svg
+  // gets split into multiple groups (blobs), then they will all inherit this
+  // overall size even though they may each be much smaller. This can lead to
+  // allocating much larger textures than necessary in webrender.
+  //
+  // Don't bother fixing this unless we run into this in the real world, though.
+  auto layerBounds =
+      ScaleToOutsidePixelsOffset(groupBounds, scale.width, scale.height,
+                                 appUnitsPerDevPixel, residualOffset);
+
+  const nsRect& untransformedPaintRect =
+      aWrappingItem->GetUntransformedPaintRect();
+
+  auto visibleRect = ScaleToOutsidePixelsOffset(
+                         untransformedPaintRect, scale.width, scale.height,
+                         appUnitsPerDevPixel, residualOffset)
+                         .Intersect(layerBounds);
+
+  GP("LayerBounds: %d %d %d %d\n", layerBounds.x, layerBounds.y,
+     layerBounds.width, layerBounds.height);
+  GP("VisibleRect: %d %d %d %d\n", visibleRect.x, visibleRect.y,
+     visibleRect.width, visibleRect.height);
+
+  GP("Inherrited scale %f %f\n", scale.width, scale.height);
+  GP("Bounds: %d %d %d %d vs %d %d %d %d\n", p.x, p.y, p.width, p.height, q.x,
+     q.y, q.width, q.height);
+
+  group.mInvalidRect.SetEmpty();
+  if (group.mAppUnitsPerDevPixel != appUnitsPerDevPixel ||
+      group.mScale != scale || group.mResidualOffset != residualOffset) {
+    GP("Property change. Deleting blob\n");
+
+    if (group.mAppUnitsPerDevPixel != appUnitsPerDevPixel) {
+      GP(" App unit change %d -> %d\n", group.mAppUnitsPerDevPixel,
+         appUnitsPerDevPixel);
+    }
+    // The bounds have changed so we need to discard the old image and add all
+    // the commands again.
+    auto p = group.mGroupBounds;
+    auto q = groupBounds;
+    if (!group.mGroupBounds.IsEqualEdges(groupBounds)) {
+      GP(" Bounds change: %d %d %d %d -> %d %d %d %d\n", p.x, p.y, p.width,
+         p.height, q.x, q.y, q.width, q.height);
+    }
+
+    if (group.mScale != scale) {
+      GP(" Scale %f %f -> %f %f\n", group.mScale.width, group.mScale.height,
+         scale.width, scale.height);
+    }
+
+    if (group.mResidualOffset != residualOffset) {
+      GP(" Residual Offset %f %f -> %f %f\n", group.mResidualOffset.x,
+         group.mResidualOffset.y, residualOffset.x, residualOffset.y);
+    }
+
+    group.ClearItems();
+    group.ClearImageKey(mManager->GetRenderRootStateManager());
+  }
+
+  ScrollableLayerGuid::ViewID scrollId = ScrollableLayerGuid::NULL_SCROLL_ID;
+  if (const ActiveScrolledRoot* asr = aWrappingItem->GetActiveScrolledRoot()) {
+    scrollId = asr->GetViewId();
+  }
+
+  g.mAppUnitsPerDevPixel = appUnitsPerDevPixel;
+  group.mResidualOffset = residualOffset;
+  group.mGroupBounds = groupBounds;
+  group.mLayerBounds = layerBounds;
+  group.mVisibleRect = visibleRect;
+  group.mActualBounds = IntRect();
+  group.mPreservedRect =
+      group.mVisibleRect.Intersect(group.mLastVisibleRect).ToUnknownRect();
+  group.mAppUnitsPerDevPixel = appUnitsPerDevPixel;
+  group.mClippedImageBounds = layerBounds.ToUnknownRect();
+
+  g.mTransform = Matrix::Scaling(scale.width, scale.height)
+                     .PostTranslate(residualOffset.x, residualOffset.y);
+  group.mScale = scale;
+  group.mScrollId = scrollId;
+  g.ConstructGroups(aDisplayListBuilder, this, aBuilder, aResources, &group,
+                    aList, aSc);
+  mClipManager.EndList(aSc);
+}
+
+WebRenderCommandBuilder::WebRenderCommandBuilder(
+    WebRenderLayerManager* aManager)
+    : mManager(aManager),
+      mLastAsr(nullptr),
+      mBuilderDumpIndex(0),
+      mDumpIndent(0),
+      mDoGrouping(false),
+      mContainsSVGGroup(false) {}
+
+void WebRenderCommandBuilder::Destroy() {
+  mLastCanvasDatas.Clear();
+  mLastLocalCanvasDatas.Clear();
+  ClearCachedResources();
+}
+
+void WebRenderCommandBuilder::EmptyTransaction() {
+  // We need to update canvases that might have changed.
+  for (auto iter = mLastCanvasDatas.Iter(); !iter.Done(); iter.Next()) {
+    RefPtr<WebRenderCanvasData> canvasData = iter.Get()->GetKey();
+    WebRenderCanvasRendererAsync* canvas = canvasData->GetCanvasRenderer();
+    if (canvas) {
+      canvas->UpdateCompositableClientForEmptyTransaction();
+    }
+  }
+  for (auto iter = mLastLocalCanvasDatas.Iter(); !iter.Done(); iter.Next()) {
+    RefPtr<WebRenderLocalCanvasData> canvasData = iter.Get()->GetKey();
+    canvasData->RefreshExternalImage();
+    canvasData->RequestFrameReadback();
+  }
+}
+
+bool WebRenderCommandBuilder::NeedsEmptyTransaction() {
+  return !mLastCanvasDatas.IsEmpty() || !mLastLocalCanvasDatas.IsEmpty();
+}
+
+void WebRenderCommandBuilder::BuildWebRenderCommands(
+    wr::DisplayListBuilder& aBuilder,
+    wr::IpcResourceUpdateQueue& aResourceUpdates, nsDisplayList* aDisplayList,
+    nsDisplayListBuilder* aDisplayListBuilder, WebRenderScrollData& aScrollData,
+    WrFiltersHolder&& aFilters) {
+  AUTO_PROFILER_LABEL_CATEGORY_PAIR(GRAPHICS_WRDisplayList);
+
+  StackingContextHelper sc;
+  aScrollData = WebRenderScrollData(mManager, aDisplayListBuilder);
+  MOZ_ASSERT(mLayerScrollData.empty());
+  mClipManager.BeginBuild(mManager, aBuilder);
+  mBuilderDumpIndex = 0;
+  mLastCanvasDatas.Clear();
+  mLastLocalCanvasDatas.Clear();
+  mLastAsr = nullptr;
+  mContainsSVGGroup = false;
+  MOZ_ASSERT(mDumpIndent == 0);
+
+  {
+    wr::StackingContextParams params;
+    params.mFilters = std::move(aFilters.filters);
+    params.mFilterDatas = std::move(aFilters.filter_datas);
+    params.clip =
+        wr::WrStackingContextClip::ClipChain(aBuilder.CurrentClipChainId());
+
+    StackingContextHelper pageRootSc(sc, nullptr, nullptr, nullptr, aBuilder,
+                                     params);
+    if (ShouldDumpDisplayList(aDisplayListBuilder)) {
+      mBuilderDumpIndex =
+          aBuilder.Dump(mDumpIndent + 1, Some(mBuilderDumpIndex), Nothing());
+    }
+    CreateWebRenderCommandsFromDisplayList(aDisplayList, nullptr,
+                                           aDisplayListBuilder, pageRootSc,
+                                           aBuilder, aResourceUpdates);
+  }
+
+  // Make a "root" layer data that has everything else as descendants
+  mLayerScrollData.emplace_back();
+  mLayerScrollData.back().InitializeRoot(mLayerScrollData.size() - 1);
+  auto callback =
+      [&aScrollData](ScrollableLayerGuid::ViewID aScrollId) -> bool {
+    return aScrollData.HasMetadataFor(aScrollId).isSome();
+  };
+  Maybe<ScrollMetadata> rootMetadata = nsLayoutUtils::GetRootMetadata(
+      aDisplayListBuilder, mManager, ContainerLayerParameters(), callback);
+  if (rootMetadata) {
+    // Put the fallback root metadata on the rootmost layer that is
+    // a matching async zoom container, or the root layer that we just
+    // created above.
+    size_t rootMetadataTarget = mLayerScrollData.size() - 1;
+    for (size_t i = rootMetadataTarget; i > 0; i--) {
+      if (auto zoomContainerId =
+              mLayerScrollData[i - 1].GetAsyncZoomContainerId()) {
+        if (*zoomContainerId == rootMetadata->GetMetrics().GetScrollId()) {
+          rootMetadataTarget = i - 1;
+          break;
+        }
+      }
+    }
+    mLayerScrollData[rootMetadataTarget].AppendScrollMetadata(
+        aScrollData, rootMetadata.ref());
+  }
+
+  // Append the WebRenderLayerScrollData items into WebRenderScrollData
+  // in reverse order, from topmost to bottommost. This is in keeping with
+  // the semantics of WebRenderScrollData.
+  for (auto it = mLayerScrollData.crbegin(); it != mLayerScrollData.crend();
+       it++) {
+    aScrollData.AddLayerData(*it);
+  }
+  mLayerScrollData.clear();
+  mClipManager.EndBuild();
+
+  // Remove the user data those are not displayed on the screen and
+  // also reset the data to unused for next transaction.
+  RemoveUnusedAndResetWebRenderUserData();
+}
+
+bool WebRenderCommandBuilder::ShouldDumpDisplayList(
+    nsDisplayListBuilder* aBuilder) {
+  return aBuilder && aBuilder->IsInActiveDocShell() &&
+         ((XRE_IsParentProcess() &&
+           StaticPrefs::gfx_webrender_dl_dump_parent()) ||
+          (XRE_IsContentProcess() &&
+           StaticPrefs::gfx_webrender_dl_dump_content()));
+}
+
+void WebRenderCommandBuilder::CreateWebRenderCommands(
+    nsDisplayItem* aItem, mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  auto* item = aItem->AsPaintedDisplayItem();
+  MOZ_RELEASE_ASSERT(item, "Tried to paint item that cannot be painted");
+
+  if (aBuilder.ReuseItem(item)) {
+    // No further processing should be needed, since the item was reused.
+    return;
+  }
+
+  aItem->SetPaintRect(aItem->GetBuildingRect());
+  RenderRootStateManager* manager = mManager->GetRenderRootStateManager();
+
+  // Note: this call to CreateWebRenderCommands can recurse back into
+  // this function if the |item| is a wrapper for a sublist.
+  const bool createdWRCommands = aItem->CreateWebRenderCommands(
+      aBuilder, aResources, aSc, manager, aDisplayListBuilder);
+
+  if (!createdWRCommands) {
+    PushItemAsImage(aItem, aBuilder, aResources, aSc, aDisplayListBuilder);
+  }
+}
+
+void WebRenderCommandBuilder::CreateWebRenderCommandsFromDisplayList(
+    nsDisplayList* aDisplayList, nsDisplayItem* aWrappingItem,
+    nsDisplayListBuilder* aDisplayListBuilder, const StackingContextHelper& aSc,
+    wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources) {
+  if (mDoGrouping) {
+    MOZ_RELEASE_ASSERT(
+        aWrappingItem,
+        "Only the root list should have a null wrapping item, and mDoGrouping "
+        "should never be true for the root list.");
+    GP("actually entering the grouping code\n");
+    DoGroupingForDisplayList(aDisplayList, aWrappingItem, aDisplayListBuilder,
+                             aSc, aBuilder, aResources);
+    return;
+  }
+
+  bool dumpEnabled = ShouldDumpDisplayList(aDisplayListBuilder);
+  if (dumpEnabled) {
+    // If we're inside a nested display list, print the WR DL items from the
+    // wrapper item before we start processing the nested items.
+    mBuilderDumpIndex =
+        aBuilder.Dump(mDumpIndent + 1, Some(mBuilderDumpIndex), Nothing());
+  }
+
+  mDumpIndent++;
+  mClipManager.BeginList(aSc);
+
+  bool apzEnabled = mManager->AsyncPanZoomEnabled();
+
+  FlattenedDisplayListIterator iter(aDisplayListBuilder, aDisplayList);
+  while (iter.HasNext()) {
+    nsDisplayItem* item = iter.GetNextItem();
+
+    DisplayItemType itemType = item->GetType();
+
+    // If this is an unscrolled background color item, in the root display list
+    // for the parent process, consider doing opaque checks.
+    if (XRE_IsParentProcess() && !aWrappingItem &&
+        itemType == DisplayItemType::TYPE_BACKGROUND_COLOR &&
+        !item->GetActiveScrolledRoot() &&
+        item->GetClip().GetRoundedRectCount() == 0) {
+      bool snap;
+      nsRegion opaque = item->GetOpaqueRegion(aDisplayListBuilder, &snap);
+      if (opaque.GetNumRects() == 1) {
+        nsRect clippedOpaque =
+            item->GetClip().ApplyNonRoundedIntersection(opaque.GetBounds());
+        if (!clippedOpaque.IsEmpty()) {
+          aDisplayListBuilder->AddWindowOpaqueRegion(item->Frame(),
+                                                     clippedOpaque);
+        }
+      }
+    }
+
+    bool forceNewLayerData = false;
+    size_t layerCountBeforeRecursing = mLayerScrollData.size();
+    if (apzEnabled) {
+      // For some types of display items we want to force a new
+      // WebRenderLayerScrollData object, to ensure we preserve the APZ-relevant
+      // data that is in the display item.
+      forceNewLayerData = item->UpdateScrollData(nullptr, nullptr);
+
+      // Anytime the ASR changes we also want to force a new layer data because
+      // the stack of scroll metadata is going to be different for this
+      // display item than previously, so we can't squash the display items
+      // into the same "layer".
+      const ActiveScrolledRoot* asr = item->GetActiveScrolledRoot();
+      if (asr != mLastAsr) {
+        mLastAsr = asr;
+        forceNewLayerData = true;
+      }
+
+      // Refer to the comment on StackingContextHelper::mDeferredTransformItem
+      // for an overview of what this is about. This bit of code applies to the
+      // case where we are deferring a transform item, and we then need to defer
+      // another transform with a different ASR. In such a case we cannot just
+      // merge the deferred transforms, but need to force a new
+      // WebRenderLayerScrollData item to flush the old deferred transform, so
+      // that we can then start deferring the new one.
+      if (!forceNewLayerData &&
+          item->GetType() == DisplayItemType::TYPE_TRANSFORM &&
+          aSc.GetDeferredTransformItem() &&
+          (*aSc.GetDeferredTransformItem())->GetActiveScrolledRoot() != asr) {
+        forceNewLayerData = true;
+      }
+
+      // If we're going to create a new layer data for this item, stash the
+      // ASR so that if we recurse into a sublist they will know where to stop
+      // walking up their ASR chain when building scroll metadata.
+      if (forceNewLayerData) {
+        mAsrStack.push_back(asr);
+      }
+    }
+
+    // This is where we emulate the clip/scroll stack that was previously
+    // implemented on the WR display list side.
+    auto spaceAndClipChain = mClipManager.SwitchItem(item);
+    wr::SpaceAndClipChainHelper saccHelper(aBuilder, spaceAndClipChain);
+
+    {  // scope restoreDoGrouping
+      AutoRestore<bool> restoreDoGrouping(mDoGrouping);
+      if (itemType == DisplayItemType::TYPE_SVG_WRAPPER) {
+        // Inside an <svg>, all display items that are not LAYER_ACTIVE wrapper
+        // display items (like animated transforms / opacity) share the same
+        // animated geometry root, so we can combine subsequent items of that
+        // type into the same image.
+        mContainsSVGGroup = mDoGrouping = true;
+        GP("attempting to enter the grouping code\n");
+      }
+
+      if (dumpEnabled) {
+        std::stringstream ss;
+        nsIFrame::PrintDisplayItem(aDisplayListBuilder, item, ss,
+                                   static_cast<uint32_t>(mDumpIndent));
+        printf_stderr("%s", ss.str().c_str());
+      }
+
+      CreateWebRenderCommands(item, aBuilder, aResources, aSc,
+                              aDisplayListBuilder);
+
+      if (dumpEnabled) {
+        mBuilderDumpIndex =
+            aBuilder.Dump(mDumpIndent + 1, Some(mBuilderDumpIndex), Nothing());
+      }
+    }
+
+    if (apzEnabled) {
+      if (forceNewLayerData) {
+        // Pop the thing we pushed before the recursion, so the topmost item on
+        // the stack is enclosing display item's ASR (or the stack is empty)
+        mAsrStack.pop_back();
+        const ActiveScrolledRoot* stopAtAsr =
+            mAsrStack.empty() ? nullptr : mAsrStack.back();
+
+        int32_t descendants =
+            mLayerScrollData.size() - layerCountBeforeRecursing;
+
+        // See the comments on StackingContextHelper::mDeferredTransformItem
+        // for an overview of what deferred transforms are.
+        // In the case where we deferred a transform, but have a child display
+        // item with a different ASR than the deferred transform item, we cannot
+        // put the transform on the WebRenderLayerScrollData item for the child.
+        // We cannot do this because it will not conform to APZ's expectations
+        // with respect to how the APZ tree ends up structured. In particular,
+        // the GetTransformToThis() for the child APZ (which is created for the
+        // child item's ASR) will not include the transform when we actually do
+        // want it to.
+        // When we run into this scenario, we solve it by creating two
+        // WebRenderLayerScrollData items; one that just holds the transform,
+        // that we deferred, and a child WebRenderLayerScrollData item that
+        // holds the scroll metadata for the child's ASR.
+        Maybe<nsDisplayTransform*> deferred = aSc.GetDeferredTransformItem();
+        if (deferred && (*deferred)->GetActiveScrolledRoot() !=
+                            item->GetActiveScrolledRoot()) {
+          // This creates the child WebRenderLayerScrollData for |item|, but
+          // omits the transform (hence the Nothing() as the last argument to
+          // Initialize(...)). We also need to make sure that the ASR from
+          // the deferred transform item is not on this node, so we use that
+          // ASR as the "stop at" ASR for this WebRenderLayerScrollData.
+          mLayerScrollData.emplace_back();
+          mLayerScrollData.back().Initialize(
+              mManager->GetScrollData(), item, descendants,
+              (*deferred)->GetActiveScrolledRoot(), Nothing());
+
+          // The above WebRenderLayerScrollData will also be a descendant of
+          // the transform-holding WebRenderLayerScrollData we create below.
+          descendants++;
+
+          // This creates the WebRenderLayerScrollData for the deferred
+          // transform item. This holds the transform matrix and the remaining
+          // ASRs needed to complete the ASR chain (i.e. the ones from the
+          // stopAtAsr down to the deferred transform item's ASR, which must be
+          // "between" stopAtAsr and |item|'s ASR in the ASR tree).
+          mLayerScrollData.emplace_back();
+          mLayerScrollData.back().Initialize(mManager->GetScrollData(),
+                                             *deferred, descendants, stopAtAsr,
+                                             aSc.GetDeferredTransformMatrix());
+        } else {
+          // This is the "simple" case where we don't need to create two
+          // WebRenderLayerScrollData items; we can just create one that also
+          // holds the deferred transform matrix, if any.
+          mLayerScrollData.emplace_back();
+          mLayerScrollData.back().Initialize(mManager->GetScrollData(), item,
+                                             descendants, stopAtAsr,
+                                             aSc.GetDeferredTransformMatrix());
+        }
+      }
+    }
+  }
+
+  mDumpIndent--;
+  mClipManager.EndList(aSc);
+}
+
+void WebRenderCommandBuilder::PushOverrideForASR(
+    const ActiveScrolledRoot* aASR, const wr::WrSpatialId& aSpatialId) {
+  mClipManager.PushOverrideForASR(aASR, aSpatialId);
+}
+
+void WebRenderCommandBuilder::PopOverrideForASR(
+    const ActiveScrolledRoot* aASR) {
+  mClipManager.PopOverrideForASR(aASR);
+}
+
+Maybe<wr::ImageKey> WebRenderCommandBuilder::CreateImageKey(
+    nsDisplayItem* aItem, ImageContainer* aContainer,
+    mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    mozilla::wr::ImageRendering aRendering, const StackingContextHelper& aSc,
+    gfx::IntSize& aSize, const Maybe<LayoutDeviceRect>& aAsyncImageBounds) {
+  RefPtr<WebRenderImageData> imageData =
+      CreateOrRecycleWebRenderUserData<WebRenderImageData>(aItem);
+  MOZ_ASSERT(imageData);
+
+  if (aContainer->IsAsync()) {
+    MOZ_ASSERT(aAsyncImageBounds);
+
+    LayoutDeviceRect rect = aAsyncImageBounds.value();
+    LayoutDeviceRect scBounds(LayoutDevicePoint(0, 0), rect.Size());
+    // TODO!
+    // We appear to be using the image bridge for a lot (most/all?) of
+    // layers-free image handling and that breaks frame consistency.
+    imageData->CreateAsyncImageWebRenderCommands(
+        aBuilder, aContainer, aSc, rect, scBounds, aContainer->GetRotation(),
+        aRendering, wr::MixBlendMode::Normal, !aItem->BackfaceIsHidden());
+    return Nothing();
+  }
+
+  AutoLockImage autoLock(aContainer);
+  if (!autoLock.HasImage()) {
+    return Nothing();
+  }
+  mozilla::layers::Image* image = autoLock.GetImage();
+  aSize = image->GetSize();
+
+  return imageData->UpdateImageKey(aContainer, aResources);
+}
+
+bool WebRenderCommandBuilder::PushImage(
+    nsDisplayItem* aItem, ImageContainer* aContainer,
+    mozilla::wr::DisplayListBuilder& aBuilder,
+    mozilla::wr::IpcResourceUpdateQueue& aResources,
+    const StackingContextHelper& aSc, const LayoutDeviceRect& aRect,
+    const LayoutDeviceRect& aClip) {
+  mozilla::wr::ImageRendering rendering = wr::ToImageRendering(
+      nsLayoutUtils::GetSamplingFilterForFrame(aItem->Frame()));
+  gfx::IntSize size;
+  Maybe<wr::ImageKey> key =
+      CreateImageKey(aItem, aContainer, aBuilder, aResources, rendering, aSc,
+                     size, Some(aRect));
+  if (aContainer->IsAsync()) {
+    // Async ImageContainer does not create ImageKey, instead it uses Pipeline.
+    MOZ_ASSERT(key.isNothing());
+    return true;
+  }
+  if (!key) {
+    return false;
+  }
+
+  auto r = wr::ToLayoutRect(aRect);
+  auto c = wr::ToLayoutRect(aClip);
+  aBuilder.PushImage(r, c, !aItem->BackfaceIsHidden(), rendering, key.value());
+
+  return true;
+}
+
+bool BuildLayer(nsDisplayItem* aItem, BlobItemData* aData,
+                nsDisplayListBuilder* aDisplayListBuilder,
+                const gfx::Size& aScale) {
+  if (!aData->mLayerManager) {
+    aData->mLayerManager =
+        new BasicLayerManager(BasicLayerManager::BLM_INACTIVE);
+  }
+  RefPtr<BasicLayerManager> blm = aData->mLayerManager;
+  UniquePtr<LayerProperties> props;
+  if (blm->GetRoot()) {
+    props = LayerProperties::CloneFrom(blm->GetRoot());
+  }
+  FrameLayerBuilder* layerBuilder = new FrameLayerBuilder();
+  layerBuilder->Init(aDisplayListBuilder, blm, nullptr, true);
+  layerBuilder->DidBeginRetainedLayerTransaction(blm);
+
+  blm->BeginTransaction();
+  bool isInvalidated = false;
+
+  ContainerLayerParameters param(aScale.width, aScale.height);
+  RefPtr<Layer> root = aItem->AsPaintedDisplayItem()->BuildLayer(
+      aDisplayListBuilder, blm, param);
+
+  if (root) {
+    blm->SetRoot(root);
+    layerBuilder->WillEndTransaction();
+
+    // Check if there is any invalidation region.
+    nsIntRegion invalid;
+    if (props) {
+      props->ComputeDifferences(root, invalid, nullptr);
+      if (!invalid.IsEmpty()) {
+        isInvalidated = true;
+      }
+    } else {
+      isInvalidated = true;
+    }
+  }
+  blm->AbortTransaction();
+
+  return isInvalidated;
+}
+
+static bool PaintByLayer(nsDisplayItem* aItem,
+                         nsDisplayListBuilder* aDisplayListBuilder,
+                         const RefPtr<BasicLayerManager>& aManager,
+                         gfxContext* aContext, const gfx::Size& aScale,
+                         const std::function<void()>& aPaintFunc) {
+  UniquePtr<LayerProperties> props;
+  if (aManager->GetRoot()) {
+    props = LayerProperties::CloneFrom(aManager->GetRoot());
+  }
+  FrameLayerBuilder* layerBuilder = new FrameLayerBuilder();
+  layerBuilder->Init(aDisplayListBuilder, aManager, nullptr, true);
+  layerBuilder->DidBeginRetainedLayerTransaction(aManager);
+
+  aManager->SetDefaultTarget(aContext);
+  nsCString none;
+  aManager->BeginTransactionWithTarget(aContext, none);
+  bool isInvalidated = false;
+
+  ContainerLayerParameters param(aScale.width, aScale.height);
+  RefPtr<Layer> root = aItem->AsPaintedDisplayItem()->BuildLayer(
+      aDisplayListBuilder, aManager, param);
+
+  if (root) {
+    aManager->SetRoot(root);
+    layerBuilder->WillEndTransaction();
+
+    aPaintFunc();
+
+    // Check if there is any invalidation region.
+    nsIntRegion invalid;
+    if (props) {
+      props->ComputeDifferences(root, invalid, nullptr);
+      if (!invalid.IsEmpty()) {
+        isInvalidated = true;
+      }
+    } else {
+      isInvalidated = true;
+    }
+  }
+
+#ifdef MOZ_DUMP_PAINTING
+  if (gfxUtils::DumpDisplayList() || gfxEnv::DumpPaint()) {
+    fprintf_stderr(
+        gfxUtils::sDumpPaintFile,
+        "Basic layer tree for painting contents of display item %s(%p):\n",
+        aItem->Name(), aItem->Frame());
+    std::stringstream stream;
+    aManager->Dump(stream, "", gfxEnv::DumpPaintToFile());
+    fprint_stderr(gfxUtils::sDumpPaintFile,
+                  stream);  // not a typo, fprint_stderr declared in nsDebug.h
+  }
+#endif
+
+  if (aManager->InTransaction()) {
+    aManager->AbortTransaction();
+  }
+
+  aManager->SetTarget(nullptr);
+  aManager->SetDefaultTarget(nullptr);
+
+  return isInvalidated;
+}
+
+static bool PaintItemByDrawTarget(nsDisplayItem* aItem, gfx::DrawTarget* aDT,
+                                  const LayoutDevicePoint& aOffset,
+                                  const IntRect& visibleRect,
+                                  nsDisplayListBuilder* aDisplayListBuilder,
+                                  const RefPtr<BasicLayerManager>& aManager,
+                                  const gfx::Size& aScale,
+                                  Maybe<gfx::DeviceColor>& aHighlight) {
+  MOZ_ASSERT(aDT);
+
+  bool isInvalidated = false;
+  // XXX Why is this ClearRect() needed?
+  aDT->ClearRect(Rect(visibleRect));
+  RefPtr<gfxContext> context = gfxContext::CreateOrNull(aDT);
+  MOZ_ASSERT(context);
+
+  switch (aItem->GetType()) {
+    case DisplayItemType::TYPE_SVG_WRAPPER:
+    case DisplayItemType::TYPE_MASK: {
+      // These items should be handled by other code paths
+      MOZ_RELEASE_ASSERT(0);
+      break;
+    }
+    case DisplayItemType::TYPE_FILTER: {
+      context->SetMatrix(context->CurrentMatrix()
+                             .PreScale(aScale.width, aScale.height)
+                             .PreTranslate(-aOffset.x, -aOffset.y));
+      isInvalidated = PaintByLayer(
+          aItem, aDisplayListBuilder, aManager, context, {1, 1}, [&]() {
+            static_cast<nsDisplayFilters*>(aItem)->PaintAsLayer(
+                aDisplayListBuilder, context, aManager);
+          });
+      break;
+    }
+
+    default:
+      if (!aItem->AsPaintedDisplayItem()) {
+        break;
+      }
+
+      context->SetMatrix(context->CurrentMatrix()
+                             .PreScale(aScale.width, aScale.height)
+                             .PreTranslate(-aOffset.x, -aOffset.y));
+      if (aDisplayListBuilder->IsPaintingToWindow()) {
+        aItem->Frame()->AddStateBits(NS_FRAME_PAINTED_THEBES);
+      }
+      aItem->AsPaintedDisplayItem()->Paint(aDisplayListBuilder, context);
+      isInvalidated = true;
+      break;
+  }
+
+  if (aItem->GetType() != DisplayItemType::TYPE_MASK) {
+    // Apply highlight fills, if the appropriate prefs are set.
+    // We don't do this for masks because we'd be filling the A8 mask surface,
+    // which isn't very useful.
+    if (aHighlight) {
+      aDT->SetTransform(gfx::Matrix());
+      aDT->FillRect(Rect(visibleRect), gfx::ColorPattern(aHighlight.value()));
+    }
+    if (aItem->Frame()->PresContext()->GetPaintFlashing() && isInvalidated) {
+      aDT->SetTransform(gfx::Matrix());
+      float r = float(rand()) / float(RAND_MAX);
+      float g = float(rand()) / float(RAND_MAX);
+      float b = float(rand()) / float(RAND_MAX);
+      aDT->FillRect(Rect(visibleRect),
+                    gfx::ColorPattern(gfx::DeviceColor(r, g, b, 0.5)));
+    }
+  }
+
+  return isInvalidated;
+}
+
+// When drawing fallback images we create either
+// a real image or a blob image that will contain the display item.
+// In the case of a blob image we paint the item at 0,0 instead
+// of trying to keep at aItem->GetBounds().TopLeft() like we do
+// with SVG. We do this because there's not necessarily a reference frame
+// between us and the rest of the world so the the coordinates
+// that we get for the bounds are not necessarily stable across scrolling
+// or other movement.
+already_AddRefed<WebRenderFallbackData>
+WebRenderCommandBuilder::GenerateFallbackData(
+    nsDisplayItem* aItem, wr::DisplayListBuilder& aBuilder,
+    wr::IpcResourceUpdateQueue& aResources, const StackingContextHelper& aSc,
+    nsDisplayListBuilder* aDisplayListBuilder, LayoutDeviceRect& aImageRect) {
+  const bool paintOnContentSide = aItem->MustPaintOnContentSide();
+  bool useBlobImage =
+      StaticPrefs::gfx_webrender_blob_images() && !paintOnContentSide;
+  Maybe<gfx::DeviceColor> highlight = Nothing();
+  if (StaticPrefs::gfx_webrender_highlight_painted_layers()) {
+    highlight = Some(useBlobImage ? gfx::DeviceColor(1.0, 0.0, 0.0, 0.5)
+                                  : gfx::DeviceColor(1.0, 1.0, 0.0, 0.5));
+  }
+
+  RefPtr<WebRenderFallbackData> fallbackData =
+      CreateOrRecycleWebRenderUserData<WebRenderFallbackData>(aItem);
+
+  bool snap;
+  nsRect itemBounds = aItem->GetBounds(aDisplayListBuilder, &snap);
+
+  // Blob images will only draw the visible area of the blob so we don't need to
+  // clip them here and can just rely on the webrender clipping.
+  // TODO We also don't clip native themed widget to avoid over-invalidation
+  // during scrolling. It would be better to support a sort of streaming/tiling
+  // scheme for large ones but the hope is that we should not have large native
+  // themed items.
+  nsRect paintBounds = (useBlobImage || paintOnContentSide)
+                           ? itemBounds
+                           : aItem->GetClippedBounds(aDisplayListBuilder);
+
+  // nsDisplayItem::Paint() may refer the variables that come from
+  // ComputeVisibility(). So we should call ComputeVisibility() before painting.
+  // e.g.: nsDisplayBoxShadowInner uses mPaintRect in Paint() and mPaintRect is
+  // computed in nsDisplayBoxShadowInner::ComputeVisibility().
+  nsRegion visibleRegion(paintBounds);
+  aItem->SetPaintRect(paintBounds);
+  aItem->ComputeVisibility(aDisplayListBuilder, &visibleRegion);
+
+  const int32_t appUnitsPerDevPixel =
+      aItem->Frame()->PresContext()->AppUnitsPerDevPixel();
+  auto bounds =
+      LayoutDeviceRect::FromAppUnits(paintBounds, appUnitsPerDevPixel);
+  if (bounds.IsEmpty()) {
+    return nullptr;
+  }
+
+  gfx::Size scale = aSc.GetInheritedScale();
+  gfx::Size oldScale = fallbackData->mScale;
+  // We tolerate slight changes in scale so that we don't, for example,
+  // rerasterize on MotionMark
+  bool differentScale = gfx::FuzzyEqual(scale.width, oldScale.width, 1e-6f) &&
+                        gfx::FuzzyEqual(scale.height, oldScale.height, 1e-6f);
+
+  LayoutDeviceToLayerScale2D layerScale(scale.width, scale.height);
+
+  auto trans =
+      ViewAs<LayerPixel>(aSc.GetSnappingSurfaceTransform().GetTranslation());
+  auto snappedTrans = LayerIntPoint::Floor(trans);
+  LayerPoint residualOffset = trans - snappedTrans;
+
+  nsRegion opaqueRegion = aItem->GetOpaqueRegion(aDisplayListBuilder, &snap);
+  wr::OpacityType opacity = opaqueRegion.Contains(paintBounds)
+                                ? wr::OpacityType::Opaque
+                                : wr::OpacityType::HasAlphaChannel;
+
+  LayerIntRect dtRect, visibleRect;
+  // If we think the item is opaque we round the bounds
+  // to the nearest pixel instead of rounding them out. If we rounded
+  // out we'd potentially introduce transparent pixels.
+  //
+  // Ideally we'd be able to ask an item its bounds in pixels and whether
+  // they're all opaque. Unfortunately no such API exists so we currently
+  // just hope that we get it right.
+  if (opacity == wr::OpacityType::Opaque && snap) {
+    dtRect = LayerIntRect::FromUnknownRect(
+        ScaleToNearestPixelsOffset(paintBounds, scale.width, scale.height,
+                                   appUnitsPerDevPixel, residualOffset));
+
+    visibleRect = LayerIntRect::FromUnknownRect(
+                      ScaleToNearestPixelsOffset(
+                          aItem->GetBuildingRect(), scale.width, scale.height,
+                          appUnitsPerDevPixel, residualOffset))
+                      .Intersect(dtRect);
+  } else {
+    dtRect = ScaleToOutsidePixelsOffset(paintBounds, scale.width, scale.height,
+                                        appUnitsPerDevPixel, residualOffset);
+
+    visibleRect = ScaleToOutsidePixelsOffset(
+                      aItem->GetBuildingRect(), scale.width, scale.height,
+                      appUnitsPerDevPixel, residualOffset)
+                      .Intersect(dtRect);
+  }
+
+  auto visibleSize = visibleRect.Size();
+  // these rectangles can overflow from scaling so try to
+  // catch that with IsEmpty() checks. See bug 1622126.
+  if (visibleSize.IsEmpty() || dtRect.IsEmpty()) {
+    return nullptr;
+  }
+
+  if (useBlobImage) {
+    // Display item bounds should be unscaled
+    aImageRect = visibleRect / layerScale;
+  } else {
+    // Display item bounds should be unscaled
+    aImageRect = dtRect / layerScale;
+  }
+
+  // We always paint items at 0,0 so the visibleRect that we use inside the blob
+  // is needs to be adjusted by the display item bounds top left.
+  visibleRect -= dtRect.TopLeft();
+
+  nsDisplayItemGeometry* geometry = fallbackData->mGeometry.get();
+
+  bool needPaint = true;
+
+  // nsDisplayFilters is rendered via BasicLayerManager which means the
+  // invalidate region is unknown until we traverse the displaylist contained by
+  // it.
+  if (geometry && !fallbackData->IsInvalid() &&
+      aItem->GetType() != DisplayItemType::TYPE_FILTER &&
+      aItem->GetType() != DisplayItemType::TYPE_SVG_WRAPPER && differentScale) {
+    nsRect invalid;
+    nsRegion invalidRegion;
+
+    if (aItem->IsInvalid(invalid)) {
+      invalidRegion.OrWith(paintBounds);
+    } else {
+      nsPoint shift = itemBounds.TopLeft() - geometry->mBounds.TopLeft();
+      geometry->MoveBy(shift);
+      aItem->ComputeInvalidationRegion(aDisplayListBuilder, geometry,
+                                       &invalidRegion);
+
+      nsRect lastBounds = fallbackData->mBounds;
+      lastBounds.MoveBy(shift);
+
+      if (!lastBounds.IsEqualInterior(paintBounds)) {
+        invalidRegion.OrWith(lastBounds);
+        invalidRegion.OrWith(paintBounds);
+      }
+    }
+    needPaint = !invalidRegion.IsEmpty();
+  }
+
+  if (needPaint || !fallbackData->GetImageKey()) {
+    fallbackData->mGeometry =
+        WrapUnique(aItem->AllocateGeometry(aDisplayListBuilder));
+
+    gfx::SurfaceFormat format = aItem->GetType() == DisplayItemType::TYPE_MASK
+                                    ? gfx::SurfaceFormat::A8
+                                    : (opacity == wr::OpacityType::Opaque
+                                           ? gfx::SurfaceFormat::B8G8R8X8
+                                           : gfx::SurfaceFormat::B8G8R8A8);
+    if (useBlobImage) {
+      MOZ_ASSERT(!opaqueRegion.IsComplex());
+
+      std::vector<RefPtr<ScaledFont>> fonts;
+      bool validFonts = true;
+      RefPtr<WebRenderDrawEventRecorder> recorder =
+          MakeAndAddRef<WebRenderDrawEventRecorder>(
+              [&](MemStream& aStream,
+                  std::vector<RefPtr<ScaledFont>>& aScaledFonts) {
+                size_t count = aScaledFonts.size();
+                aStream.write((const char*)&count, sizeof(count));
+                for (auto& scaled : aScaledFonts) {
+                  Maybe<wr::FontInstanceKey> key =
+                      mManager->WrBridge()->GetFontKeyForScaledFont(
+                          scaled, &aResources);
+                  if (key.isNothing()) {
+                    validFonts = false;
+                    break;
+                  }
+                  BlobFont font = {key.value(), scaled};
+                  aStream.write((const char*)&font, sizeof(font));
+                }
+                fonts = std::move(aScaledFonts);
+              });
+      RefPtr<gfx::DrawTarget> dummyDt = gfx::Factory::CreateDrawTarget(
+          gfx::BackendType::SKIA, gfx::IntSize(1, 1), format);
+      RefPtr<gfx::DrawTarget> dt = gfx::Factory::CreateRecordingDrawTarget(
+          recorder, dummyDt, (dtRect - dtRect.TopLeft()).ToUnknownRect());
+      if (!fallbackData->mBasicLayerManager) {
+        fallbackData->mBasicLayerManager =
+            new BasicLayerManager(BasicLayerManager::BLM_INACTIVE);
+      }
+      bool isInvalidated = PaintItemByDrawTarget(
+          aItem, dt, (dtRect / layerScale).TopLeft(),
+          /*aVisibleRect: */ dt->GetRect(), aDisplayListBuilder,
+          fallbackData->mBasicLayerManager, scale, highlight);
+      if (!isInvalidated) {
+        if (!aItem->GetBuildingRect().IsEqualInterior(
+                fallbackData->mBuildingRect)) {
+          // The building rect has changed but we didn't see any invalidations.
+          // We should still consider this an invalidation.
+          isInvalidated = true;
+        }
+      }
+
+      // the item bounds are relative to the blob origin which is
+      // dtRect.TopLeft()
+      recorder->FlushItem((dtRect - dtRect.TopLeft()).ToUnknownRect());
+      recorder->Finish();
+
+      if (!validFonts) {
+        gfxCriticalNote << "Failed serializing fonts for blob image";
+        return nullptr;
+      }
+
+      if (isInvalidated) {
+        Range<uint8_t> bytes((uint8_t*)recorder->mOutputStream.mData,
+                             recorder->mOutputStream.mLength);
+        wr::BlobImageKey key =
+            wr::BlobImageKey{mManager->WrBridge()->GetNextImageKey()};
+        wr::ImageDescriptor descriptor(visibleSize.ToUnknownSize(), 0,
+                                       dt->GetFormat(), opacity);
+        if (!aResources.AddBlobImage(
+                key, descriptor, bytes,
+                ViewAs<ImagePixel>(visibleRect,
+                                   PixelCastJustification::LayerIsImage))) {
+          return nullptr;
+        }
+        TakeExternalSurfaces(recorder, fallbackData->mExternalSurfaces,
+                             mManager->GetRenderRootStateManager(), aResources);
+        fallbackData->SetBlobImageKey(key);
+        fallbackData->SetFonts(fonts);
+      } else {
+        // If there is no invalidation region and we don't have a image key,
+        // it means we don't need to push image for the item.
+        if (!fallbackData->GetBlobImageKey().isSome()) {
+          return nullptr;
+        }
+      }
+    } else {
+      WebRenderImageData* imageData = fallbackData->PaintIntoImage();
+
+      imageData->CreateImageClientIfNeeded();
+      RefPtr<ImageClient> imageClient = imageData->GetImageClient();
+      RefPtr<ImageContainer> imageContainer =
+          LayerManager::CreateImageContainer();
+      bool isInvalidated = false;
+
+      {
+        UpdateImageHelper helper(imageContainer, imageClient,
+                                 dtRect.Size().ToUnknownSize(), format);
+        {
+          RefPtr<gfx::DrawTarget> dt = helper.GetDrawTarget();
+          if (!dt) {
+            return nullptr;
+          }
+          if (!fallbackData->mBasicLayerManager) {
+            fallbackData->mBasicLayerManager =
+                new BasicLayerManager(mManager->GetWidget());
+          }
+          isInvalidated = PaintItemByDrawTarget(
+              aItem, dt,
+              /*aOffset: */ aImageRect.TopLeft(),
+              /*aVisibleRect: */ dt->GetRect(), aDisplayListBuilder,
+              fallbackData->mBasicLayerManager, scale, highlight);
+        }
+
+        if (isInvalidated) {
+          // Update image if there it's invalidated.
+          if (!helper.UpdateImage()) {
+            return nullptr;
+          }
+        } else {
+          // If there is no invalidation region and we don't have a image key,
+          // it means we don't need to push image for the item.
+          if (!imageData->GetImageKey().isSome()) {
+            return nullptr;
+          }
+        }
+      }
+
+      // Force update the key in fallback data since we repaint the image in
+      // this path. If not force update, fallbackData may reuse the original key
+      // because it doesn't know UpdateImageHelper already updated the image
+      // container.
+      if (isInvalidated &&
+          !imageData->UpdateImageKey(imageContainer, aResources, true)) {
+        return nullptr;
+      }
+    }
+
+    fallbackData->mScale = scale;
+    fallbackData->SetInvalid(false);
+  }
+
+  if (useBlobImage) {
+    aResources.SetBlobImageVisibleArea(
+        fallbackData->GetBlobImageKey().value(),
+        ViewAs<ImagePixel>(visibleRect, PixelCastJustification::LayerIsImage));
+  }
+
+  // Update current bounds to fallback data
+  fallbackData->mBounds = paintBounds;
+  fallbackData->mBuildingRect = aItem->GetBuildingRect();
+
+  MOZ_ASSERT(fallbackData->GetImageKey());
+
+  return fallbackData.forget();
+}
+
+class WebRenderMaskData : public WebRenderUserData {
+ public:
+  explicit WebRenderMaskData(RenderRootStateManager* aManager,
+                             nsDisplayItem* aItem)
+      : WebRenderUserData(aManager, aItem),
+        mMaskStyle(nsStyleImageLayers::LayerType::Mask),
+        mShouldHandleOpacity(false) {
+    MOZ_COUNT_CTOR(WebRenderMaskData);
+  }
+  virtual ~WebRenderMaskData() {
+    MOZ_COUNT_DTOR(WebRenderMaskData);
+    ClearImageKey();
+  }
+
+  void ClearImageKey() {
+    if (mBlobKey) {
+      mManager->AddBlobImageKeyForDiscard(mBlobKey.value());
+    }
+    mBlobKey.reset();
+  }
+
+  UserDataType GetType() override { return UserDataType::eMask; }
+  static UserDataType Type() { return UserDataType::eMask; }
+
+  Maybe<wr::BlobImageKey> mBlobKey;
+  std::vector<RefPtr<gfx::ScaledFont>> mFonts;
+  std::vector<RefPtr<gfx::SourceSurface>> mExternalSurfaces;
+  LayerIntRect mItemRect;
+  nsPoint mMaskOffset;
+  nsStyleImageLayers mMaskStyle;
+  gfx::Size mScale;
+  bool mShouldHandleOpacity;
+};
+
+Maybe<wr::ImageMask> WebRenderCommandBuilder::BuildWrMaskImage(
+    nsDisplayMasksAndClipPaths* aMaskItem, wr::DisplayListBuilder& aBuilder,
+    wr::IpcResourceUpdateQueue& aResources, const StackingContextHelper& aSc,
+    nsDisplayListBuilder* aDisplayListBuilder,
+    const LayoutDeviceRect& aBounds) {
+  RefPtr<WebRenderMaskData> maskData =
+      CreateOrRecycleWebRenderUserData<WebRenderMaskData>(aMaskItem);
+
+  if (!maskData) {
+    return Nothing();
+  }
+
+  bool snap;
+  nsRect bounds = aMaskItem->GetBounds(aDisplayListBuilder, &snap);
+
+  const int32_t appUnitsPerDevPixel =
+      aMaskItem->Frame()->PresContext()->AppUnitsPerDevPixel();
+
+  Size scale = aSc.GetInheritedScale();
+  Size oldScale = maskData->mScale;
+  // This scale determination should probably be done using
+  // ChooseScaleAndSetTransform but for now we just fake it.
+  // We tolerate slight changes in scale so that we don't, for example,
+  // rerasterize on MotionMark
+  bool sameScale = FuzzyEqual(scale.width, oldScale.width, 1e-6f) &&
+                   FuzzyEqual(scale.height, oldScale.height, 1e-6f);
+
+  LayerIntRect itemRect =
+      LayerIntRect::FromUnknownRect(bounds.ScaleToOutsidePixels(
+          scale.width, scale.height, appUnitsPerDevPixel));
+
+  if (itemRect.IsEmpty()) {
+    return Nothing();
+  }
+
+  LayoutDeviceToLayerScale2D layerScale(scale.width, scale.height);
+  LayoutDeviceRect imageRect = LayerRect(itemRect) / layerScale;
+
+  nsPoint maskOffset = aMaskItem->ToReferenceFrame() - bounds.TopLeft();
+
+  nsRect dirtyRect;
+  // If this mask item is being painted for the first time, some members of
+  // WebRenderMaskData are still default initialized. This is intentional.
+  if (aMaskItem->IsInvalid(dirtyRect) ||
+      !itemRect.IsEqualInterior(maskData->mItemRect) ||
+      !(aMaskItem->Frame()->StyleSVGReset()->mMask == maskData->mMaskStyle) ||
+      maskOffset != maskData->mMaskOffset || !sameScale ||
+      aMaskItem->ShouldHandleOpacity() != maskData->mShouldHandleOpacity) {
+    IntSize size = itemRect.Size().ToUnknownSize();
+
+    std::vector<RefPtr<ScaledFont>> fonts;
+    bool validFonts = true;
+    RefPtr<WebRenderDrawEventRecorder> recorder =
+        MakeAndAddRef<WebRenderDrawEventRecorder>(
+            [&](MemStream& aStream,
+                std::vector<RefPtr<ScaledFont>>& aScaledFonts) {
+              size_t count = aScaledFonts.size();
+              aStream.write((const char*)&count, sizeof(count));
+
+              for (auto& scaled : aScaledFonts) {
+                Maybe<wr::FontInstanceKey> key =
+                    mManager->WrBridge()->GetFontKeyForScaledFont(scaled,
+                                                                  &aResources);
+                if (key.isNothing()) {
+                  validFonts = false;
+                  break;
+                }
+                BlobFont font = {key.value(), scaled};
+                aStream.write((const char*)&font, sizeof(font));
+              }
+
+              fonts = std::move(aScaledFonts);
+            });
+
+    RefPtr<DrawTarget> dummyDt = Factory::CreateDrawTarget(
+        BackendType::SKIA, IntSize(1, 1), SurfaceFormat::A8);
+    RefPtr<DrawTarget> dt = Factory::CreateRecordingDrawTarget(
+        recorder, dummyDt, IntRect(IntPoint(0, 0), size));
+
+    RefPtr<gfxContext> context = gfxContext::CreateOrNull(dt);
+    MOZ_ASSERT(context);
+
+    context->SetMatrix(context->CurrentMatrix()
+                           .PreTranslate(-itemRect.x, -itemRect.y)
+                           .PreScale(scale.width, scale.height));
+
+    bool maskPainted = false;
+    bool maskIsComplete =
+        aMaskItem->PaintMask(aDisplayListBuilder, context, &maskPainted);
+    if (!maskPainted) {
+      return Nothing();
+    }
+
+    // If a mask is incomplete or missing (e.g. it's display: none) the proper
+    // behaviour depends on the masked frame being html or svg.
+    //
+    // For an HTML frame:
+    //   According to css-masking spec, always create a mask surface when
+    //   we have any item in maskFrame even if all of those items are
+    //   non-resolvable <mask-sources> or <images> so continue with the
+    //   painting code. Note that in a common case of no layer of the mask being
+    //   complete or even partially complete then the mask surface will be
+    //   transparent black so this results in hiding the frame.
+    // For an SVG frame:
+    //   SVG 1.1 say that if we fail to resolve a mask, we should draw the
+    //   object unmasked so return Nothing().
+    if (!maskIsComplete &&
+        (aMaskItem->Frame()->GetStateBits() & NS_FRAME_SVG_LAYOUT)) {
+      return Nothing();
+    }
+
+    recorder->FlushItem(IntRect(0, 0, size.width, size.height));
+    recorder->Finish();
+
+    if (!validFonts) {
+      gfxCriticalNote << "Failed serializing fonts for blob mask image";
+      return Nothing();
+    }
+
+    Range<uint8_t> bytes((uint8_t*)recorder->mOutputStream.mData,
+                         recorder->mOutputStream.mLength);
+    wr::BlobImageKey key =
+        wr::BlobImageKey{mManager->WrBridge()->GetNextImageKey()};
+    wr::ImageDescriptor descriptor(size, 0, dt->GetFormat(),
+                                   wr::OpacityType::HasAlphaChannel);
+    if (!aResources.AddBlobImage(key, descriptor, bytes,
+                                 ImageIntRect(0, 0, size.width, size.height))) {
+      return Nothing();
+    }
+    maskData->ClearImageKey();
+    maskData->mBlobKey = Some(key);
+    maskData->mFonts = fonts;
+    TakeExternalSurfaces(recorder, maskData->mExternalSurfaces,
+                         mManager->GetRenderRootStateManager(), aResources);
+    if (maskIsComplete) {
+      maskData->mItemRect = itemRect;
+      maskData->mMaskOffset = maskOffset;
+      maskData->mScale = scale;
+      maskData->mMaskStyle = aMaskItem->Frame()->StyleSVGReset()->mMask;
+      maskData->mShouldHandleOpacity = aMaskItem->ShouldHandleOpacity();
+    }
+  }
+
+  wr::ImageMask imageMask;
+  imageMask.image = wr::AsImageKey(maskData->mBlobKey.value());
+  imageMask.rect = wr::ToLayoutRect(imageRect);
+  imageMask.repeat = false;
+  return Some(imageMask);
+}
+
+bool WebRenderCommandBuilder::PushItemAsImage(
+    nsDisplayItem* aItem, wr::DisplayListBuilder& aBuilder,
+    wr::IpcResourceUpdateQueue& aResources, const StackingContextHelper& aSc,
+    nsDisplayListBuilder* aDisplayListBuilder) {
+  LayoutDeviceRect imageRect;
+  RefPtr<WebRenderFallbackData> fallbackData = GenerateFallbackData(
+      aItem, aBuilder, aResources, aSc, aDisplayListBuilder, imageRect);
+  if (!fallbackData) {
+    return false;
+  }
+
+  wr::LayoutRect dest = wr::ToLayoutRect(imageRect);
+  gfx::SamplingFilter sampleFilter =
+      nsLayoutUtils::GetSamplingFilterForFrame(aItem->Frame());
+  aBuilder.PushImage(dest, dest, !aItem->BackfaceIsHidden(),
+                     wr::ToImageRendering(sampleFilter),
+                     fallbackData->GetImageKey().value());
+  return true;
+}
+
+void WebRenderCommandBuilder::RemoveUnusedAndResetWebRenderUserData() {
+  for (auto iter = mWebRenderUserDatas.Iter(); !iter.Done(); iter.Next()) {
+    WebRenderUserData* data = iter.Get()->GetKey();
+    if (!data->IsUsed()) {
+      nsIFrame* frame = data->GetFrame();
+
+      MOZ_ASSERT(frame->HasProperty(WebRenderUserDataProperty::Key()));
+
+      WebRenderUserDataTable* userDataTable =
+          frame->GetProperty(WebRenderUserDataProperty::Key());
+
+      MOZ_ASSERT(userDataTable->Count());
+
+      userDataTable->Remove(
+          WebRenderUserDataKey(data->GetDisplayItemKey(), data->GetType()));
+
+      if (!userDataTable->Count()) {
+        frame->RemoveProperty(WebRenderUserDataProperty::Key());
+        userDataTable = nullptr;
+      }
+
+      switch (data->GetType()) {
+        case WebRenderUserData::UserDataType::eCanvas:
+          mLastCanvasDatas.RemoveEntry(data->AsCanvasData());
+          break;
+        case WebRenderUserData::UserDataType::eLocalCanvas:
+          mLastLocalCanvasDatas.RemoveEntry(data->AsLocalCanvasData());
+          break;
+        case WebRenderUserData::UserDataType::eAnimation:
+          EffectCompositor::ClearIsRunningOnCompositor(
+              frame, GetDisplayItemTypeFromKey(data->GetDisplayItemKey()));
+          break;
+        default:
+          break;
+      }
+
+      iter.Remove();
+      continue;
+    }
+
+    data->SetUsed(false);
+  }
+}
+
+void WebRenderCommandBuilder::ClearCachedResources() {
+  RemoveUnusedAndResetWebRenderUserData();
+  // UserDatas should only be in the used state during a call to
+  // WebRenderCommandBuilder::BuildWebRenderCommands The should always be false
+  // upon return from BuildWebRenderCommands().
+  MOZ_RELEASE_ASSERT(mWebRenderUserDatas.Count() == 0);
+}
+
+WebRenderGroupData::WebRenderGroupData(
+    RenderRootStateManager* aRenderRootStateManager, nsDisplayItem* aItem)
+    : WebRenderUserData(aRenderRootStateManager, aItem) {
+  MOZ_COUNT_CTOR(WebRenderGroupData);
+}
+
+WebRenderGroupData::~WebRenderGroupData() {
+  MOZ_COUNT_DTOR(WebRenderGroupData);
+  GP("Group data destruct\n");
+  mSubGroup.ClearImageKey(mManager, true);
+  mFollowingGroup.ClearImageKey(mManager, true);
+}
+
+}  // namespace layers
+}  // namespace mozilla