Implement merging non-composited paint property nodes in the PACompositor.

third_party/WebKit/Source/platform/graphics/compositing/PaintArtifactCompositor.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "platform/graphics/compositing/PaintArtifactCompositor.h"
 
 #include "cc/layers/content_layer_client.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/picture_layer.h"
+#include "cc/playback/compositing_display_item.h"
 #include "cc/playback/display_item_list.h"
 #include "cc/playback/display_item_list_settings.h"
 #include "cc/playback/drawing_display_item.h"
+#include "cc/playback/filter_display_item.h"
+#include "cc/playback/float_clip_display_item.h"
 #include "cc/playback/transform_display_item.h"
 #include "cc/trees/clip_node.h"
 #include "cc/trees/effect_node.h"
 #include "cc/trees/layer_tree_host.h"
 #include "cc/trees/property_tree.h"
 #include "cc/trees/scroll_node.h"
 #include "cc/trees/transform_node.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "platform/graphics/paint/DrawingDisplayItem.h"
 #include "platform/graphics/paint/ForeignLayerDisplayItem.h"
+#include "platform/graphics/paint/GeometryMapper.h"
 #include "platform/graphics/paint/PaintArtifact.h"
+#include "platform/graphics/paint/PropertyTreeState.h"
 #include "platform/graphics/paint/RasterInvalidationTracking.h"
 #include "platform/graphics/paint/ScrollPaintPropertyNode.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebCompositorSupport.h"
 #include "public/platform/WebLayer.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/point_f.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/rect_f.h"
@@ skipping 193 matching lines @@
     // gfx::Rect bounds = gfx::SkIRectToRect(picture->cullRect().roundOut());
     // or use the visual rect directly. However, clip content layers attempt
     // to raster in a different space than that of the visual rects. We'll be
     // reworking visual rects further for SPv2, so for now we just pass a
     // visual rect large enough to make sure items raster.
     list->CreateAndAppendDrawingItem<cc::DrawingDisplayItem>(
         largeRect, sk_ref_sp(picture));
   }
 }
 
-static scoped_refptr<cc::DisplayItemList> recordPaintChunk(
-    const PaintArtifact& artifact,
-    const PaintChunk& chunk,
-    const gfx::Rect& combinedBounds) {
-  cc::DisplayItemListSettings settings;
-  scoped_refptr<cc::DisplayItemList> list =
-      cc::DisplayItemList::Create(settings);
-
-  gfx::Transform translation;
-  translation.Translate(-combinedBounds.x(), -combinedBounds.y());
-  // Passing combinedBounds as the visual rect for the begin/end transform item
-  // would normally be the sensible thing to do, but see comment above re:
-  // visual rects for drawing items and further rework in flight.
-  list->CreateAndAppendPairedBeginItem<cc::TransformDisplayItem>(translation);
-
-  const DisplayItemList& displayItems = artifact.getDisplayItemList();
-  for (const auto& displayItem : displayItems.itemsInPaintChunk(chunk))
-    appendDisplayItemToCcDisplayItemList(displayItem, list.get());
-
-  list->CreateAndAppendPairedEndItem<cc::EndTransformDisplayItem>();
-
-  list->Finalize();
-  return list;
-}
-
 scoped_refptr<cc::Layer> foreignLayerForPaintChunk(
     const PaintArtifact& paintArtifact,
     const PaintChunk& paintChunk,
     gfx::Vector2dF& layerOffset) {
   if (paintChunk.size() != 1)
     return nullptr;
 
   const auto& displayItem =
       paintArtifact.getDisplayItemList()[paintChunk.beginIndex];
   if (!displayItem.isForeignLayer())
     return nullptr;
 
   const auto& foreignLayerDisplayItem =
       static_cast<const ForeignLayerDisplayItem&>(displayItem);
   layerOffset = gfx::Vector2dF(foreignLayerDisplayItem.location().x(),
                                foreignLayerDisplayItem.location().y());
   scoped_refptr<cc::Layer> layer = foreignLayerDisplayItem.layer();
   layer->SetBounds(foreignLayerDisplayItem.bounds());
   layer->SetIsDrawable(true);
   return layer;
 }
 
 constexpr int kInvalidNodeId = -1;
 // cc's property trees use 0 for the root node (always non-null).
 constexpr int kRealRootNodeId = 0;
 // cc allocates special nodes for root effects such as the device scale.
 constexpr int kSecondaryRootNodeId = 1;
 constexpr int kPropertyTreeSequenceNumber = 1;
 
+enum EndDisplayItemType { EndTransform, EndClip, EndEffect };
+
+// Applies the clips between |localState| and |ancestorState| into a single
+// combined cc::FloatClipDisplayItem on |ccList|.
+static void applyClipsBetweenStates(const PropertyTreeState& localState,
+                       const PropertyTreeState& ancestorState,
+                       cc::DisplayItemList& ccList,
+                       Vector<EndDisplayItemType>& endDisplayItems,
+                       GeometryMapper& geometryMapper) {
+  DCHECK(localState.transform() == ancestorState.transform());
+#ifdef DCHECK_IS_ON
+  const TransformPaintPropertyNode* transformNode =
+      localState.clip()->localTransformSpace();
+  if (transformNode != ancestorState.transform()) {
+      bool success = false;
+      const TransformationMatrix& localToAncestorMatrix =
+          geometryMapper.localToAncestorMatrix(transformNode, ancestorState,
+                                               success);
+      DCHECK(success);
+      // Clips are only in descendant spaces that are transformed by one
+      // or more scrolls.
+      DCHECK(localToAncestorMatrix.isIdentityOrTranslation());
+  }
+#endif
+
+  static FloatRect infinteFloatRect = FloatRect(LayoutRect::infiniteIntRect());
+  FloatRect combinedClip;
+  bool success = false;
+  combinedClip = geometryMapper.localToVisualRectInAncestorSpace(
+      infinteFloatRect, localState, ancestorState, success);
+  DCHECK(success);
+  if (combinedClip == infinteFloatRect)
+    return;
+
+  ccList.CreateAndAppendPairedBeginItem<cc::FloatClipDisplayItem>(
+      gfx::RectF(combinedClip));
+  endDisplayItems.push_back(EndClip);
+}
+
+static void recordPairedBeginDisplayItems(
+    const Vector<PropertyTreeState>& pairedStates,
+    const PropertyTreeState& pendingLayerState,
+    cc::DisplayItemList& ccList,
+    Vector<EndDisplayItemType>& endDisplayItems,
+    GeometryMapper& geometryMapper) {
+  PropertyTreeState mappedClipDestinationSpace = pendingLayerState;
+  PropertyTreeState clipSpace = pendingLayerState;
+  bool hasClip = false;
+
+  for (Vector<PropertyTreeState>::const_reverse_iterator pairedState =
+           pairedStates.rbegin();
+       pairedState != pairedStates.rend(); ++pairedState) {
+    switch (pairedState->innermostNode()) {
+      case PropertyTreeState::Transform: {
+        if (hasClip) {
+          applyClipsBetweenStates(clipSpace, mappedClipDestinationSpace, ccList,
+                     endDisplayItems, geometryMapper);
+        }
+        mappedClipDestinationSpace = *pairedState;
+        clipSpace = *pairedState;
+
+        gfx::Transform transform(gfx::Transform::kSkipInitialization);
+        transform.matrix() = TransformationMatrix::toSkMatrix44(
+            pairedState->transform()->matrix());
+
+        ccList.CreateAndAppendPairedBeginItem<cc::TransformDisplayItem>(
+            transform);
+        endDisplayItems.push_back(EndTransform);
+        break;
+      }
+      case PropertyTreeState::Clip: {
+        // Clips are handled in |applyClips| when ending the iterator, or
+        // transitioning between transform spaces. Here we store off the
+        // PropertyTreeState of the first found clip, under the transform of
+        // pairedState->transform(). All subsequent clips before applying the
+        // transform will be applied in applyClips.
+        clipSpace = *pairedState;
+        hasClip = true;
+#ifdef DCHECK_IS_ON
+        if (pairedState->clip()->localTransformSpace() !=
+            pairedState->transform()) {
+          const TransformationMatrix& localTransformMatrix =
+              pairedState->effect()->localTransformSpace()->matrix();
+          // Clips are only in descendant spaces that are transformed by scroll.
+          DCHECK(localTransformMatrix.isIdentityOrTranslation());
+        }
+#endif
+        break;
+      }
+      case PropertyTreeState::Effect: {
+        // TODO(chrishtr): skip effect and/or compositing display items if
+        // not necessary.
+
+        FloatRect clipRect =
+            pairedState->effect()->outputClip()->clipRect().rect();
+        // TODO(chrishtr): specify origin of the filter.
+        FloatPoint filterOrigin;
+        if (pairedState->effect()->localTransformSpace() !=
+            pairedState->transform()) {
+          bool success = false;
+          const TransformPaintPropertyNode* transformNode =
+              pairedState->effect()->localTransformSpace();
+          const TransformationMatrix& localToAncestorMatrix =
+              geometryMapper.localToAncestorMatrix(transformNode, *pairedState,
+                                                   success);
+          DCHECK(success);
+          // Effects are only in descendant spaces that are transformed by one
+          // or more scrolls.
+          DCHECK(localToAncestorMatrix.isIdentityOrTranslation());
+
+          clipRect = localToAncestorMatrix.mapRect(clipRect);
+          filterOrigin = localToAncestorMatrix.mapPoint(filterOrigin);
+        }
+
+        ccList.CreateAndAppendPairedBeginItem<cc::FilterDisplayItem>(
+            pairedState->effect()->filter().asCcFilterOperations(),
+            pairedState->effect()->outputClip()->clipRect().rect(),
+            gfx::PointF(filterOrigin.x(), filterOrigin.y()));
+        const bool kLcdTextRequiresOpaqueLayer = true;
+        ccList.CreateAndAppendPairedBeginItem<cc::CompositingDisplayItem>(
+            static_cast<uint8_t>(
+                gfx::ToFlooredInt(255 * pairedState->effect()->opacity())),
+            pairedState->effect()->blendMode(),
+            // TODO(chrishtr): compute bounds as necessary.
+            nullptr, nullptr, kLcdTextRequiresOpaqueLayer);
+        endDisplayItems.push_back(EndEffect);
+        break;
+      }
+      case PropertyTreeState::None:
+        break;
+    }
+  }
+
+  if (hasClip) {
+    applyClipsBetweenStates(clipSpace, mappedClipDestinationSpace, ccList, endDisplayItems,
+               geometryMapper);
+  }
+}
+
+static void recordPairedEndDisplayItems(
+    const Vector<EndDisplayItemType>& endDisplayItemTypes,
+    cc::DisplayItemList* ccList) {
+  for (Vector<EndDisplayItemType>::const_reverse_iterator endType =
+           endDisplayItemTypes.rbegin();
+       endType != endDisplayItemTypes.rend(); ++endType) {
+    switch (*endType) {
+      case EndTransform:
+        ccList->CreateAndAppendPairedEndItem<cc::EndTransformDisplayItem>();
+        break;
+      case EndClip:
+        ccList->CreateAndAppendPairedEndItem<cc::EndFloatClipDisplayItem>();
+        break;
+      case EndEffect:
+        ccList->CreateAndAppendPairedEndItem<cc::EndCompositingDisplayItem>();
+        ccList->CreateAndAppendPairedEndItem<cc::EndFilterDisplayItem>();
+        break;
+    }
+  }
+}
+
 }  // namespace
 
+scoped_refptr<cc::DisplayItemList> PaintArtifactCompositor::recordPendingLayer(
+    const PaintArtifact& artifact,
+    const PendingLayer& pendingLayer,
+    const gfx::Rect& combinedBounds,
+    GeometryMapper& geometryMapper) {
+  cc::DisplayItemListSettings settings;
+  scoped_refptr<cc::DisplayItemList> ccList =
+      cc::DisplayItemList::Create(settings);
+
+  gfx::Transform translation;
+  translation.Translate(-combinedBounds.x(), -combinedBounds.y());
+  // Passing combinedBounds as the visual rect for the begin/end transform item
+  // would normally be the sensible thing to do, but see comment above re:
+  // visual rects for drawing items and further rework in flight.
+  ccList->CreateAndAppendPairedBeginItem<cc::TransformDisplayItem>(translation);
+
+  const DisplayItemList& displayItems = artifact.getDisplayItemList();
+  for (const auto& paintChunk : pendingLayer.paintChunks) {
+    const PropertyTreeState* state = &paintChunk->properties.propertyTreeState;
+    PropertyTreeStateIterator iterator(*state);
+    Vector<PropertyTreeState> pairedStates;
+    for (; state && *state != pendingLayer.propertyTreeState;
+         state = iterator.next()) {
+      if (state->innermostNode() != PropertyTreeState::None)
+        pairedStates.push_back(*state);
+    }
+
+    // TODO(chrishtr): we can avoid some extra paired display items if
+    // multiple PaintChunks share them. We can also collapse clips between
+    // transforms into single clips in the same way that PaintLayerClipper does.

[trchen, 2016/12/22 22:21:24]

Sharing is required for effect node, otherwise grouping won't work correctly.

For transform and clip I feel more like just emit a drawing display item that
does
{ canvas->setMatrix(combinedTransform); canvas->clipRegion(combinedClip,
SkClipOp::kReplace); }
Less hassle than sharing & collapsing the pairs. I don't feel strongly about
either way though.

[chrishtr, 2016/12/22 22:28:45]

Sure, but it's not always possible.
That would be ideal, but it's not easy to do performantly.

+    Vector<EndDisplayItemType> endDisplayItems;
+
+    recordPairedBeginDisplayItems(pairedStates, pendingLayer.propertyTreeState,
+                                  *ccList.get(), endDisplayItems,
+                                  geometryMapper);
+
+    for (const auto& displayItem : displayItems.itemsInPaintChunk(*paintChunk))
+      appendDisplayItemToCcDisplayItemList(displayItem, ccList.get());
+
+    recordPairedEndDisplayItems(endDisplayItems, ccList.get());
+  }
+
+  ccList->CreateAndAppendPairedEndItem<cc::EndTransformDisplayItem>();
+
+  ccList->Finalize();
+  return ccList;
+}
+
 std::unique_ptr<PaintArtifactCompositor::ContentLayerClientImpl>
 PaintArtifactCompositor::clientForPaintChunk(
     const PaintChunk& paintChunk,
     const PaintArtifact& paintArtifact) {
   // TODO(chrishtr): for now, just using a linear walk. In the future we can
   // optimize this by using the same techniques used in PaintController for
   // display lists.
   for (auto& client : m_contentLayerClients) {
     if (client && client->matches(paintChunk))
       return std::move(client);
   }
 
   return WTF::wrapUnique(new ContentLayerClientImpl(
       paintChunk.id
           ? *paintChunk.id
           : paintArtifact.getDisplayItemList()[paintChunk.beginIndex].getId()));
 }
 
-scoped_refptr<cc::Layer> PaintArtifactCompositor::layerForPaintChunk(
+scoped_refptr<cc::Layer>
+PaintArtifactCompositor::compositedLayerForPendingLayer(
     const PaintArtifact& paintArtifact,
-    const PaintChunk& paintChunk,
+    const PendingLayer& pendingLayer,
     gfx::Vector2dF& layerOffset,
     Vector<std::unique_ptr<ContentLayerClientImpl>>& newContentLayerClients,
-    RasterInvalidationTracking* tracking,
-    bool storeDebugInfo) {
-  DCHECK(paintChunk.size());
+    RasterInvalidationTrackingMap<const PaintChunk>* trackingMap,
+    bool storeDebugInfo,
+    GeometryMapper& geometryMapper) {
+  DCHECK(pendingLayer.paintChunks.size());
+  const PaintChunk& firstPaintChunk = *pendingLayer.paintChunks[0];
+  DCHECK(firstPaintChunk.size());
+#if DCHECK_IS_ON
+  for (const auto& paintChunk : pendingLayer.paintChunks) {
+    DCHECK(paintChunk.properties == firstPaintChunk.properties);
+  }
+#endif
 
   // If the paint chunk is a foreign layer, just return that layer.
-  if (scoped_refptr<cc::Layer> foreignLayer =
-          foreignLayerForPaintChunk(paintArtifact, paintChunk, layerOffset))
+  if (scoped_refptr<cc::Layer> foreignLayer = foreignLayerForPaintChunk(
+          paintArtifact, firstPaintChunk, layerOffset)) {
+    DCHECK(pendingLayer.paintChunks.size() == 1);
     return foreignLayer;
+  }
 
   // The common case: create or reuse a PictureLayer for painted content.
   std::unique_ptr<ContentLayerClientImpl> contentLayerClient =
-      clientForPaintChunk(paintChunk, paintArtifact);
+      clientForPaintChunk(firstPaintChunk, paintArtifact);
 
-  gfx::Rect combinedBounds = enclosingIntRect(paintChunk.bounds);
-  scoped_refptr<cc::DisplayItemList> displayList =
-      recordPaintChunk(paintArtifact, paintChunk, combinedBounds);
+  gfx::Rect ccCombinedBounds(enclosingIntRect(pendingLayer.bounds));

[trchen, 2016/12/22 22:21:24]

In PendingLayer::add it seemed to me pendingLayer.bounds is in screen
coordinate? Did we convert it to local rect somewhere?

[chrishtr, 2016/12/22 22:28:45]

It's in the space of the transform node of the first paint chunk. I see there is
a bug in that I'm not mapping subsequent chunks
in the same PaintLayer to that space, will fix.

+
+  scoped_refptr<cc::DisplayItemList> displayList = recordPendingLayer(
+      paintArtifact, pendingLayer, ccCombinedBounds, geometryMapper);
   contentLayerClient->SetDisplayList(std::move(displayList));
-  contentLayerClient->SetPaintableRegion(gfx::Rect(combinedBounds.size()));
+  contentLayerClient->SetPaintableRegion(gfx::Rect(ccCombinedBounds.size()));
 
-  layerOffset = combinedBounds.OffsetFromOrigin();
+  layerOffset = ccCombinedBounds.OffsetFromOrigin();
+
   scoped_refptr<cc::PictureLayer> ccPictureLayer =
       contentLayerClient->ccPictureLayer();
-  ccPictureLayer->SetBounds(combinedBounds.size());
+  ccPictureLayer->SetBounds(ccCombinedBounds.size());
   ccPictureLayer->SetIsDrawable(true);
-  if (paintChunk.knownToBeOpaque)
-    ccPictureLayer->SetContentsOpaque(true);
-  DCHECK(!tracking ||
-         tracking->trackedRasterInvalidations.size() ==
-             paintChunk.rasterInvalidationRects.size());
+  ccPictureLayer->SetContentsOpaque(pendingLayer.knownToBeOpaque);
+  contentLayerClient->clearPaintChunkDebugData();
 
-  contentLayerClient->clearPaintChunkDebugData();
-  if (storeDebugInfo) {
-    contentLayerClient->addPaintChunkDebugData(
-        paintArtifact.getDisplayItemList().subsequenceAsJSON(
-            paintChunk.beginIndex, paintChunk.endIndex,
-            DisplayItemList::SkipNonDrawings |
-                DisplayItemList::ShownOnlyDisplayItemTypes));
-  }
+  for (const auto& paintChunk : pendingLayer.paintChunks) {
+    RasterInvalidationTracking* rasterTracking =
+        trackingMap ? trackingMap->find(paintChunk) : nullptr;
+    DCHECK(!rasterTracking ||
+           rasterTracking->trackedRasterInvalidations.size() ==
+               paintChunk->rasterInvalidationRects.size());
 
-  for (unsigned index = 0; index < paintChunk.rasterInvalidationRects.size();
-       ++index) {
-    IntRect rect(enclosingIntRect(paintChunk.rasterInvalidationRects[index]));
-    gfx::Rect ccInvalidationRect(rect.x(), rect.y(), std::max(0, rect.width()),
-                                 std::max(0, rect.height()));
-    // Raster paintChunk.rasterInvalidationRects is in the space of the
-    // containing transform node, so need to subtract off the layer offset.
-    ccInvalidationRect.Offset(-combinedBounds.OffsetFromOrigin());
-    contentLayerClient->setNeedsDisplayRect(
-        ccInvalidationRect,
-        tracking ? &tracking->trackedRasterInvalidations[index] : nullptr);
+    if (storeDebugInfo) {
+      contentLayerClient->addPaintChunkDebugData(
+          paintArtifact.getDisplayItemList().subsequenceAsJSON(
+              paintChunk->beginIndex, paintChunk->endIndex,
+              DisplayItemList::SkipNonDrawings |
+                  DisplayItemList::ShownOnlyDisplayItemTypes));
+    }
+
+    for (unsigned index = 0; index < paintChunk->rasterInvalidationRects.size();
+         ++index) {
+      IntRect rect(
+          enclosingIntRect(paintChunk->rasterInvalidationRects[index]));
+      gfx::Rect ccInvalidationRect(rect.x(), rect.y(),
+                                   std::max(0, rect.width()),
+                                   std::max(0, rect.height()));
+      if (ccInvalidationRect.IsEmpty())
+        continue;
+      // Raster paintChunk.rasterInvalidationRects is in the space of the
+      // containing transform node, so need to subtract off the layer offset.
+      ccInvalidationRect.Offset(-ccCombinedBounds.OffsetFromOrigin());
+      contentLayerClient->setNeedsDisplayRect(
+          ccInvalidationRect,
+          rasterTracking ? &rasterTracking->trackedRasterInvalidations[index]
+                         : nullptr);
+    }
   }
 
   newContentLayerClients.append(std::move(contentLayerClient));
   return ccPictureLayer;
 }
 
 namespace {
 
 class PropertyTreeManager {
   WTF_MAKE_NONCOPYABLE(PropertyTreeManager);
@@ skipping 292 matching lines @@
   scrollTree().set_needs_update(true);
 }
 
 unsigned depth(const EffectPaintPropertyNode* node) {
   unsigned result = 0;
   for (; node; node = node->parent())
     result++;
   return result;
 }
 
+// TODO(chrishtr): templatize this to avoid duplication of
+// GeometryMapper::leastCommonAncestor.
 const EffectPaintPropertyNode* lowestCommonAncestor(
     const EffectPaintPropertyNode* nodeA,
     const EffectPaintPropertyNode* nodeB) {
   // Optimized common case.
   if (nodeA == nodeB)
     return nodeA;
 
   unsigned depthA = depth(nodeA), depthB = depth(nodeB);
   while (depthA > depthB) {
     nodeA = nodeA->parent();
@@ skipping 94 matching lines @@
 
   dummyLayer->set_property_tree_sequence_number(kPropertyTreeSequenceNumber);
   dummyLayer->SetTransformTreeIndex(kSecondaryRootNodeId);
   dummyLayer->SetClipTreeIndex(outputClipId);
   dummyLayer->SetEffectTreeIndex(effectNode.id);
   dummyLayer->SetScrollTreeIndex(kRealRootNodeId);
 }
 
 }  // namespace
 
+bool PaintArtifactCompositor::canMergeInto(
+    const PaintChunk& newChunk,
+    const PendingLayer& candidatePendingLayer) {
+  DCHECK(candidatePendingLayer.paintChunks.size() >= 1);
+  PropertyTreeStateIterator iterator(newChunk.properties.propertyTreeState);
+  for (const PropertyTreeState* currentState =
+           &newChunk.properties.propertyTreeState;
+       currentState; currentState = iterator.next()) {
+    if (currentState->hasDirectCompositingReasons())
+      return false;
+    if (*currentState == candidatePendingLayer.propertyTreeState)
+      return true;
+  }
+  return false;
+}
+
+bool PaintArtifactCompositor::overlaps(

[trchen, 2016/12/22 22:21:24]

nits: I think it should be named "possiblyOverlap" with a comment saying that
false positive may be returned but no false negative.

[chrishtr, 2016/12/22 22:28:45]

Done.

+    const PaintChunk& paintChunk,
+    const PendingLayer& candidatePendingLayer,
+    GeometryMapper& geometryMapper) {
+  // TODO(chrishtr): implement
+  return true;
+}
+
+PaintArtifactCompositor::PendingLayer::PendingLayer(
+    const PaintChunk& firstPaintChunk)
+    : knownToBeOpaque(true),
+      backfaceHidden(firstPaintChunk.properties.backfaceHidden),
+      propertyTreeState(firstPaintChunk.properties.propertyTreeState) {
+  add(firstPaintChunk);
+}
+
+void PaintArtifactCompositor::PendingLayer::add(const PaintChunk& paintChunk) {
+  DCHECK(paintChunk.properties.backfaceHidden == backfaceHidden);
+  paintChunks.append(&paintChunk);
+  bounds.unite(paintChunk.bounds);
+  knownToBeOpaque = knownToBeOpaque && paintChunk.knownToBeOpaque;

[trchen, 2016/12/22 22:21:24]

This looks wrong. A layer is opaque as long as there is one chunk that's opaque
and covers the layer rect. Also even if every chunks are opaque, the layer is
not if the union'd region is not a rect.

[chrishtr, 2016/12/22 22:28:45]

Good point, will fix.

+}
+
+void PaintArtifactCompositor::collectPendingLayers(
+    const Vector<PaintChunk>& paintChunks,
+    Vector<PendingLayer>& pendingLayers,
+    GeometryMapper& geometryMapper) {
+  // n = # of paint chunks. Memoizing canMergeInto() can get it to O(n^2), and
+  // other heuristics can make worst-case behavior better.
+  for (const PaintChunk& paintChunk : paintChunks) {
+    bool createNew = true;
+    for (Vector<PendingLayer>::reverse_iterator candidatePendingLayer =
+             pendingLayers.rbegin();
+         candidatePendingLayer != pendingLayers.rend();
+         ++candidatePendingLayer) {
+      if (canMergeInto(paintChunk, *candidatePendingLayer)) {
+        candidatePendingLayer->add(paintChunk);
+        createNew = false;
+        break;
+      }
+      if (overlaps(paintChunk, *candidatePendingLayer, geometryMapper)) {
+        break;
+      }
+    }
+    if (createNew)
+      pendingLayers.append(PendingLayer(paintChunk));
+  }
+}
+
 void PaintArtifactCompositor::update(
     const PaintArtifact& paintArtifact,
     RasterInvalidationTrackingMap<const PaintChunk>* rasterChunkInvalidations,
     bool storeDebugInfo) {
   DCHECK(m_rootLayer);
 
   cc::LayerTree* layerTree = m_rootLayer->GetLayerTree();
 
   // The tree will be null after detaching and this update can be ignored.
   // See: WebViewImpl::detachPaintArtifactCompositor().
   if (!layerTree)
     return;
 
   if (m_extraDataForTestingEnabled)
     m_extraDataForTesting = WTF::wrapUnique(new ExtraDataForTesting);
 
   m_rootLayer->RemoveAllChildren();
   m_rootLayer->set_property_tree_sequence_number(kPropertyTreeSequenceNumber);
 
   PropertyTreeManager propertyTreeManager(*layerTree->property_trees(),
                                           m_rootLayer.get());
 
+  Vector<PendingLayer, 0> pendingLayers;
+  GeometryMapper geometryMapper;
+  collectPendingLayers(paintArtifact.paintChunks(), pendingLayers,
+                       geometryMapper);
+
   Vector<std::unique_ptr<ContentLayerClientImpl>> newContentLayerClients;
   newContentLayerClients.reserveCapacity(paintArtifact.paintChunks().size());
-  for (const PaintChunk& paintChunk : paintArtifact.paintChunks()) {
+  for (const PendingLayer& pendingLayer : pendingLayers) {
     gfx::Vector2dF layerOffset;
-    scoped_refptr<cc::Layer> layer = layerForPaintChunk(
-        paintArtifact, paintChunk, layerOffset, newContentLayerClients,
-        rasterChunkInvalidations ? rasterChunkInvalidations->find(&paintChunk)
-                                 : nullptr,
-        storeDebugInfo);
+    scoped_refptr<cc::Layer> layer = compositedLayerForPendingLayer(
+        paintArtifact, pendingLayer, layerOffset, newContentLayerClients,
+        rasterChunkInvalidations, storeDebugInfo, geometryMapper);
 
     int transformId = propertyTreeManager.compositorIdForTransformNode(
-        paintChunk.properties.propertyTreeState.transform());
+        pendingLayer.propertyTreeState.transform());
     int scrollId = propertyTreeManager.compositorIdForScrollNode(
-        paintChunk.properties.propertyTreeState.scroll());
+        pendingLayer.propertyTreeState.scroll());
     int clipId = propertyTreeManager.compositorIdForClipNode(
-        paintChunk.properties.propertyTreeState.clip());
+        pendingLayer.propertyTreeState.clip());
     int effectId = propertyTreeManager.switchToEffectNode(
-        *paintChunk.properties.propertyTreeState.effect());
+        *pendingLayer.propertyTreeState.effect());
 
     propertyTreeManager.updateScrollOffset(layer->id(), scrollId);
 
     layer->set_offset_to_transform_parent(layerOffset);
 
     m_rootLayer->AddChild(layer);
     layer->set_property_tree_sequence_number(kPropertyTreeSequenceNumber);
     layer->SetTransformTreeIndex(transformId);
     layer->SetClipTreeIndex(clipId);
     layer->SetEffectTreeIndex(effectId);
     layer->SetScrollTreeIndex(scrollId);
 
     // TODO(jbroman): This probably shouldn't be necessary, but it is still
     // queried by RenderSurfaceImpl.
     layer->Set3dSortingContextId(layerTree->property_trees()
                                      ->transform_tree.Node(transformId)
                                      ->sorting_context_id);
 
-    layer->SetShouldCheckBackfaceVisibility(
-        paintChunk.properties.backfaceHidden);
+    layer->SetShouldCheckBackfaceVisibility(pendingLayer.backfaceHidden);
 
     if (m_extraDataForTestingEnabled)
       m_extraDataForTesting->contentLayers.append(layer);
   }
   m_contentLayerClients.clear();
   m_contentLayerClients.swap(newContentLayerClients);
 
   // Mark the property trees as having been rebuilt.
   layerTree->property_trees()->sequence_number = kPropertyTreeSequenceNumber;
   layerTree->property_trees()->needs_rebuild = false;
   layerTree->property_trees()->ResetCachedData();
 }
 
 }  // namespace blink