Bug 1500864 - Cull items within opacity:0 containers when merging with retained display lists. r=mstange

Differential Revision: https://phabricator.services.mozilla.com/D14304

--HG--
extra : moz-landing-system : lando

layout/painting/RetainedDisplayListBuilder.cpp

@@ -13,6 +13,7 @@
 #include "nsSubDocumentFrame.h"
 #include "nsViewManager.h"
 #include "nsCanvasFrame.h"
+#include "mozilla/AutoRestore.h"
 
 /**
  * Code for doing display list building for a modified subset of the window,
@@ -317,8 +318,25 @@ class MergeState {
     MOZ_RELEASE_ASSERT(mOldItems.Length() == mOldDAG.Length());
   }
 
-  MergedListIndex ProcessItemFromNewList(
+  // Items within an opacity:0 container (excluding plugins and hit test info)
+  // aren't needed, so we can strip them out from both the old and new lists.
+  // Do this silently, so that these changes don't result in us reporting that
+  // the display list changed. Both FrameLayerBuilder and
+  // WebRenderCommandBuilder also do this removal, so it's functionally correct
+  // to report that the display list is identical.
+  bool ShouldSilentlyDiscardItem(nsDisplayItem* aItem) {
+    return aItem && mBuilder->mCurrentSubtreeIsForEventsAndPluginsOnly &&
+           (aItem->GetType() != DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO &&
+            aItem->GetType() != DisplayItemType::TYPE_PLUGIN);
+  }
+
+  Maybe<MergedListIndex> ProcessItemFromNewList(
       nsDisplayItem* aNewItem, const Maybe<MergedListIndex>& aPreviousItem) {
+    if (ShouldSilentlyDiscardItem(aNewItem)) {
+      aNewItem->Destroy(mBuilder->Builder());
+      return aPreviousItem;
+    }
+
     OldListIndex oldIndex;
     if (!HasModifiedFrame(aNewItem) &&
         HasMatchingItemInOldList(aNewItem, &oldIndex)) {
@@ -344,8 +362,7 @@ class MergeState {
           Maybe<const ActiveScrolledRoot*> containerASRForChildren;
           if (mBuilder->MergeDisplayLists(
                   aNewItem->GetChildren(), oldItem->GetChildren(),
-                  destItem->GetChildren(), containerASRForChildren,
-                  aNewItem->GetPerFrameKey())) {
+                  destItem->GetChildren(), containerASRForChildren, aNewItem)) {
             destItem->InvalidateCachedChildInfo();
             mResultIsModified = true;
           }
@@ -363,12 +380,12 @@ class MergeState {
         } else {
           aNewItem->Destroy(mBuilder->Builder());
         }
-        return newIndex;
+        return Some(newIndex);
       }
     }
     mResultIsModified = true;
-    return AddNewNode(aNewItem, Nothing(), Span<MergedListIndex>(),
-                      aPreviousItem);
+    return Some(AddNewNode(aNewItem, Nothing(), Span<MergedListIndex>(),
+                           aPreviousItem));
   }
 
   bool ShouldUseNewItem(nsDisplayItem* aNewItem) {
@@ -505,16 +522,20 @@ class MergeState {
   void ProcessOldNode(OldListIndex aNode,
                       nsTArray<MergedListIndex>&& aDirectPredecessors) {
     nsDisplayItem* item = mOldItems[aNode.val].mItem;
-    if (mOldItems[aNode.val].IsChanged() || HasModifiedFrame(item)) {
+    if (ShouldSilentlyDiscardItem(item)) {
+      // If the item should be discarded, then just silently drop it and
+      // don't mark the display list as being modified.
+      mOldItems[aNode.val].Discard(mBuilder, std::move(aDirectPredecessors));
+    } else if (mOldItems[aNode.val].IsChanged() || HasModifiedFrame(item)) {
       mOldItems[aNode.val].Discard(mBuilder, std::move(aDirectPredecessors));
       mResultIsModified = true;
     } else {
       if (item->GetChildren()) {
         Maybe<const ActiveScrolledRoot*> containerASRForChildren;
         nsDisplayList empty;
-        if (mBuilder->MergeDisplayLists(
-                &empty, item->GetChildren(), item->GetChildren(),
-                containerASRForChildren, item->GetPerFrameKey())) {
+        if (mBuilder->MergeDisplayLists(&empty, item->GetChildren(),
+                                        item->GetChildren(),
+                                        containerASRForChildren, item)) {
           item->InvalidateCachedChildInfo();
           mResultIsModified = true;
         }
@@ -630,13 +651,20 @@ bool RetainedDisplayListBuilder::MergeDisplayLists(
     nsDisplayList* aNewList, RetainedDisplayList* aOldList,
     RetainedDisplayList* aOutList,
     mozilla::Maybe<const mozilla::ActiveScrolledRoot*>& aOutContainerASR,
-    uint32_t aOuterKey) {
-  MergeState merge(this, *aOldList, aOuterKey);
+    nsDisplayItem* aOuterItem) {
+  MergeState merge(this, *aOldList,
+                   aOuterItem ? aOuterItem->GetPerFrameKey() : 0);
+
+  AutoRestore<bool> restoreForEventAndPluginsOnly(
+      mCurrentSubtreeIsForEventsAndPluginsOnly);
+  if (aOuterItem && aOuterItem->GetType() == DisplayItemType::TYPE_OPACITY &&
+      static_cast<nsDisplayOpacity*>(aOuterItem)->ForEventsAndPluginsOnly()) {
+    mCurrentSubtreeIsForEventsAndPluginsOnly = true;
+  }
 
   Maybe<MergedListIndex> previousItemIndex;
   while (nsDisplayItem* item = aNewList->RemoveBottom()) {
-    previousItemIndex =
-        Some(merge.ProcessItemFromNewList(item, previousItemIndex));
+    previousItemIndex = merge.ProcessItemFromNewList(item, previousItemIndex);
   }
 
   *aOutList = merge.Finalize();

layout/painting/RetainedDisplayListBuilder.h

@@ -95,7 +95,8 @@ RetainedDisplayListData* GetOrSetRetainedDisplayListData(nsIFrame* aRootFrame);
 struct RetainedDisplayListBuilder {
   RetainedDisplayListBuilder(nsIFrame* aReferenceFrame,
                              nsDisplayListBuilderMode aMode, bool aBuildCaret)
-      : mBuilder(aReferenceFrame, aMode, aBuildCaret, true) {}
+      : mBuilder(aReferenceFrame, aMode, aBuildCaret, true),
+        mCurrentSubtreeIsForEventsAndPluginsOnly(false) {}
   ~RetainedDisplayListBuilder() { mList.DeleteAll(&mBuilder); }
 
   nsDisplayListBuilder* Builder() { return &mBuilder; }
@@ -122,11 +123,20 @@ struct RetainedDisplayListBuilder {
                              AnimatedGeometryRoot* aAGR,
                              uint32_t aCallerKey = 0,
                              uint32_t aNestingDepth = 0);
+
+  /**
+   * Merges items from aNewList into non-invalidated items from aOldList and
+   * stores the result in aOutList.
+   *
+   * aOuterItem is a pointer to an item that owns one of the lists, if
+   * available. If both lists are populated, then both outer items must not be
+   * invalidated, and identical, so either can be passed here.
+   */
   bool MergeDisplayLists(
       nsDisplayList* aNewList, RetainedDisplayList* aOldList,
       RetainedDisplayList* aOutList,
       mozilla::Maybe<const mozilla::ActiveScrolledRoot*>& aOutContainerASR,
-      uint32_t aOuterKey = 0);
+      nsDisplayItem* aOuterItem = nullptr);
 
   bool ComputeRebuildRegion(nsTArray<nsIFrame*>& aModifiedFrames,
                             nsRect* aOutDirty,
@@ -145,6 +155,10 @@ struct RetainedDisplayListBuilder {
   nsDisplayListBuilder mBuilder;
   RetainedDisplayList mList;
   WeakFrame mPreviousCaret;
+
+  // True if we're currently within an opacity:0 container, and only
+  // plugin and hit test items should be considered.
+  bool mCurrentSubtreeIsForEventsAndPluginsOnly;
 };
 
 #endif  // RETAINEDDISPLAYLISTBUILDER_H_

layout/painting/crashtests/1514544-1.html

@@ -0,0 +1,15 @@
+<html class="reftest-wait">
+<script>
+setTimeout(function() {
+  a.appendChild(b);
+  document.documentElement.className = "";
+}, 100)
+</script>
+<style>
+:root { opacity: 0 }
+</style>
+A
+<textarea id="a" hidden=""></textarea>
+<object id="b" >
+A
+</html>

layout/painting/crashtests/crashtests.list

@@ -16,3 +16,4 @@ load 1468124-1.html
 load 1469472.html
 load 1477831-1.html
 load 1504033.html
+load 1514544-1.html