Bug 1412112 - Cache the view id on the ASR to speed up the ViewIDForASR operation. r=mstange

This also moves the function from nsLayoutUtils to be a function on the
ASR itself, which seems more appropriate.

MozReview-Commit-ID: 88lUmYi80P0

--HG--
extra : rebase_source : 3f7e4f875c3267f9f4c5c67e720912ceedb25719

gfx/layers/wr/ScrollingLayersHelper.cpp

@@ -109,7 +109,7 @@ ScrollingLayersHelper::BeginItem(nsDisplayItem* aItem,
 
   FrameMetrics::ViewID leafmostId = ids.first.valueOr(FrameMetrics::NULL_SCROLL_ID);
   FrameMetrics::ViewID scrollId = aItem->GetActiveScrolledRoot()
-      ? nsLayoutUtils::ViewIDForASR(aItem->GetActiveScrolledRoot())
+      ? aItem->GetActiveScrolledRoot()->GetViewId()
       : FrameMetrics::NULL_SCROLL_ID;
   // If the leafmost ASR is not the same as the item's ASR then we are dealing
   // with a case where the item's clip chain is scrolled by something other than
@@ -237,7 +237,7 @@ ScrollingLayersHelper::RecurseAndDefineClip(nsDisplayItem* aItem,
   if (ids.second) {
     // If we've already got an id for this clip, we can early-exit
     if (aAsr) {
-      FrameMetrics::ViewID scrollId = nsLayoutUtils::ViewIDForASR(aAsr);
+      FrameMetrics::ViewID scrollId = aAsr->GetViewId();
       MOZ_ASSERT(mBuilder->IsScrollLayerDefined(scrollId));
       ids.first = Some(scrollId);
     }
@@ -276,7 +276,7 @@ ScrollingLayersHelper::RecurseAndDefineClip(nsDisplayItem* aItem,
     }
   } else {
     MOZ_ASSERT(!ancestorIds.second);
-    FrameMetrics::ViewID scrollId = aChain->mASR ? nsLayoutUtils::ViewIDForASR(aChain->mASR) : FrameMetrics::NULL_SCROLL_ID;
+    FrameMetrics::ViewID scrollId = aChain->mASR ? aChain->mASR->GetViewId() : FrameMetrics::NULL_SCROLL_ID;
     if (mBuilder->TopmostScrollId() == scrollId) {
       if (mBuilder->TopmostIsClip()) {
         // If aChain->mASR is already the topmost scroll layer on the stack, but
@@ -344,7 +344,7 @@ ScrollingLayersHelper::RecurseAndDefineAsr(nsDisplayItem* aItem,
   // This will hold our return value
   std::pair<Maybe<FrameMetrics::ViewID>, Maybe<wr::WrClipId>> ids;
 
-  FrameMetrics::ViewID scrollId = nsLayoutUtils::ViewIDForASR(aAsr);
+  FrameMetrics::ViewID scrollId = aAsr->GetViewId();
   if (mBuilder->IsScrollLayerDefined(scrollId)) {
     // If we've already defined this scroll layer before, we can early-exit
     ids.first = Some(scrollId);

gfx/layers/wr/WebRenderScrollData.cpp

@@ -54,7 +54,7 @@ WebRenderLayerScrollData::Initialize(WebRenderScrollData& aOwner,
        asr && asr != aStopAtAsr;
        asr = asr->mParent) {
     MOZ_ASSERT(aOwner.GetManager());
-    FrameMetrics::ViewID scrollId = nsLayoutUtils::ViewIDForASR(asr);
+    FrameMetrics::ViewID scrollId = asr->GetViewId();
     if (Maybe<size_t> index = aOwner.HasMetadataFor(scrollId)) {
       mScrollIds.AppendElement(index.ref());
     } else {

layout/base/nsLayoutUtils.cpp

@@ -868,13 +868,6 @@ nsLayoutUtils::FindContentFor(ViewID aId)
   }
 }
 
-ViewID
-nsLayoutUtils::ViewIDForASR(const mozilla::ActiveScrolledRoot* aASR)
-{
-  nsIContent* content = aASR->mScrollableFrame->GetScrolledFrame()->GetContent();
-  return nsLayoutUtils::FindOrCreateIDFor(content);
-}
-
 nsIFrame*
 GetScrollFrameFromContent(nsIContent* aContent)
 {

layout/base/nsLayoutUtils.h

@@ -186,12 +186,6 @@ public:
    */
   static nsIContent* FindContentFor(ViewID aId);
 
-  /**
-   * Find the view ID (or generate a new one) for the content element
-   * corresponding to the ASR.
-   */
-  static ViewID ViewIDForASR(const mozilla::ActiveScrolledRoot* aASR);
-
   /**
    * Find the scrollable frame for a given ID.
    */

layout/painting/FrameLayerBuilder.cpp

@@ -5037,7 +5037,7 @@ FixUpFixedPositionLayer(Layer* aLayer,
   if (compositorASR && aTargetASR != compositorASR) {
     // Mark this layer as fixed with respect to the child scroll frame of aTargetASR.
     aLayer->SetFixedPositionData(
-      nsLayoutUtils::ViewIDForASR(FindDirectChildASR(aTargetASR, compositorASR)),
+      FindDirectChildASR(aTargetASR, compositorASR)->GetViewId(),
       aLayer->GetFixedPositionAnchor(),
       aLayer->GetFixedPositionSides());
   } else {

layout/painting/nsDisplayList.cpp

@@ -4905,7 +4905,7 @@ nsDisplayCompositorHitTestInfo::CreateWebRenderCommands(mozilla::wr::DisplayList
   // this display item).
   FrameMetrics::ViewID scrollId = FrameMetrics::NULL_SCROLL_ID;
   if (const ActiveScrolledRoot* asr = GetActiveScrolledRoot()) {
-    scrollId = nsLayoutUtils::ViewIDForASR(asr);
+    scrollId = asr->GetViewId();
   }
 
   // Insert a transparent rectangle with the hit-test info

layout/painting/nsDisplayList.h

@@ -262,6 +262,7 @@ struct ActiveScrolledRoot {
     }
     asr->mParent = aParent;
     asr->mScrollableFrame = aScrollableFrame;
+    asr->mViewId = Nothing();
     asr->mDepth = aParent ? aParent->mDepth + 1 : 1;
     asr->mRetained = aIsRetained;
 
@@ -290,6 +291,18 @@ struct ActiveScrolledRoot {
   // Call this when inserting an ancestor.
   void IncrementDepth() { mDepth++; }
 
+  /**
+   * Find the view ID (or generate a new one) for the content element
+   * corresponding to the ASR.
+   */
+  mozilla::layers::FrameMetrics::ViewID GetViewId() const {
+    if (!mViewId.isSome()) {
+      nsIContent* content = mScrollableFrame->GetScrolledFrame()->GetContent();
+      mViewId = Some(nsLayoutUtils::FindOrCreateIDFor(content));
+    }
+    return *mViewId;
+  }
+
   RefPtr<const ActiveScrolledRoot> mParent;
   nsIScrollableFrame* mScrollableFrame;
 
@@ -319,6 +332,11 @@ private:
     return aActiveScrolledRoot ? aActiveScrolledRoot->mDepth : 0;
   }
 
+  // This field is lazily populated in GetViewId(). We don't want to do the
+  // work of populating if webrender is disabled, because it is often not
+  // needed.
+  mutable Maybe<mozilla::layers::FrameMetrics::ViewID> mViewId;
+
   uint32_t mDepth;
   bool mRetained;
 };