Bug 1405359 - Replace the mPushed* variables with a more encapsulated struct. r=jrmuizel

Storing the per-item clip state in a struct like this will allow us to
easily compare the desired clip state across items, so we can avoid
doing unnecessary work when going from one item to the next. This patch
has no functional changes, it's just refactoring.

MozReview-Commit-ID: 49B6hmsWZ4V

--HG--
extra : rebase_source : 8ac4bbf039f81bc2d26e92924ed041fa3d18e5ba

gfx/layers/wr/ScrollingLayersHelper.cpp

@@ -19,7 +19,6 @@ ScrollingLayersHelper::ScrollingLayersHelper(nsDisplayItem* aItem,
                                              WebRenderCommandBuilder::ClipIdMap& aCache,
                                              bool aApzEnabled)
   : mBuilder(&aBuilder)
-  , mPushedClipAndScroll(false)
   , mCache(aCache)
 {
   int32_t auPerDevPixel = aItem->Frame()->PresContext()->AppUnitsPerDevPixel();
@@ -63,23 +62,28 @@ ScrollingLayersHelper::ScrollingLayersHelper(nsDisplayItem* aItem,
   // the scroll stack
   if (!needClipAndScroll && mBuilder->TopmostScrollId() != scrollId) {
     MOZ_ASSERT(leafmostId == scrollId); // because !needClipAndScroll
-    mBuilder->PushScrollLayer(scrollId);
-    mPushedClips.push_back(wr::ScrollOrClipId(scrollId));
+    mItemClips.mScrollId = Some(scrollId);
   }
   // And ensure the leafmost clip, if scrolled by that ASR, is at the top of the
   // stack.
   if (ids.second && aItem->GetClipChain()->mASR == leafmostASR) {
-    mBuilder->PushClip(ids.second.ref());
-    mPushedClips.push_back(wr::ScrollOrClipId(ids.second.ref()));
+    mItemClips.mClipId = ids.second;
   }
   // If we need the ClipAndScroll, we want to replace the topmost scroll layer
   // with the item's ASR but preseve the topmost clip (which is scrolled by
   // some other ASR).
   if (needClipAndScroll) {
-    Maybe<wr::WrClipId> clipId = mBuilder->TopmostClipId();
-    mBuilder->PushClipAndScrollInfo(scrollId, clipId.ptrOr(nullptr));
-    mPushedClipAndScroll = true;
+    // If mClipId is set that means we want to push it such that it's going
+    // to be the TopmostClipId(), but we haven't actually pushed it yet.
+    // But we still want to take that instead of the actual current TopmostClipId().
+    Maybe<wr::WrClipId> clipId = mItemClips.mClipId;
+    if (!clipId) {
+      clipId = mBuilder->TopmostClipId();
+    }
+    mItemClips.mClipAndScroll = Some(std::make_pair(scrollId, clipId));
   }
+
+  mItemClips.Apply(mBuilder);
 }
 
 std::pair<Maybe<FrameMetrics::ViewID>, Maybe<wr::WrClipId>>
@@ -352,18 +356,35 @@ ScrollingLayersHelper::RecurseAndDefineAsr(nsDisplayItem* aItem,
 
 ScrollingLayersHelper::~ScrollingLayersHelper()
 {
-  if (mPushedClipAndScroll) {
-    mBuilder->PopClipAndScrollInfo();
+  mItemClips.Unapply(mBuilder);
+}
+
+void
+ScrollingLayersHelper::ItemClips::Apply(wr::DisplayListBuilder* aBuilder)
+{
+  if (mScrollId) {
+    aBuilder->PushScrollLayer(mScrollId.ref());
   }
-  while (!mPushedClips.empty()) {
-    wr::ScrollOrClipId id = mPushedClips.back();
-    if (id.is<wr::WrClipId>()) {
-      mBuilder->PopClip();
-    } else {
-      MOZ_ASSERT(id.is<FrameMetrics::ViewID>());
-      mBuilder->PopScrollLayer();
-    }
-    mPushedClips.pop_back();
+  if (mClipId) {
+    aBuilder->PushClip(mClipId.ref());
+  }
+  if (mClipAndScroll) {
+    aBuilder->PushClipAndScrollInfo(mClipAndScroll->first,
+                                    mClipAndScroll->second.ptrOr(nullptr));
+  }
+}
+
+void
+ScrollingLayersHelper::ItemClips::Unapply(wr::DisplayListBuilder* aBuilder)
+{
+  if (mClipAndScroll) {
+    aBuilder->PopClipAndScrollInfo();
+  }
+  if (mClipId) {
+    aBuilder->PopClip();
+  }
+  if (mScrollId) {
+    aBuilder->PopScrollLayer();
   }
 }
 

gfx/layers/wr/ScrollingLayersHelper.h

@@ -55,9 +55,18 @@ private:
                       const StackingContextHelper& aSc);
 
   wr::DisplayListBuilder* mBuilder;
-  bool mPushedClipAndScroll;
-  std::vector<wr::ScrollOrClipId> mPushedClips;
   WebRenderCommandBuilder::ClipIdMap& mCache;
+
+  struct ItemClips {
+    Maybe<FrameMetrics::ViewID> mScrollId;
+    Maybe<wr::WrClipId> mClipId;
+    Maybe<std::pair<FrameMetrics::ViewID, Maybe<wr::WrClipId>>> mClipAndScroll;
+
+    void Apply(wr::DisplayListBuilder* aBuilder);
+    void Unapply(wr::DisplayListBuilder* aBuilder);
+  };
+
+  ItemClips mItemClips;
 };
 
 } // namespace layers