Bug 1357754 - Record the isFirstPaint flag in the WebRenderScrollData. r=jrmuizel

MozReview-Commit-ID: KKiRBLRTfEj

gfx/layers/wr/WebRenderLayerManager.cpp

@@ -238,6 +238,7 @@ WebRenderLayerManager::WebRenderLayerManager(nsIWidget* aWidget)
   : mWidget(aWidget)
   , mLatestTransactionId(0)
   , mNeedsComposite(false)
+  , mIsFirstPaint(false)
   , mTarget(nullptr)
 {
   MOZ_COUNT_CTOR(WebRenderLayerManager);
@@ -403,8 +404,14 @@ WebRenderLayerManager::EndTransactionInternal(DrawPaintedLayerCallback aCallback
   }
 
   WebRenderScrollData scrollData;
-  if (mRoot && mWidget->AsyncPanZoomEnabled()) {
-    PopulateScrollData(scrollData, mRoot.get());
+  if (mWidget->AsyncPanZoomEnabled()) {
+    if (mIsFirstPaint) {
+      scrollData.SetIsFirstPaint();
+      mIsFirstPaint = false;
+    }
+    if (mRoot) {
+      PopulateScrollData(scrollData, mRoot.get());
+    }
   }
 
   bool sync = mTarget != nullptr;

gfx/layers/wr/WebRenderLayerManager.h

@@ -143,6 +143,7 @@ public:
     mNeedsComposite = aNeedsComposite;
   }
   virtual bool NeedsComposite() const override { return mNeedsComposite; }
+  virtual void SetIsFirstPaint() override { mIsFirstPaint = true; }
 
   DrawPaintedLayerCallback GetPaintedLayerCallback() const
   { return mPaintedLayerCallback; }
@@ -212,6 +213,7 @@ private:
   bool mTransactionIncomplete;
 
   bool mNeedsComposite;
+  bool mIsFirstPaint;
 
  // When we're doing a transaction in order to draw to a non-default
  // target, the layers transaction is only performed in order to send

gfx/layers/wr/WebRenderScrollData.cpp

@@ -74,6 +74,7 @@ WebRenderLayerScrollData::GetScrollMetadata(const WebRenderScrollData& aOwner,
 }
 
 WebRenderScrollData::WebRenderScrollData()
+  : mIsFirstPaint(false)
 {
 }
 
@@ -133,5 +134,17 @@ WebRenderScrollData::GetScrollMetadata(size_t aIndex) const
   return mScrollMetadatas[aIndex];
 }
 
+void
+WebRenderScrollData::SetIsFirstPaint()
+{
+  mIsFirstPaint = true;
+}
+
+bool
+WebRenderScrollData::IsFirstPaint() const
+{
+  return mIsFirstPaint;
+}
+
 } // namespace layers
 } // namespace mozilla

gfx/layers/wr/WebRenderScrollData.h

@@ -116,6 +116,9 @@ public:
 
   const ScrollMetadata& GetScrollMetadata(size_t aIndex) const;
 
+  void SetIsFirstPaint();
+  bool IsFirstPaint() const;
+
   friend struct IPC::ParamTraits<WebRenderScrollData>;
 
 private:
@@ -138,6 +141,8 @@ private:
   // descendants that layer had, which allows reconstructing the traversal on the
   // other side.
   nsTArray<WebRenderLayerScrollData> mLayerScrollData;
+
+  bool mIsFirstPaint;
 };
 
 } // namespace layers
@@ -197,13 +202,15 @@ struct ParamTraits<mozilla::layers::WebRenderScrollData>
   {
     WriteParam(aMsg, aParam.mScrollMetadatas);
     WriteParam(aMsg, aParam.mLayerScrollData);
+    WriteParam(aMsg, aParam.mIsFirstPaint);
   }
 
   static bool
   Read(const Message* aMsg, PickleIterator* aIter, paramType* aResult)
   {
     return ReadParam(aMsg, aIter, &aResult->mScrollMetadatas)
-        && ReadParam(aMsg, aIter, &aResult->mLayerScrollData);
+        && ReadParam(aMsg, aIter, &aResult->mLayerScrollData)
+        && ReadParam(aMsg, aIter, &aResult->mIsFirstPaint);
   }
 };