Bug 1257641 - Use empty transactions to carry scroll offset updates to APZ that don't require a repaint. r=mattwoodrow,mstange,botond

MozReview-Commit-ID: KNeGSKldmp7

gfx/layers/FrameMetrics.h

@@ -26,6 +26,15 @@ template <typename T> struct ParamTraits;
 namespace mozilla {
 namespace layers {
 
+/**
+ * Helper struct to hold a couple of fields that can be updated as part of
+ * an empty transaction.
+ */
+struct ScrollUpdateInfo {
+  uint32_t mScrollGeneration;
+  CSSPoint mScrollOffset;
+};
+
 /**
  * The viewport and displayport metrics for the painted frame at the
  * time of a layer-tree transaction.  These metrics are especially
@@ -44,6 +53,9 @@ public:
   enum ScrollOffsetUpdateType : uint8_t {
     eNone,          // The default; the scroll offset was not updated
     eMainThread,    // The scroll offset was updated by the main thread.
+    ePending,       // The scroll offset was updated on the main thread, but not
+                    // painted, so the layer texture data is still at the old
+                    // offset.
 
     eSentinel       // For IPC use only
   };
@@ -241,6 +253,13 @@ public:
     mDoSmoothScroll = aOther.mDoSmoothScroll;
   }
 
+  void UpdatePendingScrollInfo(const ScrollUpdateInfo& aInfo)
+  {
+    mScrollOffset = aInfo.mScrollOffset;
+    mScrollGeneration = aInfo.mScrollGeneration;
+    mScrollUpdateType = ePending;
+  }
+
   void UpdateScrollInfo(uint32_t aScrollGeneration, const CSSPoint& aScrollOffset)
   {
     mScrollOffset = aScrollOffset;
@@ -380,6 +399,11 @@ public:
     mScrollGeneration = aScrollGeneration;
   }
 
+  ScrollOffsetUpdateType GetScrollUpdateType() const
+  {
+    return mScrollUpdateType;
+  }
+
   bool GetScrollOffsetUpdated() const
   {
     return mScrollUpdateType != eNone;

gfx/layers/Layers.cpp

@@ -567,6 +567,11 @@ Layer::ApplyPendingUpdatesToSubtree()
   for (Layer* child = GetFirstChild(); child; child = child->GetNextSibling()) {
     child->ApplyPendingUpdatesToSubtree();
   }
+  if (!GetParent()) {
+    // Once we're done recursing through the whole tree, clear the pending
+    // updates from the manager.
+    Manager()->ClearPendingScrollInfoUpdate();
+  }
 }
 
 bool
@@ -946,6 +951,15 @@ Layer::ApplyPendingUpdatesForThisTransaction()
     mPendingAnimations = nullptr;
     Mutated();
   }
+
+  for (size_t i = 0; i < mScrollMetadata.Length(); i++) {
+    FrameMetrics& fm = mScrollMetadata[i].GetMetrics();
+    Maybe<ScrollUpdateInfo> update = Manager()->GetPendingScrollInfoUpdate(fm.GetScrollId());
+    if (update) {
+      fm.UpdatePendingScrollInfo(update.value());
+      Mutated();
+    }
+  }
 }
 
 float
@@ -2446,6 +2460,29 @@ LayerManager::IsLogEnabled()
   return MOZ_LOG_TEST(GetLog(), LogLevel::Debug);
 }
 
+void
+LayerManager::SetPendingScrollUpdateForNextTransaction(FrameMetrics::ViewID aScrollId,
+                                                       const ScrollUpdateInfo& aUpdateInfo)
+{
+  mPendingScrollUpdates[aScrollId] = aUpdateInfo;
+}
+
+Maybe<ScrollUpdateInfo>
+LayerManager::GetPendingScrollInfoUpdate(FrameMetrics::ViewID aScrollId)
+{
+  auto it = mPendingScrollUpdates.find(aScrollId);
+  if (it != mPendingScrollUpdates.end()) {
+    return Some(it->second);
+  }
+  return Nothing();
+}
+
+void
+LayerManager::ClearPendingScrollInfoUpdate()
+{
+  mPendingScrollUpdates.clear();
+}
+
 void
 PrintInfo(std::stringstream& aStream, LayerComposite* aLayerComposite)
 {

gfx/layers/Layers.h

@@ -6,6 +6,7 @@
 #ifndef GFX_LAYERS_H
 #define GFX_LAYERS_H
 
+#include <map>
 #include <stdint.h>                     // for uint32_t, uint64_t, uint8_t
 #include <stdio.h>                      // for FILE
 #include <sys/types.h>                  // for int32_t, int64_t
@@ -698,6 +699,19 @@ private:
   FramesTimingRecording mRecording;
 
   TimeStamp mTabSwitchStart;
+
+public:
+  /*
+   * Methods to store/get/clear a "pending scroll info update" object on a
+   * per-scrollid basis. This is used for empty transactions that push over
+   * scroll position updates to the APZ code.
+   */
+  void SetPendingScrollUpdateForNextTransaction(FrameMetrics::ViewID aScrollId,
+                                                const ScrollUpdateInfo& aUpdateInfo);
+  Maybe<ScrollUpdateInfo> GetPendingScrollInfoUpdate(FrameMetrics::ViewID aScrollId);
+  void ClearPendingScrollInfoUpdate();
+private:
+  std::map<FrameMetrics::ViewID,ScrollUpdateInfo> mPendingScrollUpdates;
 };
 
 typedef InfallibleTArray<Animation> AnimationArray;
@@ -857,6 +871,7 @@ public:
    */
   void SetScrollMetadata(const ScrollMetadata& aScrollMetadata)
   {
+    Manager()->ClearPendingScrollInfoUpdate();
     if (mScrollMetadata.Length() != 1 || mScrollMetadata[0] != aScrollMetadata) {
       MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FrameMetrics", this));
       mScrollMetadata.ReplaceElementsAt(0, mScrollMetadata.Length(), aScrollMetadata);
@@ -884,6 +899,7 @@ public:
    */
   void SetScrollMetadata(const nsTArray<ScrollMetadata>& aMetadataArray)
   {
+    Manager()->ClearPendingScrollInfoUpdate();
     if (mScrollMetadata != aMetadataArray) {
       MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FrameMetrics", this));
       mScrollMetadata = aMetadataArray;

gfx/layers/LayersLogging.cpp

@@ -191,7 +191,7 @@ AppendToString(std::stringstream& aStream, const FrameMetrics& m,
     AppendToString(aStream, m.GetZoom(), " z=");
     AppendToString(aStream, m.GetExtraResolution(), " er=");
     aStream << nsPrintfCString(")] [u=(%d %d %lu)",
-            m.GetScrollOffsetUpdated(), m.GetDoSmoothScroll(),
+            m.GetScrollUpdateType(), m.GetDoSmoothScroll(),
             m.GetScrollGeneration()).get();
     AppendToString(aStream, m.GetScrollParentId(), "] [p=");
     aStream << nsPrintfCString("] [i=(%ld %lld %d)] }",

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -3388,7 +3388,9 @@ void AsyncPanZoomController::NotifyLayersUpdated(const ScrollMetadata& aScrollMe
     APZC_LOG("%p NotifyLayersUpdated short-circuit\n", this);
     return;
   }
-  mLastContentPaintMetrics = aLayerMetrics;
+  if (aLayerMetrics.GetScrollUpdateType() != FrameMetrics::ScrollOffsetUpdateType::ePending) {
+    mLastContentPaintMetrics = aLayerMetrics;
+  }
 
   mFrameMetrics.SetScrollParentId(aLayerMetrics.GetScrollParentId());
   APZC_LOG_FM(aLayerMetrics, "%p got a NotifyLayersUpdated with aIsFirstPaint=%d, aThisLayerTreeUpdated=%d",

layout/generic/nsGfxScrollFrame.cpp

@@ -66,7 +66,6 @@
 #include <mozilla/layers/AxisPhysicsMSDModel.h>
 #include "mozilla/layers/LayerTransactionChild.h"
 #include "mozilla/layers/ScrollLinkedEffectDetector.h"
-#include "mozilla/layers/ShadowLayers.h"
 #include "mozilla/unused.h"
 #include "LayersLogging.h"  // for Stringify
 #include <algorithm>
@@ -2752,14 +2751,18 @@ ScrollFrameHelper::ScrollToImpl(nsPoint aPt, const nsRect& aRange, nsIAtom* aOri
                  !content->GetComposedDoc()->HasScrollLinkedEffect()) {
         nsIWidget* widget = presContext->GetNearestWidget();
         LayerManager* manager = widget ? widget->GetLayerManager() : nullptr;
-        ShadowLayerForwarder* forwarder = manager ? manager->AsShadowForwarder() : nullptr;
-        if (forwarder && forwarder->HasShadowManager()) {
+        if (manager) {
           mozilla::layers::FrameMetrics::ViewID id;
           DebugOnly<bool> success = nsLayoutUtils::FindIDFor(content, &id);
           MOZ_ASSERT(success); // we have a displayport, we better have an ID
-          forwarder->GetShadowManager()->SendUpdateScrollOffset(id,
-              mScrollGeneration, CSSPoint::FromAppUnits(GetScrollPosition()));
+
+          // Schedule an empty transaction to carry over the scroll offset update,
+          // instead of a full transaction. This empty transaction might still get
+          // squashed into a full transaction if something happens to trigger one.
           schedulePaint = false;
+          manager->SetPendingScrollUpdateForNextTransaction(id,
+              { mScrollGeneration, CSSPoint::FromAppUnits(GetScrollPosition()) });
+          mOuter->SchedulePaint(nsIFrame::PAINT_COMPOSITE_ONLY);
           PAINT_SKIP_LOG("Skipping due to APZ-forwarded main-thread scroll\n");
         }
       }