Bug 1286957 - Because combining touch-action areas into the event regions is fraught with peril, dump them into the dispatch-to-content region. r=tnikkel

MozReview-Commit-ID: FOyCEFP3Hw6

layout/base/FrameLayerBuilder.cpp

@@ -465,6 +465,11 @@ public:
                   LayerState aLayerState);
   AnimatedGeometryRoot* GetAnimatedGeometryRoot() { return mAnimatedGeometryRoot; }
 
+  /**
+   * A region including the horizontal pan, vertical pan, and no action regions.
+   */
+  nsRegion CombinedTouchActionRegion();
+
   /**
    * Add the given hit regions to the hit regions to the hit retions for this
    * PaintedLayer.
@@ -3243,6 +3248,12 @@ void ContainerState::FinishPaintedLayerData(PaintedLayerData& aData, FindOpaqueB
       &containingPaintedLayerData->mHitRegion,
       &containingPaintedLayerData->mMaybeHitRegion,
       &matrixCache);
+    // See the comment in nsDisplayList::AddFrame, where the touch action regions
+    // are handled. The same thing applies here.
+    bool alreadyHadRegions =
+        !containingPaintedLayerData->mNoActionRegion.IsEmpty() ||
+        !containingPaintedLayerData->mHorizontalPanRegion.IsEmpty() ||
+        !containingPaintedLayerData->mVerticalPanRegion.IsEmpty();
     nsLayoutUtils::TransformToAncestorAndCombineRegions(
       data->mNoActionRegion,
       mContainerReferenceFrame,
@@ -3264,7 +3275,10 @@ void ContainerState::FinishPaintedLayerData(PaintedLayerData& aData, FindOpaqueB
       &containingPaintedLayerData->mVerticalPanRegion,
       &containingPaintedLayerData->mDispatchToContentHitRegion,
       &matrixCache);
-
+    if (alreadyHadRegions) {
+      containingPaintedLayerData->mDispatchToContentHitRegion.OrWith(
+        containingPaintedLayerData->CombinedTouchActionRegion());
+    }
   } else {
     EventRegions regions;
     regions.mHitRegion = ScaleRegionToOutsidePixels(data->mHitRegion);
@@ -3461,17 +3475,35 @@ PaintedLayerData::Accumulate(ContainerState* aState,
   }
 }
 
+nsRegion
+PaintedLayerData::CombinedTouchActionRegion()
+{
+  nsRegion result;
+  result.Or(mHorizontalPanRegion, mVerticalPanRegion);
+  result.OrWith(mNoActionRegion);
+  return result;
+}
+
 void
 PaintedLayerData::AccumulateEventRegions(ContainerState* aState, nsDisplayLayerEventRegions* aEventRegions)
 {
   FLB_LOG_PAINTED_LAYER_DECISION(this, "Accumulating event regions %p against pld=%p\n", aEventRegions, this);
 
-  mHitRegion.Or(mHitRegion, aEventRegions->HitRegion());
-  mMaybeHitRegion.Or(mMaybeHitRegion, aEventRegions->MaybeHitRegion());
-  mDispatchToContentHitRegion.Or(mDispatchToContentHitRegion, aEventRegions->DispatchToContentHitRegion());
-  mNoActionRegion.Or(mNoActionRegion, aEventRegions->NoActionRegion());
-  mHorizontalPanRegion.Or(mHorizontalPanRegion, aEventRegions->HorizontalPanRegion());
-  mVerticalPanRegion.Or(mVerticalPanRegion, aEventRegions->VerticalPanRegion());
+  mHitRegion.OrWith(aEventRegions->HitRegion());
+  mMaybeHitRegion.OrWith(aEventRegions->MaybeHitRegion());
+  mDispatchToContentHitRegion.OrWith(aEventRegions->DispatchToContentHitRegion());
+
+  // See the comment in nsDisplayList::AddFrame, where the touch action regions
+  // are handled. The same thing applies here.
+  bool alreadyHadRegions = !mNoActionRegion.IsEmpty() ||
+      !mHorizontalPanRegion.IsEmpty() ||
+      !mVerticalPanRegion.IsEmpty();
+  mNoActionRegion.OrWith(aEventRegions->NoActionRegion());
+  mHorizontalPanRegion.OrWith(aEventRegions->HorizontalPanRegion());
+  mVerticalPanRegion.OrWith(aEventRegions->VerticalPanRegion());
+  if (alreadyHadRegions) {
+    mDispatchToContentHitRegion.OrWith(CombinedTouchActionRegion());
+  }
 
   // Calculate scaled versions of the bounds of mHitRegion and mMaybeHitRegion
   // for quick access in FindPaintedLayerFor().

layout/base/nsDisplayList.cpp

@@ -3676,14 +3676,31 @@ nsDisplayLayerEventRegions::AddFrame(nsDisplayListBuilder* aBuilder,
   // Touch action region
 
   uint32_t touchAction = nsLayoutUtils::GetTouchActionFromFrame(aFrame);
-  if (touchAction & NS_STYLE_TOUCH_ACTION_NONE) {
-    mNoActionRegion.Or(mNoActionRegion, borderBox);
-  } else {
-    if ((touchAction & NS_STYLE_TOUCH_ACTION_PAN_X)) {
-      mHorizontalPanRegion.Or(mHorizontalPanRegion, borderBox);
+  if (touchAction != NS_STYLE_TOUCH_ACTION_AUTO) {
+    // If this frame has touch-action areas, and there were already
+    // touch-action areas from some other element on this same event regions,
+    // then all we know is that there are multiple elements with touch-action
+    // properties. In particular, we don't know what the relationship is
+    // between those elements in terms of DOM ancestry, and so we don't know
+    // how to combine the regions properly. Instead, we just add all the areas
+    // to the dispatch-to-content region, so that the APZ knows to check with
+    // the main thread. XXX we need to come up with a better way to do this,
+    // see bug 1287829.
+    bool alreadyHadRegions = !mNoActionRegion.IsEmpty() ||
+        !mHorizontalPanRegion.IsEmpty() ||
+        !mVerticalPanRegion.IsEmpty();
+    if (touchAction & NS_STYLE_TOUCH_ACTION_NONE) {
+      mNoActionRegion.OrWith(borderBox);
+    } else {
+      if ((touchAction & NS_STYLE_TOUCH_ACTION_PAN_X)) {
+        mHorizontalPanRegion.OrWith(borderBox);
+      }
+      if ((touchAction & NS_STYLE_TOUCH_ACTION_PAN_Y)) {
+        mVerticalPanRegion.OrWith(borderBox);
+      }
     }
-    if ((touchAction & NS_STYLE_TOUCH_ACTION_PAN_Y)) {
-      mVerticalPanRegion.Or(mVerticalPanRegion, borderBox);
+    if (alreadyHadRegions) {
+      mDispatchToContentHitRegion.OrWith(CombinedTouchActionRegion());
     }
   }
 }
@@ -3710,6 +3727,15 @@ nsDisplayLayerEventRegions::IsEmpty() const
   return false;
 }
 
+nsRegion
+nsDisplayLayerEventRegions::CombinedTouchActionRegion()
+{
+  nsRegion result;
+  result.Or(mHorizontalPanRegion, mVerticalPanRegion);
+  result.OrWith(mNoActionRegion);
+  return result;
+}
+
 int32_t
 nsDisplayLayerEventRegions::ZIndex() const
 {

layout/base/nsDisplayList.h

@@ -3164,6 +3164,7 @@ public:
   const nsRegion& NoActionRegion() { return mNoActionRegion; }
   const nsRegion& HorizontalPanRegion() { return mHorizontalPanRegion; }
   const nsRegion& VerticalPanRegion() { return mVerticalPanRegion; }
+  nsRegion CombinedTouchActionRegion();
 
   virtual void WriteDebugInfo(std::stringstream& aStream) override;