Bug 1541644 - Add some more logging statements. r=botond

Differential Revision: https://phabricator.services.mozilla.com/D26924

--HG--
extra : moz-landing-system : lando

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -11,6 +11,7 @@
 #include "Compositor.h"                     // for Compositor
 #include "DragTracker.h"                    // for DragTracker
 #include "gfxPrefs.h"                       // for gfxPrefs
+#include "GenericFlingAnimation.h"          // for FLING_LOG
 #include "HitTestingTreeNode.h"             // for HitTestingTreeNode
 #include "InputBlockState.h"                // for InputBlockState
 #include "InputData.h"                      // for InputData, etc
@@ -2374,6 +2375,7 @@ ParentLayerPoint APZCTreeManager::DispatchFling(
   // single APZC that's scrolled by the input block that triggered this fling.
   if (aHandoffState.mIsHandoff && !gfxPrefs::APZAllowImmediateHandoff() &&
       aHandoffState.mScrolledApzc == aPrev) {
+    FLING_LOG("APZCTM dropping handoff due to disallowed immediate handoff\n");
     return aHandoffState.mVelocity;
   }
 

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -2258,6 +2258,7 @@ bool AsyncPanZoomController::AllowScrollHandoffInCurrentBlock() const {
       // Do not allow handoff beyond the first APZC to scroll.
       if (currentBlock->GetScrolledApzc() == this) {
         result = false;
+        APZC_LOG("%p dropping handoff; AllowImmediateHandoff=false\n", this);
       }
     }
   }
@@ -3336,6 +3337,8 @@ void AsyncPanZoomController::HandleFlingOverscroll(
                                          true /* handoff */, aScrolledApzc};
     ParentLayerPoint residualVelocity =
         treeManagerLocal->DispatchFling(this, handoffState);
+    FLING_LOG("APZC %p left with residual velocity %s\n", this,
+        Stringify(residualVelocity).c_str());
     if (!IsZero(residualVelocity) && IsPannable() &&
         gfxPrefs::APZOverscrollEnabled()) {
       // Obey overscroll-behavior.

gfx/layers/apz/src/Axis.cpp

@@ -65,9 +65,13 @@ void Axis::UpdateWithTouchAtDevicePoint(ParentLayerCoord aPos,
 
   mPos = aPos;
 
+  AXIS_LOG("%p|%s got position %f\n", mAsyncPanZoomController, Name(),
+      mPos.value);
   if (Maybe<float> newVelocity =
           mVelocityTracker->AddPosition(aPos, aTimestampMs)) {
     mVelocity = mAxisLocked ? 0 : *newVelocity;
+    AXIS_LOG("%p|%s velocity from tracker is %f\n", mAsyncPanZoomController,
+        Name(), mVelocity);
   }
 }
 

gfx/layers/apz/src/GenericFlingAnimation.h

@@ -12,6 +12,7 @@
 #include "AsyncPanZoomController.h"
 #include "FrameMetrics.h"
 #include "Layers.h"
+#include "LayersLogging.h"
 #include "Units.h"
 #include "OverscrollHandoffState.h"
 #include "gfxPrefs.h"