Bug 1468545 - Add some logging for drag event handling. r=botond

I found this useful while debugging.

MozReview-Commit-ID: 1swqwStpAq0

--HG--
extra : rebase_source : 1731ed717a5446873439a0acc68abd14eb3d3590

gfx/layers/apz/src/AsyncPanZoomController.cpp

@@ -995,6 +995,7 @@ nsEventStatus AsyncPanZoomController::HandleDragEvent(const MouseInput& aEvent,
   }
 
   if (aEvent.mType == MouseInput::MouseType::MOUSE_UP) {
+    APZC_LOG("%p ending drag\n", this);
     SetState(NOTHING);
     ScrollSnap();
     return nsEventStatus_eConsumeNoDefault;
@@ -1003,14 +1004,17 @@ nsEventStatus AsyncPanZoomController::HandleDragEvent(const MouseInput& aEvent,
   HitTestingTreeNodeAutoLock node;
   GetApzcTreeManager()->FindScrollThumbNode(aDragMetrics, node);
   if (!node) {
+    APZC_LOG("%p unable to find scrollthumb node with viewid %" PRIu64 "\n", this, aDragMetrics.mViewId);
     return nsEventStatus_eConsumeNoDefault;
   }
 
   if (aEvent.mType == MouseInput::MouseType::MOUSE_DOWN) {
+    APZC_LOG("%p starting scrollbar drag\n", this);
     SetState(SCROLLBAR_DRAG);
   }
 
   if (aEvent.mType != MouseInput::MouseType::MOUSE_MOVE) {
+    APZC_LOG("%p discarding event of type %d\n", this, aEvent.mType);
     return nsEventStatus_eConsumeNoDefault;
   }
 
@@ -1035,6 +1039,7 @@ nsEventStatus AsyncPanZoomController::HandleDragEvent(const MouseInput& aEvent,
     // offscreen and its visible region is therefore empty.
     if (thumbWidth > 0 && thumbWidth * snapMultiplier < distance) {
       isMouseAwayFromThumb = true;
+      APZC_LOG("%p determined mouse is away from thumb, will snap\n", this);
     }
   }
 
@@ -1051,6 +1056,7 @@ nsEventStatus AsyncPanZoomController::HandleDragEvent(const MouseInput& aEvent,
   maxThumbPos -= scrollbarData.mThumbLength;
 
   float scrollPercent = thumbPosition / maxThumbPos;
+  APZC_LOG("%p scrollbar dragged to %f percent\n", this, scrollPercent);
 
   CSSCoord minScrollPosition =
     GetAxisStart(direction, mFrameMetrics.GetScrollableRect().TopLeft());
@@ -1068,6 +1074,7 @@ nsEventStatus AsyncPanZoomController::HandleDragEvent(const MouseInput& aEvent,
   } else {
     scrollOffset.y = scrollPosition;
   }
+  APZC_LOG("%p set scroll offset to %s from scrollbar drag\n", this, Stringify(scrollOffset).c_str());
   mFrameMetrics.SetScrollOffset(scrollOffset);
   ScheduleCompositeAndMaybeRepaint();
   UpdateSharedCompositorFrameMetrics();

gfx/layers/apz/src/InputQueue.cpp

@@ -703,13 +703,15 @@ InputQueue::SetConfirmedTargetApzc(uint64_t aInputBlockId, const RefPtr<AsyncPan
 }
 
 void
-InputQueue::ConfirmDragBlock(uint64_t aInputBlockId, const RefPtr<AsyncPanZoomController>& aTargetApzc,
-                                   const AsyncDragMetrics& aDragMetrics)
+InputQueue::ConfirmDragBlock(uint64_t aInputBlockId,
+                             const RefPtr<AsyncPanZoomController>& aTargetApzc,
+                             const AsyncDragMetrics& aDragMetrics)
 {
   APZThreadUtils::AssertOnControllerThread();
 
-  INPQ_LOG("got a target apzc; block=%" PRIu64 " guid=%s\n",
-    aInputBlockId, aTargetApzc ? Stringify(aTargetApzc->GetGuid()).c_str() : "");
+  INPQ_LOG("got a target apzc; block=%" PRIu64 " guid=%s dragtarget=%" PRIu64 "\n",
+    aInputBlockId, aTargetApzc ? Stringify(aTargetApzc->GetGuid()).c_str() : "",
+    aDragMetrics.mViewId);
   bool success = false;
   InputData* firstInput = nullptr;
   InputBlockState* inputBlock = FindBlockForId(aInputBlockId, &firstInput);