Bug 1638535. APZCTreeManager::SetTargetAPZC needs to make sure it uses a zoomable apzc if it's processing pinch gesture input. r=kats

Differential Revision: https://phabricator.services.mozilla.com/D75670

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -2398,6 +2398,11 @@ void APZCTreeManager::SetTargetAPZC(
     RefPtr<AsyncPanZoomController> apzc = GetTargetAPZC(aTargets[i]);
     target = GetZoomableTarget(target, apzc);
   }
+  if (InputBlockState* block = mInputQueue->GetBlockForId(aInputBlockId)) {
+    if (block->AsPinchGestureBlock() && aTargets.Length() == 1) {
+      target = FindZoomableApzc(target);
+    }
+  }
   mInputQueue->SetConfirmedTargetApzc(aInputBlockId, target);
 }
 

gfx/layers/apz/src/InputQueue.cpp

@@ -634,6 +634,10 @@ void InputQueue::ScheduleMainThreadTimeout(
   }
 }
 
+InputBlockState* InputQueue::GetBlockForId(uint64_t aInputBlockId) {
+  return FindBlockForId(aInputBlockId, nullptr);
+}
+
 InputBlockState* InputQueue::FindBlockForId(uint64_t aInputBlockId,
                                             InputData** aOutFirstInput) {
   for (const auto& queuedInput : mQueuedInputs) {

gfx/layers/apz/src/InputQueue.h

@@ -142,6 +142,8 @@ class InputQueue {
    */
   bool IsDragOnScrollbar(bool aOnScrollbar);
 
+  InputBlockState* GetBlockForId(uint64_t aInputBlockId);
+
  private:
   ~InputQueue();