Bug 1119497 - Don't continue searching if we hit a layer that has no containing APZC. r=botond

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -1373,7 +1373,7 @@ APZCTreeManager::GetAPZCAtPoint(HitTestingTreeNode* aNode,
     }
 
     // If we didn't match anything in the subtree, check |node|.
-    if (!result) {
+    if (*aOutHitResult == NoApzcHit) {
       APZCTM_LOG("Testing ParentLayer point %s (Layer %s) against node %p\n",
           Stringify(aHitTestPoint).c_str(),
           hitTestPointForChildLayers ? Stringify(hitTestPointForChildLayers.ref()).c_str() : "nil",
@@ -1392,14 +1392,14 @@ APZCTreeManager::GetAPZCAtPoint(HitTestingTreeNode* aNode,
     // If we are overscrolled, and the point matches us or one of our children,
     // the result is inside an overscrolled APZC, inform our caller of this
     // (callers typically ignore events targeted at overscrolled APZCs).
-    if (result && apzc && apzc->IsOverscrolled()) {
+    if (*aOutHitResult != NoApzcHit && apzc && apzc->IsOverscrolled()) {
       APZCTM_LOG("Result is inside overscrolled APZC %p\n", apzc);
       *aOutHitResult = OverscrolledApzc;
       return nullptr;
     }
 
-    if (result) {
-      if (!gfxPrefs::LayoutEventRegionsEnabled()) {
+    if (*aOutHitResult != NoApzcHit) {
+      if (result && !gfxPrefs::LayoutEventRegionsEnabled()) {
         // When event-regions are disabled, we treat scrollinfo layers as
         // regular scrollable layers. Unfortunately, their "hit region" (which
         // we create from the composition bounds) is their full area, and they

gfx/tests/gtest/TestAsyncPanZoomController.cpp

@@ -2551,6 +2551,25 @@ protected:
     manager->UpdateHitTestingTree(nullptr, root, false, 0, 0);
     rootApzc = ApzcOf(root);
   }
+
+  void CreateBug1119497LayerTree() {
+    const char* layerTreeSyntax = "c(tt)";
+    // LayerID                     0 12
+    // 0 is the root and doesn't have an APZC
+    // 1 is behind 2 and does have an APZC
+    // 2 entirely covers 1 and should take all the input events
+    nsIntRegion layerVisibleRegions[] = {
+      nsIntRegion(nsIntRect(0, 0, 100, 100)),
+      nsIntRegion(nsIntRect(0, 0, 100, 100)),
+      nsIntRegion(nsIntRect(0, 0, 100, 100)),
+    };
+    root = CreateLayerTree(layerTreeSyntax, layerVisibleRegions, nullptr, lm, layers);
+
+    SetScrollableFrameMetrics(layers[1], FrameMetrics::START_SCROLL_ID + 1);
+
+    registration = MakeUnique<ScopedLayerTreeRegistration>(0, root, mcc);
+    manager->UpdateHitTestingTree(nullptr, root, false, 0, 0);
+  }
 };
 
 TEST_F(APZEventRegionsTester, HitRegionImmediateResponse) {
@@ -2643,6 +2662,19 @@ TEST_F(APZEventRegionsTester, Obscuration) {
   EXPECT_EQ(HitTestResult::ApzcHitRegion, result);
 }
 
+TEST_F(APZEventRegionsTester, Bug1119497) {
+  SCOPED_GFX_PREF(LayoutEventRegionsEnabled, bool, true);
+
+  CreateBug1119497LayerTree();
+
+  HitTestResult result;
+  nsRefPtr<AsyncPanZoomController> hit = manager->GetTargetAPZC(ScreenPoint(50, 50), &result);
+  // We should hit layers[2], so |result| will be ApzcHitRegion but there's no
+  // actual APZC in that parent chain, so |hit| should be nullptr.
+  EXPECT_EQ(nullptr, hit.get());
+  EXPECT_EQ(HitTestResult::ApzcHitRegion, result);
+}
+
 class TaskRunMetrics {
 public:
   TaskRunMetrics()