Bug 1468545 - Distinguish between upwards- and downwards-propagating information in InputAPZContext. r=botond

No functional changes here, but this updates the documentation in
InputAPZContext and separates the fields into two categories for easier
understanding. This is what I had in mind when I introduced this class
but never documented it anywhere, and so the "pending layerization" flag
didn't follow the convention that I had in mind. This cleans that up.

MozReview-Commit-ID: I26Ocu5Uco2

--HG--
extra : rebase_source : 8e0e096f6a98626624e3d62f89d0ffea2049cd8c

dom/ipc/TabChild.cpp

@@ -1727,10 +1727,7 @@ TabChild::HandleRealMouseButtonEvent(const WidgetMouseEvent& aEvent,
                                                         aInputBlockId);
   }
 
-  InputAPZContext context(aGuid, aInputBlockId, nsEventStatus_eIgnore);
-  if (pendingLayerization) {
-    InputAPZContext::SetPendingLayerization();
-  }
+  InputAPZContext context(aGuid, aInputBlockId, nsEventStatus_eIgnore, pendingLayerization);
 
   WidgetMouseEvent localEvent(aEvent);
   localEvent.mWidget = mPuppetWidget;

gfx/layers/apz/util/InputAPZContext.cpp

@@ -12,8 +12,8 @@ namespace layers {
 ScrollableLayerGuid InputAPZContext::sGuid;
 uint64_t InputAPZContext::sBlockId = 0;
 nsEventStatus InputAPZContext::sApzResponse = nsEventStatus_eIgnore;
-bool InputAPZContext::sRoutedToChildProcess = false;
 bool InputAPZContext::sPendingLayerization = false;
+bool InputAPZContext::sRoutedToChildProcess = false;
 
 /*static*/ ScrollableLayerGuid
 InputAPZContext::GetTargetLayerGuid()
@@ -33,41 +33,10 @@ InputAPZContext::GetApzResponse()
   return sApzResponse;
 }
 
-/*static*/ void
-InputAPZContext::SetRoutedToChildProcess()
+/*static*/ bool
+InputAPZContext::HavePendingLayerization()
 {
-  sRoutedToChildProcess = true;
-}
-
-/*static*/ void
-InputAPZContext::SetPendingLayerization()
-{
-  sPendingLayerization = true;
-}
-
-InputAPZContext::InputAPZContext(const ScrollableLayerGuid& aGuid,
-                                 const uint64_t& aBlockId,
-                                 const nsEventStatus& aApzResponse)
-  : mOldGuid(sGuid)
-  , mOldBlockId(sBlockId)
-  , mOldApzResponse(sApzResponse)
-  , mOldRoutedToChildProcess(sRoutedToChildProcess)
-  , mOldPendingLayerization(sPendingLayerization)
-{
-  sGuid = aGuid;
-  sBlockId = aBlockId;
-  sApzResponse = aApzResponse;
-  sRoutedToChildProcess = false;
-  sPendingLayerization = false;
-}
-
-InputAPZContext::~InputAPZContext()
-{
-  sGuid = mOldGuid;
-  sBlockId = mOldBlockId;
-  sApzResponse = mOldApzResponse;
-  sRoutedToChildProcess = mOldRoutedToChildProcess;
-  sPendingLayerization = mOldPendingLayerization;
+  return sPendingLayerization;
 }
 
 /*static*/ bool
@@ -76,10 +45,36 @@ InputAPZContext::WasRoutedToChildProcess()
   return sRoutedToChildProcess;
 }
 
-/*static*/ bool
-InputAPZContext::HavePendingLayerization()
+InputAPZContext::InputAPZContext(const ScrollableLayerGuid& aGuid,
+                                 const uint64_t& aBlockId,
+                                 const nsEventStatus& aApzResponse,
+                                 bool aPendingLayerization)
+  : mOldGuid(sGuid)
+  , mOldBlockId(sBlockId)
+  , mOldApzResponse(sApzResponse)
+  , mOldPendingLayerization(sPendingLayerization)
+  , mOldRoutedToChildProcess(sRoutedToChildProcess)
 {
-  return sPendingLayerization;
+  sGuid = aGuid;
+  sBlockId = aBlockId;
+  sApzResponse = aApzResponse;
+  sPendingLayerization = aPendingLayerization;
+  sRoutedToChildProcess = false;
+}
+
+InputAPZContext::~InputAPZContext()
+{
+  sGuid = mOldGuid;
+  sBlockId = mOldBlockId;
+  sApzResponse = mOldApzResponse;
+  sPendingLayerization = mOldPendingLayerization;
+  sRoutedToChildProcess = mOldRoutedToChildProcess;
+}
+
+/*static*/ void
+InputAPZContext::SetRoutedToChildProcess()
+{
+  sRoutedToChildProcess = true;
 }
 
 } // namespace layers

gfx/layers/apz/util/InputAPZContext.h

@@ -13,40 +13,56 @@
 namespace mozilla {
 namespace layers {
 
-// InputAPZContext is used to communicate the ScrollableLayerGuid,
-// input block ID, APZ response from nsIWidget to RenderFrameParent.
-// It is conceptually attached to any WidgetInputEvent
-// that has been processed by APZ directly from a widget.
+// InputAPZContext is used to communicate various pieces of information
+// around the codebase without having to plumb it through lots of functions
+// and codepaths. Conceptually it is attached to a WidgetInputEvent that is
+// relevant to APZ.
+//
+// There are two types of information bits propagated using this class. One
+// type is propagated "downwards" (from a process entry point like nsBaseWidget
+// or TabChild) into deeper code that is run during complicated operations
+// like event dispatch. The other type is information that is propagated
+// "upwards", from the deeper code back to the entry point.
 class MOZ_STACK_CLASS InputAPZContext
 {
 private:
+  // State that is propagated downwards from InputAPZContext creation into
+  // "deeper" code.
   static ScrollableLayerGuid sGuid;
   static uint64_t sBlockId;
   static nsEventStatus sApzResponse;
-  static bool sRoutedToChildProcess;
   static bool sPendingLayerization;
 
+  // State that is set in deeper code and propagated upwards.
+  static bool sRoutedToChildProcess;
+
 public:
+  // Functions to access downwards-propagated data
   static ScrollableLayerGuid GetTargetLayerGuid();
   static uint64_t GetInputBlockId();
   static nsEventStatus GetApzResponse();
-  static void SetRoutedToChildProcess();
-  static void SetPendingLayerization();
+  static bool HavePendingLayerization();
 
+  // Functions to access upwards-propagated data
+  static bool WasRoutedToChildProcess();
+
+  // Constructor sets the data to be propagated downwards
   InputAPZContext(const ScrollableLayerGuid& aGuid,
                   const uint64_t& aBlockId,
-                  const nsEventStatus& aApzResponse);
+                  const nsEventStatus& aApzResponse,
+                  bool aPendingLayerization = false);
   ~InputAPZContext();
 
-  static bool WasRoutedToChildProcess();
-  static bool HavePendingLayerization();
+  // Functions to set data to be propagated upwards
+  static void SetRoutedToChildProcess();
 
 private:
   ScrollableLayerGuid mOldGuid;
   uint64_t mOldBlockId;
   nsEventStatus mOldApzResponse;
-  bool mOldRoutedToChildProcess;
   bool mOldPendingLayerization;
+
+  bool mOldRoutedToChildProcess;
 };
 
 } // namespace layers