Bug 1570124 - Enable mouse scrolling in FxR window r=masayuki

This change addresses two issues with vrhost sending WM_MOUSEWHEEL events:
- The point from the message had an incorrect coordinate origin. Documentation specifices that it should be screen, rather than window/client, origin. Since vrhost only knows about a position in the window, it translates the point before sending the message.
- Gecko ignores the point passed in to the window message and instead uses the point from GetMessagePos. As warnings indicate, this can be incorrect, as is exposed with vrhost. This change now uses this point from the message when available.

Differential Revision: https://phabricator.services.mozilla.com/D51322

gfx/vr/vrhost/vrhostapi.cpp

@@ -280,10 +280,21 @@ void SendUIMessageToVRWindow(uint32_t nVRWindowID, uint32_t msg,
   HWND hwnd = VRWindowManager::GetManager()->GetHWND(nVRWindowID);
   if (hwnd != nullptr) {
     switch (msg) {
+      case WM_MOUSEWHEEL:
+        // For MOUSEWHEEL, the coordinates are supposed to be at Screen origin
+        // rather than window client origin.
+        // Make the conversion to screen coordinates before posting the message
+        // to the Fx window.
+        POINT pt;
+        POINTSTOPOINT(pt, MAKEPOINTS(lparam));
+        if (!::ClientToScreen(hwnd, &pt)) {
+          break;
+        }
+        // otherwise, fallthrough
+        lparam = POINTTOPOINTS(pt);
       case WM_MOUSEMOVE:
       case WM_LBUTTONDOWN:
       case WM_LBUTTONUP:
-      case WM_MOUSEWHEEL:
       case WM_CHAR:
       case WM_KEYDOWN:
       case WM_KEYUP:

gfx/vr/vrhost/vrhosttest.cpp

@@ -331,10 +331,24 @@ void TestCreateVRWindow() {
     printf(
         "5. Simulating clicking outside the URL bar, which should "
         "send a keyboard blur event\n");
-    pt.x = 80;
+    pt.x = 20;
+    pt.y = 20;
     fnSendMsg(windowId, WM_LBUTTONDOWN, 0, POINTTOPOINTS(pt));
     fnSendMsg(windowId, WM_LBUTTONUP, 0, POINTTOPOINTS(pt));
 
+    ::Sleep(1000);
+
+    printf("6. Simulating scrolling the web content down and then up\n");
+
+    pt.x = 100;
+    pt.y = 100;
+    for (int i = -20; i < 10; ++i) {
+      fnSendMsg(windowId, WM_MOUSEWHEEL,
+                MAKELONG(0, (i < 0) ? -WHEEL_DELTA : WHEEL_DELTA),
+                POINTTOPOINTS(pt));
+      ::Sleep(100);
+    }
+
     ::Sleep(5000);
 
     // Close the Firefox VR Window

modules/libpref/init/StaticPrefList.yaml

@@ -6445,6 +6445,13 @@
   value: 1500
   mirror: always
 
+# Mouse wheel scroll position is determined by GetMessagePos rather than
+# LPARAM msg value
+- name: mousewheel.ignore_cursor_position_in_lparam
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
 #---------------------------------------------------------------------------
 # Prefs starting with "network."
 #---------------------------------------------------------------------------

widget/windows/WinMouseScrollHandler.cpp

@@ -20,6 +20,7 @@
 #include "mozilla/MouseEvents.h"
 #include "mozilla/Preferences.h"
 #include "mozilla/dom/WheelEventBinding.h"
+#include "mozilla/StaticPrefs_mousewheel.h"
 
 #include <psapi.h>
 
@@ -303,21 +304,28 @@ nsresult MouseScrollHandler::SynthesizeNativeMouseScrollEvent(
 
 /* static */
 void MouseScrollHandler::InitEvent(nsWindowBase* aWidget,
-                                   WidgetGUIEvent& aEvent,
-                                   LayoutDeviceIntPoint* aPoint) {
+                                   WidgetGUIEvent& aEvent, LPARAM* aPoint) {
   NS_ENSURE_TRUE_VOID(aWidget);
-  LayoutDeviceIntPoint point;
-  if (aPoint) {
-    point = *aPoint;
+
+  // If a point is provided, use it; otherwise, get current message point or
+  // synthetic point
+  POINTS pointOnScreen;
+  if (aPoint != nullptr) {
+    pointOnScreen = MAKEPOINTS(*aPoint);
   } else {
-    POINTS pts = GetCurrentMessagePos();
-    POINT pt;
-    pt.x = pts.x;
-    pt.y = pts.y;
-    ::ScreenToClient(aWidget->GetWindowHandle(), &pt);
-    point.x = pt.x;
-    point.y = pt.y;
+    pointOnScreen = GetCurrentMessagePos();
   }
+
+  // InitEvent expects the point to be in window coordinates, so translate the
+  // point from screen coordinates.
+  POINT pointOnWindow;
+  POINTSTOPOINT(pointOnWindow, pointOnScreen);
+  ::ScreenToClient(aWidget->GetWindowHandle(), &pointOnWindow);
+
+  LayoutDeviceIntPoint point;
+  point.x = pointOnWindow.x;
+  point.y = pointOnWindow.y;
+
   aWidget->InitEvent(aEvent, &point);
 }
 
@@ -622,7 +630,8 @@ void MouseScrollHandler::HandleMouseWheelMessage(nsWindowBase* aWidget,
   RefPtr<nsWindowBase> kungFuDethGrip(aWidget);
 
   WidgetWheelEvent wheelEvent(true, eWheel, aWidget);
-  if (mLastEventInfo.InitWheelEvent(aWidget, wheelEvent, modKeyState)) {
+  if (mLastEventInfo.InitWheelEvent(aWidget, wheelEvent, modKeyState,
+                                    aLParam)) {
     MOZ_LOG(gMouseScrollLog, LogLevel::Info,
             ("MouseScroll::HandleMouseWheelMessage: dispatching "
              "eWheel event"));
@@ -680,10 +689,12 @@ void MouseScrollHandler::HandleScrollMessageAsMouseWheelMessage(
       return;
   }
   modKeyState.InitInputEvent(wheelEvent);
-  // XXX Current mouse position may not be same as when the original message
-  //     is received.  We need to know the actual mouse cursor position when
-  //     the original message was received.
-  InitEvent(aWidget, wheelEvent);
+
+  // Current mouse position may not be same as when the original message
+  // is received. However, this data is not available with the original
+  // message, which is why nullptr is passed in. We need to know the actual
+  // mouse cursor position when the original message was received.
+  InitEvent(aWidget, wheelEvent, nullptr);
 
   MOZ_LOG(
       gMouseScrollLog, LogLevel::Info,
@@ -789,13 +800,14 @@ int32_t MouseScrollHandler::LastEventInfo::RoundDelta(double aDelta) {
 
 bool MouseScrollHandler::LastEventInfo::InitWheelEvent(
     nsWindowBase* aWidget, WidgetWheelEvent& aWheelEvent,
-    const ModifierKeyState& aModKeyState) {
+    const ModifierKeyState& aModKeyState, LPARAM aLParam) {
   MOZ_ASSERT(aWheelEvent.mMessage == eWheel);
 
-  // XXX Why don't we use lParam value? We should use lParam value because
-  //     our internal message is always posted by original message handler.
-  //     So, GetMessagePos() may return different cursor position.
-  InitEvent(aWidget, aWheelEvent);
+  if (StaticPrefs::mousewheel_ignore_cursor_position_in_lparam()) {
+    InitEvent(aWidget, aWheelEvent, nullptr);
+  } else {
+    InitEvent(aWidget, aWheelEvent, &aLParam);
+  }
 
   aModKeyState.InitInputEvent(aWheelEvent);
 
@@ -1324,7 +1336,11 @@ bool MouseScrollHandler::Device::Elantech::HandleKeyMessage(
       WidgetCommandEvent appCommandEvent(
           true, (aWParam == VK_NEXT) ? nsGkAtoms::Forward : nsGkAtoms::Back,
           aWidget);
-      InitEvent(aWidget, appCommandEvent);
+
+      // In this scenario, the coordinate of the event isn't supplied, so pass
+      // nullptr as an argument to indicate using the coordinate from the last
+      // available window message.
+      InitEvent(aWidget, appCommandEvent, nullptr);
       aWidget->DispatchWindowEvent(&appCommandEvent);
     } else {
       MOZ_LOG(gMouseScrollLog, LogLevel::Info,

widget/windows/WinMouseScrollHandler.h

@@ -69,7 +69,7 @@ class MouseScrollHandler {
    * GetCurrentMessagePos() will be used.
    */
   static void InitEvent(nsWindowBase* aWidget, WidgetGUIEvent& aEvent,
-                        LayoutDeviceIntPoint* aPoint = nullptr);
+                        LPARAM* aPoint);
 
   /**
    * GetModifierKeyState() returns current modifier key state.
@@ -236,7 +236,7 @@ class MouseScrollHandler {
      *                          Otherwise, FALSE.
      */
     bool InitWheelEvent(nsWindowBase* aWidget, WidgetWheelEvent& aWheelEvent,
-                        const ModifierKeyState& aModKeyState);
+                        const ModifierKeyState& aModKeyState, LPARAM aLParam);
 
    private:
     static int32_t RoundDelta(double aDelta);