Ensure that trackpad and trackpoint scrolling works on Windows desktop Aura with legacy trackpad dr…

ui/views/win/hwnd_message_handler.cc

Index: ui/views/win/hwnd_message_handler.cc
===================================================================
--- ui/views/win/hwnd_message_handler.cc	(revision 243629)
+++ ui/views/win/hwnd_message_handler.cc	(working copy)
@@ -299,6 +299,24 @@
 // The thickness of an auto-hide taskbar in pixels.
 const int kAutoHideTaskbarThicknessPx = 2;
 
+bool IsTopLevelWindow(HWND window) {
+  long style = GetWindowLong(window, GWL_STYLE);
+  if (!(style & WS_CHILD))
+    return true;
+
+  HWND parent = GetParent(window);
+  return !parent || (parent == GetDesktopWindow());
+}
+
+void AddScrollStylesToWindow(HWND window) {
+  if (::IsWindow(window)) {
+    DCHECK(IsTopLevelWindow(window));
+    long current_style = ::GetWindowLong(window, GWL_STYLE);
+    ::SetWindowLong(window, GWL_STYLE,
+                    current_style | WS_VSCROLL | WS_HSCROLL);
+  }
+}
+
 }  // namespace
 
 // A scoping class that prevents a window from being able to redraw in response
@@ -1343,6 +1361,21 @@
 
   delegate_->HandleCreate();
 
+#if defined(USE_AURA)

[sky, 2014/01/10 16:43:21]

Can this be moved to CalculateWindowStylesFromInitParams and passed in so that
we don't have to check each time if we should add/remove the style?

[ananta, 2014/01/10 18:59:21]

Done.

+  // Certain trackpad drivers on Windows have bugs where in they don't generate
+  // WM_MOUSEWHEEL messages for the trackpoint and trackpad scrolling gestures
+  // unless there is an entry for Chrome with the class name of the Window.
+  // These drivers check if the window under the trackpoint has the WS_VSCROLL/
+  // WS_HSCROLL style and if yes they generate the legacy WM_VSCROLL/WM_HSCROLL
+  // messages. We want the style to be present on the window. However we don't
+  // want Windows to draw the scrollbars. To achieve this we hide the scroll
+  // bars and readd them to the window style in a posted task which works.
+  if (IsTopLevelWindow(hwnd())) {
+    long current_style = ::GetWindowLong(hwnd(), GWL_STYLE);
+    ::SetWindowLong(hwnd(), GWL_STYLE,
+                    current_style | WS_VSCROLL | WS_HSCROLL);
+  }
+#endif
   // TODO(beng): move more of NWW::OnCreate here.
   return 0;
 }
@@ -2042,6 +2075,23 @@
   // ResetWindowRegion is going to trigger WM_NCPAINT. By doing it after we've
   // invoked OnSize we ensure the RootView has been laid out.
   ResetWindowRegion(false, true);
+
+#if defined(USE_AURA)
+  // As documented in the HWNDMessageHandler::OnCreate function, we add the
+  // WS_VSCROLL and WS_HSCROLL styles to the window to ensure that legacy track
+  // pad/trackpoint drivers generate the WM_VSCROLL and WM_HSCROLL messages.
+  // We want the style to be present on the window. However we don't want
+  // Windows to draw the scrollbars. To achieve this we hide the scroll bars

[sky, 2014/01/10 16:43:21]

Could we instead set the scrollbar sizes to 0?

[ananta, 2014/01/10 18:59:21]

Tricky to do that. The non AURA code did this in the WebContentsViewWin class
which parented the RenderWidgetHostViewWin window. It returned 0 in its
nccalcsize handler to set the scrollbar size to 0. Tricky to do that in AURA
given that we have one window and this would require mucking with the nccalcsize
rects.

+  // and readd them to the window style in a posted task which works.
+  if (IsTopLevelWindow(hwnd())) {
+    BOOL visible = ::IsWindowVisible(hwnd());
+    ShowScrollBar(hwnd(), SB_BOTH, FALSE);
+    long current_style = ::GetWindowLong(hwnd(), GWL_STYLE);
+    base::MessageLoop::current()->PostTask(
+        FROM_HERE,
+        base::Bind(&AddScrollStylesToWindow, hwnd()));
+#endif
+  }
 }
 
 void HWNDMessageHandler::OnSysCommand(UINT notification_code,
@@ -2255,6 +2305,15 @@
   SetMsgHandled(FALSE);
 }
 
+LRESULT HWNDMessageHandler::OnScrollMessage(UINT message,
+                                            WPARAM w_param,
+                                            LPARAM l_param) {
+  MSG msg = { hwnd(), message, w_param, l_param, GetMessageTime() };
+  ui::ScrollEvent event(msg);
+  delegate_->HandleScrollEvent(event);
+  return 0;
+}
+
 void HWNDMessageHandler::HandleTouchEvents(const TouchEvents& touch_events) {
   base::WeakPtr<HWNDMessageHandler> ref(weak_factory_.GetWeakPtr());
   for (size_t i = 0; i < touch_events.size() && ref; ++i)