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) {

[sky, 2014/01/10 19:18:42]

Is this still needed? Can't you key off the styles at the time you create the
window and set some boolean?

[ananta, 2014/01/10 20:05:36]

Removed. Added a member flag

+  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
@@ -1965,6 +1983,15 @@
   return 0;
 }
 
+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;
+}
+
 LRESULT HWNDMessageHandler::OnSetCursor(UINT message,
                                         WPARAM w_param,
                                         LPARAM l_param) {
@@ -2042,6 +2069,23 @@
   // 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)
+  // We add the WS_VSCROLL and WS_HSCROLL styles to top level windows to ensure
+  // that legacy trackpad/trackpoint drivers generate the WM_VSCROLL and
+  // WM_HSCROLL messages and scrolling works.
+  // 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())) {
+    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,