Don't track mouse events in HWNDMessageHandler when they are forwarded by the LegacyRenderWidgetHost

content/browser/renderer_host/legacy_render_widget_host_win.cc

Index: content/browser/renderer_host/legacy_render_widget_host_win.cc
===================================================================
--- content/browser/renderer_host/legacy_render_widget_host_win.cc	(revision 249762)
+++ content/browser/renderer_host/legacy_render_widget_host_win.cc	(working copy)
@@ -13,8 +13,19 @@
 #include "ui/base/touch/touch_enabled.h"
 #include "ui/gfx/geometry/rect.h"
 
+namespace {
+
+// This property is set on the parent window when we set capture on it. This
+// is used to retrieve the child window whose bounds we are tracking.
+const wchar_t kCaptureForcedOnParentByTrackingWindow[] =
+    L"CaptureForcedByTrackingWindow";
+
+}  // namespace
+
 namespace content {
 
+WNDPROC LegacyRenderWidgetHostHWND::g_parent_original_class_proc = NULL;
+
 LegacyRenderWidgetHostHWND::~LegacyRenderWidgetHostHWND() {
   ::DestroyWindow(hwnd());
 }
@@ -22,13 +33,15 @@
 // static
 scoped_ptr<LegacyRenderWidgetHostHWND> LegacyRenderWidgetHostHWND::Create(
     HWND parent) {
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kDisableLegacyIntermediateWindow))
+    return scoped_ptr<LegacyRenderWidgetHostHWND>();
+
   scoped_ptr<LegacyRenderWidgetHostHWND> legacy_window_instance;
   legacy_window_instance.reset(new LegacyRenderWidgetHostHWND(parent));
   // If we failed to create the child, or if the switch to disable the legacy
   // window is passed in, then return NULL.
-  if (!::IsWindow(legacy_window_instance->hwnd()) ||
-      CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kDisableLegacyIntermediateWindow))
+  if (!::IsWindow(legacy_window_instance->hwnd()))
     return scoped_ptr<LegacyRenderWidgetHostHWND>();
 
   legacy_window_instance->Init();
@@ -86,6 +99,21 @@
       ui::AreTouchEventsEnabled())
     RegisterTouchWindow(hwnd(), TWF_WANTPALM);
 
+  // We superclass the parent window class. This is to ensure that we avoid
+  // messy code tracking if the window was subclassed or not. Superclassing
+  // the parent ensures that we can windows subsequently created.
+  // Note: We never unsubclass. This should be safe.
+  if (!g_parent_original_class_proc) {

[sky, 2014/02/12 14:36:31]

Doesn't this assume the legacy hwnd always has a parent of the same class?

+    g_parent_original_class_proc = reinterpret_cast<WNDPROC>(
+        ::SetClassLong(GetParent(), GCL_WNDPROC,
+                       reinterpret_cast<long>(ParentWindowSuperClassProc)));
+    DCHECK(g_parent_original_class_proc);
+    // We need to subclass the first window as the super class does not take
+    // effect until a new window is created.
+    ::SetWindowLong(GetParent(), GWL_WNDPROC,
+                    reinterpret_cast<long>(ParentWindowSuperClassProc));
+  }
+
   HRESULT hr = ::CreateStdAccessibleObject(
       hwnd(), OBJID_WINDOW, IID_IAccessible,
       reinterpret_cast<void **>(window_accessible_.Receive()));
@@ -130,12 +158,21 @@
                                                  WPARAM w_param,
                                                  LPARAM l_param,
                                                  BOOL& handled) {
-  POINT mouse_coords;
-  mouse_coords.x = GET_X_LPARAM(l_param);
-  mouse_coords.y = GET_Y_LPARAM(l_param);
-  ::MapWindowPoints(hwnd(), GetParent(), &mouse_coords, 1);
-  return ::SendMessage(GetParent(), message, w_param,
-                       MAKELPARAM(mouse_coords.x, mouse_coords.y));
+  // We won't receive mouse messages when capture is with the parent window.
+  // If we receive a mouse move then it means that parent capture was released.
+  // This would happen if we lost focus or if the mouse left our window bounds
+  // and we released capture.
+  if (message == WM_MOUSEMOVE) {
+    if (::GetCapture() != GetParent()) {
+      ::SetCapture(GetParent());
+      ::SetProp(GetParent(), kCaptureForcedOnParentByTrackingWindow, hwnd());
+    }
+  } else if (message == WM_MOUSEWHEEL || message == WM_MOUSEHWHEEL) {
+    return ::SendMessage(GetParent(), message, w_param, l_param);
+  } else {
+    NOTREACHED() << "Unexpected mouse message received: " << message;
+  }
+  return 0;
 }
 
 LRESULT LegacyRenderWidgetHostHWND::OnMouseActivate(UINT message,
@@ -181,4 +218,42 @@
   return 0;
 }
 
+// static
+LRESULT CALLBACK LegacyRenderWidgetHostHWND::ParentWindowSuperClassProc(
+    HWND window, UINT message, WPARAM w_param, LPARAM l_param) {
+  // To ensure that the LegacyRenderWidgetHostHWND is as less intrusive as
+  // possible, we set capture on the parent window when we receive a
+  // mouse move message for the LegacyRenderWidgetHostHWND hwnd. This ensures
+  // that subsequent mouse messages go to the parent. We need to release this
+  // forced capture on the parent when the mouse cursor leaves the bounds of
+  // the LegacyRenderWidgetHostHWND window which is identified by the
+  // tracking_window local variable below. We only do this when no mouse
+  // buttons are down as in that case capture is released by code in the
+  // default parent mouse event handling.
+  const int mouse_down_flags =
+      MK_LBUTTON | MK_MBUTTON | MK_RBUTTON | MK_XBUTTON1 | MK_XBUTTON2;
+  if (message == WM_MOUSEMOVE && ::GetCapture() == window &&
+      !(w_param & mouse_down_flags)) {
+    HWND tracking_window = reinterpret_cast<HWND>(::GetProp(window,
+                                      kCaptureForcedOnParentByTrackingWindow));
+    if (::IsWindow(tracking_window)) {
+      POINT pt = {0};
+      pt.x = GET_X_LPARAM(l_param);
+      pt.y = GET_Y_LPARAM(l_param);
+      ::ClientToScreen(window, &pt);
+
+      RECT window_rect = {0};
+      ::GetWindowRect(tracking_window, &window_rect);
+      if (!::PtInRect(&window_rect, pt) ||
+          ::WindowFromPoint(pt) != tracking_window) {
+        ::ReleaseCapture();
+        ::RemoveProp(window, kCaptureForcedOnParentByTrackingWindow);
+      }
+    }
+  }
+  DCHECK(g_parent_original_class_proc);
+  return ::CallWindowProc(g_parent_original_class_proc, window, message,
+                          w_param, l_param);
+}
+
 }  // namespace content