Use XGrabPointer instead of XChangeActivatePointerGrab() to change the cursor during a pointer grab

ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc

Index: ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
diff --git a/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc b/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
index 8c20313bf87401e6513e9d30177b3adbb7699d3e..7cc104eff28904312051a0dcf2f3001b2a9ccd5f 100644
--- a/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
+++ b/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
@@ -39,7 +39,6 @@ const unsigned int kModifiersMasks[] = {
 X11WholeScreenMoveLoop::X11WholeScreenMoveLoop(X11MoveLoopDelegate* delegate)
     : delegate_(delegate),
       in_move_loop_(false),
-      initial_cursor_(ui::kCursorNull),
       should_reset_mouse_flags_(false),
       grab_input_window_(None),
       grabbed_pointer_(false),
@@ -122,14 +121,9 @@ uint32_t X11WholeScreenMoveLoop::DispatchEvent(const ui::PlatformEvent& event) {
   return ui::POST_DISPATCH_PERFORM_DEFAULT;
 }
 
-bool X11WholeScreenMoveLoop::RunMoveLoop(aura::Window* source,
-                                         gfx::NativeCursor cursor) {
+bool X11WholeScreenMoveLoop::RunMoveLoop(aura::Window* source) {
   DCHECK(!in_move_loop_);  // Can only handle one nested loop at a time.
 
-  // Query the mouse cursor prior to the move loop starting so that it can be
-  // restored when the move loop finishes.
-  initial_cursor_ = source->GetHost()->last_cursor();
-
   grab_input_window_ = CreateDragInputWindow(gfx::GetXDisplay());
 
   // Only grab mouse capture of |grab_input_window_| if |source| does not have
@@ -144,7 +138,7 @@ bool X11WholeScreenMoveLoop::RunMoveLoop(aura::Window* source,
     aura::client::CaptureClient* capture_client =
         aura::client::GetCaptureClient(source->GetRootWindow());
     CHECK(capture_client->GetGlobalCaptureWindow() == NULL);
-    grabbed_pointer_ = GrabPointer(cursor);
+    grabbed_pointer_ = GrabPointer();
     if (!grabbed_pointer_) {
       XDestroyWindow(gfx::GetXDisplay(), grab_input_window_);
       return false;
@@ -180,13 +174,12 @@ bool X11WholeScreenMoveLoop::RunMoveLoop(aura::Window* source,
 
 void X11WholeScreenMoveLoop::UpdateCursor(gfx::NativeCursor cursor) {
   if (in_move_loop_) {
-    // We cannot call GrabPointer() because we do not want to change the
-    // "owner_events" property of the active pointer grab.
-    XChangeActivePointerGrab(
-        gfx::GetXDisplay(),
-        ButtonPressMask | ButtonReleaseMask | PointerMotionMask,
-        cursor.platform(),
-        CurrentTime);
+    if (grabbed_pointer_) {
+      // Do not grab the server. We already have pointer grab.
+      ui::GrabPointer(grab_input_window_, false, cursor.platform());
+    } else {
+      NOTREACHED();
+    }
   }
 }
 
@@ -209,12 +202,10 @@ void X11WholeScreenMoveLoop::EndMoveLoop() {
   // the chrome process.
 
   // Ungrab before we let go of the window.
-  XDisplay* display = gfx::GetXDisplay();
   if (grabbed_pointer_)
-    XUngrabPointer(display, CurrentTime);
-  else
-    UpdateCursor(initial_cursor_);
+    ui::UngrabPointer();
 
+  XDisplay* display = gfx::GetXDisplay();
   unsigned int esc_keycode = XKeysymToKeycode(display, XK_Escape);
   for (size_t i = 0; i < arraysize(kModifiersMasks); ++i) {
     XUngrabKey(display, esc_keycode, kModifiersMasks[i], grab_input_window_);
@@ -230,22 +221,13 @@ void X11WholeScreenMoveLoop::EndMoveLoop() {
   quit_closure_.Run();
 }
 
-bool X11WholeScreenMoveLoop::GrabPointer(gfx::NativeCursor cursor) {
+bool X11WholeScreenMoveLoop::GrabPointer() {
   XDisplay* display = gfx::GetXDisplay();
   XGrabServer(display);
 
   // Pass "owner_events" as false so that X sends all mouse events to
   // |grab_input_window_|.
-  int ret = XGrabPointer(
-      display,
-      grab_input_window_,
-      False,  // owner_events
-      ButtonPressMask | ButtonReleaseMask | PointerMotionMask,
-      GrabModeAsync,
-      GrabModeAsync,
-      None,
-      cursor.platform(),
-      CurrentTime);
+  int ret = ui::GrabPointer(grab_input_window_, false, None);

[pkotwicz, 2014/12/22 23:44:16]

Passing None for the Cursor argument seems like the right thing to do.

According to http://tronche.com/gui/x/xlib/input/XGrabPointer.html
"If None is specified, the normal cursor for that window is displayed when the
pointer is in grab_window or one of its subwindows; otherwise, the cursor for
grab_window is displayed."

There is a bug where the mouse cursor unexpectedly changes to a text caret while
dragging a tab from one browser window to another. This CL does not make that
bug better or worse.

[sadrul, 2014/12/23 16:53:50]

This is different from what we do now though, right? So let's keep this change
(i.e. using None for Cursor) as a separate CL, so revert is easier if we need
to.

[pkotwicz, 2014/12/23 18:22:22]

I do not understand. If X11WholeScreenMoveLoop::RunMoveLoop() does not take a
cursor argument, which cursor should be passed in to GrabPointer()?
WindowTreeHost::last_cursor() is an option, but it will change the behavior of
Drag and Drop.
Previously, we were passing in the cursor passed in to RunMoveLoop() to
GrabPointer()

[sadrul, 2015/01/14 20:34:01]

Why not continue to do the same (i.e. why should we require two calls to
ui::GrabPointer() through a call to RunMoveLoop() and another call to
UpdateCursor())?

[pkotwicz, 2015/01/14 20:50:07]

The problem is that if RunMoveLoop() takes a cursor argument, then we need to
somehow revert to the old cursor when the move loop ends regardless of the value
of |grabbed_pointer_|.

In order to update the cursor of an XI2 grab, I would need to do a new grab and
know the value of owner_events in the original grab.

   if (ret != GrabSuccess) {
     DLOG(ERROR) << "Grabbing pointer for dragging failed: "
                 << ui::GetX11ErrorString(display, ret);