Fix panel dragging on Linux Aura

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 #include <X11/extensions/shape.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xatom.h>
 #include <X11/Xregion.h>
@@ skipping 926 matching lines @@
       swa.override_redirect = True;
       window_type = atom_cache_.GetAtom("_NET_WM_WINDOW_TYPE_DND");
       break;
     default:
       window_type = atom_cache_.GetAtom("_NET_WM_WINDOW_TYPE_NORMAL");
       break;
   }
   if (swa.override_redirect)
     attribute_mask |= CWOverrideRedirect;
 
+  x_bounds_ = params.bounds;
   bounds_ = params.bounds;
   xwindow_ = XCreateWindow(
       xdisplay_, x_root_window_,
       bounds_.x(), bounds_.y(),
       bounds_.width(), bounds_.height(),
       0,               // border width
       CopyFromParent,  // depth
       InputOutput,
       CopyFromParent,  // visual
       attribute_mask,
@@ skipping 156 matching lines @@
 }
 
 void DesktopWindowTreeHostX11::OnCaptureReleased() {
   x11_capture_.reset();
   g_current_capture = NULL;
   OnHostLostWindowCapture();
   native_widget_delegate_->OnMouseCaptureLost();
 }
 
 void DesktopWindowTreeHostX11::DispatchMouseEvent(ui::MouseEvent* event) {
+  // The event location is relative to |x_bounds_|. However, Aura uses |bounds_|
+  // for all computations, including converting to screen coordinates. Offset
+  // the event location so that converting the event location to screen
+  // coordinates returns the correct value.
+  gfx::Vector2d event_offset(x_bounds_.origin() - bounds_.origin());
+  event->set_location(event->location() + event_offset);
+  event->set_root_location(event->location() + event_offset);
+

[sadrul, 2014/03/13 15:41:31]

This doesn't look right. Can you update
DesktopWindowTreeHostX11::GetClientAreaBoundsInScreen() instead to return
x_bounds_?

[pkotwicz, 2014/03/13 19:47:48]

I think I understand what you are asking.
You are hoping that we will be able to return a correct position in the event
window and a correct position in screen coordinates.

Personally I prefer my solution over yours.

A couple comments about your solution:
- We really should not be highjacking
DesktopWindowTreeHostX11::GetClientAreaBoundsInScreen() to return the real
window bounds. Retrieving |x_bounds_| is not the same as calling GetClientRect()
http://msdn.microsoft.com/en-us/library/aa932115.aspx
- |x_bounds_| should only have the real origin of the window (not its real
size). I foresee a plethora of theoretical problems with the local size being
different from the size in screen coordinates.

I think that it is ok for the position of the mouse event in the coordinates of
the event window to be off while the window is being moved. Do you foresee any
problems with this being the case?

   if (!g_current_capture || g_current_capture == this) {
     SendEventToProcessor(event);
   } else {
     // Another DesktopWindowTreeHostX11 has installed itself as
     // capture. Translate the event's location and dispatch to the other.
     event->ConvertLocationToTarget(window(), g_current_capture->window());
     g_current_capture->SendEventToProcessor(event);
   }
 }
 
@@ skipping 192 matching lines @@
       DCHECK_EQ(xwindow_, xev->xconfigure.window);
       DCHECK_EQ(xwindow_, xev->xconfigure.event);
       // It's possible that the X window may be resized by some other means than
       // from within aura (e.g. the X window manager can change the size). Make
       // sure the root window size is maintained properly.
       int translated_x = xev->xconfigure.x;
       int translated_y = xev->xconfigure.y;
       if (!xev->xconfigure.send_event && !xev->xconfigure.override_redirect) {
         Window unused;
         XTranslateCoordinates(xdisplay_, xwindow_, x_root_window_,
             0, 0, &translated_x, &translated_y, &unused);

[pkotwicz, 2014/03/13 03:49:45]

The event coordinates matched exactly those that I got from the x_root and
y_root properties of the MotionNotify event if I skipped calling
XTranslateCoordinates().
Do you know why this would be the case?

[sadrul, 2014/03/13 15:41:31]

I don't understand what you are asking. This is handling a ConfigureNotify
event, not MotionNotify. (see https://codereview.chromium.org/12319091 for
XTranslateCoordinates)

[pkotwicz, 2014/03/13 19:47:48]

Sorry for not being clear. I understand why XTranslateCoordinates() is
desireable.

I implemented a different technique to correct the mouse event location in
DesktopWindowTreeHostX11::DispatchMouseEvent() by using x_root and y_root in
MotionNotify. (root_x and root_y in XI_Motion)
By removing the call to XTranslateCoordinates() here, the mouse position
computed in DispatchMouseEvent() using that technique and with this CL (minus
XTranslateCoordinates) returns the same value.

       }
       gfx::Rect bounds(translated_x, translated_y,
                        xev->xconfigure.width, xev->xconfigure.height);
       bool size_changed = bounds_.size() != bounds.size();
       bool origin_changed = bounds_.origin() != bounds.origin();
       previous_bounds_ = bounds_;
+      x_bounds_ = bounds;
       bounds_ = bounds;
       if (size_changed)
         OnHostResized(bounds.size());
       if (origin_changed)
         OnHostMoved(bounds_.origin());
       ResetWindowRegion();
       break;
     }
     case GenericEvent: {
       ui::TouchFactory* factory = ui::TouchFactory::GetInstance();
@@ skipping 212 matching lines @@
   if (linux_ui) {
     ui::NativeTheme* native_theme = linux_ui->GetNativeTheme();
     if (native_theme)
       return native_theme;
   }
 
   return ui::NativeTheme::instance();
 }
 
 }  // namespace views