Fix tab drag and drop with hi-dpi.

ui/views/widget/desktop_aura/x11_topmost_window_finder.cc

 // Copyright 2014 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/x11_topmost_window_finder.h"
 
 #include <X11/Xutil.h>
 
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/window.h"
+#include "ui/gfx/screen.h"
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 namespace views {
 
+float GetDeviceScaleFactor() {
+  gfx::Display display = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay();
+  return display.device_scale_factor();
+}
+
+gfx::Point DIPToPixelPoint(const gfx::Point& dip_point) {
+  return ToFlooredPoint(gfx::ScalePoint(dip_point, GetDeviceScaleFactor()));
+}
+
 X11TopmostWindowFinder::X11TopmostWindowFinder() : toplevel_(None) {
 }
 
 X11TopmostWindowFinder::~X11TopmostWindowFinder() {
 }
 
 aura::Window* X11TopmostWindowFinder::FindLocalProcessWindowAt(
     const gfx::Point& screen_loc,
     const std::set<aura::Window*>& ignore) {
-  screen_loc_ = screen_loc;
+  screen_loc_ = DIPToPixelPoint(screen_loc);

[sadrul, 2015/03/19 23:46:58]

Since FindWindowAt() takes screen_loc in physical-pixel space, I think it would
be better to have FindLocalProcessWindowAt() also take screen_loc in
physical-pixels. Please make sure to append |in_pixels| to the variable names to
clarify this.

[stapelberg, 2015/03/20 08:34:40]

Done.

   ignore_ = ignore;
 
   std::vector<aura::Window*> local_process_windows =
       DesktopWindowTreeHostX11::GetAllOpenWindows();
   bool found_local_process_window = false;
   for (size_t i = 0; i < local_process_windows.size(); ++i) {
     if (ShouldStopIteratingAtLocalProcessWindow(local_process_windows[i])) {
       found_local_process_window = true;
       break;
     }
@@ skipping 48 matching lines @@
   if (!host->GetX11RootWindowOuterBounds().Contains(screen_loc_))
     return false;
 
   ::Region shape = host->GetWindowShape();
   if (!shape)
     return true;
 
   aura::client::ScreenPositionClient* screen_position_client =
       aura::client::GetScreenPositionClient(window->GetRootWindow());
   gfx::Point window_loc(screen_loc_);
   screen_position_client->ConvertPointFromScreen(window, &window_loc);

[sadrul, 2015/03/19 23:47:40]

Oh, also, does this do the right thing?  (I seem to remember the
ScreenPositionClient actually working in DIP)

[stapelberg, 2015/03/20 08:34:40]

I’m not sure — the code path never gets executed for me. How can I make chromium
use a non-rectangular window shape at all?

[sadrul, 2015/03/20 17:40:23]

Ah, you need some chrome app that sets custom windows (I think hangouts, keep
apps do).

It would be OK if you want to address this separately from this patch.

[stapelberg, 2015/03/20 21:48:06]

I see. I’d like to postpone this until later, and focus on getting the 99%
use-case in first :).

   return XPointInRegion(shape, window_loc.x(), window_loc.y()) == True;
 }
 
 }  // namespace views