exo: Fix cursor size for multi-display ARC

components/exo/pointer.cc

 // Copyright 2015 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 "components/exo/pointer.h"
 
 #include "ash/public/cpp/shell_window_ids.h"
 #include "components/exo/pointer_delegate.h"
 #include "components/exo/pointer_stylus_delegate.h"
 #include "components/exo/surface.h"
@@ skipping 289 matching lines @@
   if (!target)
     return nullptr;
 
   return delegate_->CanAcceptPointerEventsForSurface(target) ? target : nullptr;
 }
 
 void Pointer::UpdateCursorScale() {
   if (!focus_)
     return;
 
+  auto screen = display::Screen::GetScreen();
+  auto helper = WMHelper::GetInstance();
+
   // Update cursor scale if the effective UI scale has changed.
-  display::Display display =
-      display::Screen::GetScreen()->GetDisplayNearestWindow(
-          widget_->GetNativeWindow());
-  float ui_scale = WMHelper::GetInstance()
-                       ->GetDisplayInfo(display.id())
-                       .GetEffectiveUIScale();
-  if (WMHelper::GetInstance()->GetCursorSet() == ui::CURSOR_SET_LARGE)
+  auto display = screen->GetDisplayNearestWindow(widget_->GetNativeWindow());

[reveman, 2017/01/23 22:22:34]

nit: Avoid "auto" here to make it clear what the type of "display" is

fyi, I prefer to avoid "auto" unless when we're duplicating type names (e.g.
"auto a = new Type" is ok) or it's making the code significantly more easy to
read (often the case for iterators)

[Dominik Laskowski, 2017/01/23 23:50:53]

Done, and above too.

+  float ui_scale = helper->GetDisplayInfo(display.id()).GetEffectiveUIScale();
+

[reveman, 2017/01/23 22:22:34]

nit: is this blank line intentional? remove if not

[Dominik Laskowski, 2017/01/23 23:50:53]

Removed in second patch.

+  float primary_dsf = screen->GetPrimaryDisplay().device_scale_factor();

[reveman, 2017/01/23 22:22:34]

nit: remove abbreviation. s/primary_dsf/primary_device_scale_factor/

[Dominik Laskowski, 2017/01/23 23:50:53]

Done.

+
+  // The cursor is scaled down by the DSF of the primary display, and its

[reveman, 2017/01/23 22:22:34]

scaled up?

[Dominik Laskowski, 2017/01/23 23:50:53]

I meant that the surface size is divided by the primary DSF. Changed the
wording.

+  // physical size is proportional to the DSF of the internal display. For
+  // external displays (and the internal display when secondary to a display
+  // with a different DSF), scale the cursor so its physical size matches with
+  // the single display case.
+  if (!display.IsInternal() || display.device_scale_factor() != primary_dsf) {
+    auto info = helper->GetDisplayInfo(display::Display::InternalDisplayId());

[reveman, 2017/01/23 22:22:34]

nit: maybe internal_display_device_scale_factor instead or skip the variable
completely?

[Dominik Laskowski, 2017/01/23 23:50:53]

Removed variable.

+    ui_scale *= primary_dsf / info.device_scale_factor();
+  }
+
+  if (helper->GetCursorSet() == ui::CURSOR_SET_LARGE)
     ui_scale *= kLargeCursorScale;
 
   if (ui_scale != cursor_scale_) {
     gfx::Transform transform;
     transform.Scale(ui_scale, ui_scale);
     widget_->GetNativeWindow()->SetTransform(transform);
     cursor_scale_ = ui_scale;
   }
 }
 
 }  // namespace exo