Realign message center popups when displays are added or removed

ui/message_center/views/desktop_popup_alignment_delegate.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/message_center/views/desktop_popup_alignment_delegate.h"
 
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/message_center/message_center_style.h"
 #include "ui/message_center/views/message_popup_collection.h"
 
 namespace message_center {
 
 DesktopPopupAlignmentDelegate::DesktopPopupAlignmentDelegate()
     : alignment_(POPUP_ALIGNMENT_BOTTOM | POPUP_ALIGNMENT_RIGHT),
-      display_id_(display::Display::kInvalidDisplayID),
+      primary_display_id_(display::Display::kInvalidDisplayID),
       screen_(NULL) {}
 
 DesktopPopupAlignmentDelegate::~DesktopPopupAlignmentDelegate() {
   if (screen_)
     screen_->RemoveObserver(this);
 }
 
 void DesktopPopupAlignmentDelegate::StartObserving(display::Screen* screen) {
   if (screen_ || !screen)
     return;
 
   screen_ = screen;
   screen_->AddObserver(this);
   display::Display display = screen_->GetPrimaryDisplay();
-  display_id_ = display.id();
+  primary_display_id_ = display.id();
   RecomputeAlignment(display);
 }
 
 int DesktopPopupAlignmentDelegate::GetToastOriginX(
     const gfx::Rect& toast_bounds) const {
   if (IsFromLeft())
     return work_area_.x() + kMarginBetweenItems;
   return work_area_.right() - kMarginBetweenItems - toast_bounds.width();
 }
 
@@ skipping 33 matching lines @@
   // the taskbar is on the top or bottom.
   // Since on some platforms like Ubuntu Unity there's also a launcher along
   // with a taskbar (panel), we need to check that there is really nothing at
   // the top before concluding that the taskbar is at the left.
   alignment_ |= (work_area_.x() > display.bounds().x() &&
                  work_area_.y() == display.bounds().y())
       ? POPUP_ALIGNMENT_LEFT
       : POPUP_ALIGNMENT_RIGHT;
 }
 
+// Anytime the display configuration changes, we need to recompute the alignment
+// on the primary display.
+void DesktopPopupAlignmentDelegate::UpdatePrimaryDisplay() {
+  display::Display primary_display = screen_->GetPrimaryDisplay();
+  if (primary_display.id() != primary_display_id_) {
+    primary_display_id_ = primary_display.id();
+    RecomputeAlignment(primary_display);
+    DoUpdateIfPossible();
+  }
+}
+
 void DesktopPopupAlignmentDelegate::OnDisplayAdded(
-    const display::Display& new_display) {}
+    const display::Display& added_display) {
+  // The added display could be the new primary display.
+  UpdatePrimaryDisplay();
+}
 
 void DesktopPopupAlignmentDelegate::OnDisplayRemoved(
-    const display::Display& old_display) {}
+    const display::Display& removed_display) {
+  // The removed display may have been the primary display.
+  UpdatePrimaryDisplay();
+}
 
 void DesktopPopupAlignmentDelegate::OnDisplayMetricsChanged(
     const display::Display& display,
     uint32_t metrics) {
-  if (display.id() == display_id_) {
-    RecomputeAlignment(display);
-    DoUpdateIfPossible();
-  }
+  // Set to kInvalidDisplayID so the alignment is updated regardless of whether

[dewittj, 2016/06/27 17:37:27]

Why always recompute the alignment?

[osandov, 2016/06/27 19:22:52]

I wanted to reuse the helper to handle all of the cases. We need the recompute
if the primary display changes resolution or switches to another display. If
another display resizes, we do some unnecessary work, but this seemed like the
cleanest way to implement it.

+  // the primary display actually changed.
+  primary_display_id_ = display::Display::kInvalidDisplayID;
+  UpdatePrimaryDisplay();
 }
 
 }  // namespace message_center