Reorder the NativeViews attached to a view via kViewHostKey according to the position of the view

ui/views/widget/native_widget_layer_reorderer_aura.cc

+// Copyright (c) 2013 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/native_widget_layer_reorderer_aura.h"
+
+#include <map>
+#include <vector>
+
+#include "ui/aura/window.h"
+#include "ui/views/view.h"
+#include "ui/views/view_constants_aura.h"
+
+namespace views {
+
+namespace {
+
+// Sets |hosted_windows| to a mapping of the views with an attached window to
+// the window that they are attached to. Only views attached to a child of
+// |parent_window| are returned.
+void GetViewsWithAttachedWindow(
+    const aura::Window& parent_window,
+    std::map<views::View*, aura::Window*>* hosted_windows) {
+  const std::vector<aura::Window*>& child_windows = parent_window.children();
+  for (size_t i = 0; i < child_windows.size(); ++i) {
+    aura::Window* child = child_windows[i];
+    View* host_view = child->GetProperty(kHostViewKey);
+    if (host_view)
+      (*hosted_windows)[host_view] = child;
+  }
+}
+
+// Sets |order| to the list of views whose layer / attached window's layer
+// is a child of |parent_layer|. |order| is sorted in ascending z-order of
+// the views.
+// |hosts| are the views with an attached window whose layer is a child of
+// |parent_layer|.
+void GetOrderOfViewsWithLayers(
+    views::View* view,
+    ui::Layer* parent_layer,
+    const std::map<views::View*, aura::Window*>& hosts,
+    std::vector<views::View*>* order) {
+  DCHECK(view);
+  DCHECK(parent_layer);
+  DCHECK(order);
+  if (view->layer() && view->layer()->parent() == parent_layer) {
+    order->push_back(view);
+    // |hosts| may contain a child of |view|.
+  } else if (hosts.find(view) != hosts.end()) {
+    order->push_back(view);
+  }
+
+  for (int i = 0; i < view->child_count(); ++i)
+    GetOrderOfViewsWithLayers(view->child_at(i), parent_layer, hosts, order);
+}
+
+}  // namespace
+
+NativeWidgetLayerReordererAura::NativeWidgetLayerReordererAura(
+    aura::Window* window,
+    View* root_view)
+    : window_(window),
+      root_view_(root_view) {
+  window_->AddObserver(this);
+  const std::vector<aura::Window*>& child_windows = window_->children();
+  for (size_t i = 0; i < child_windows.size(); ++i)
+    child_windows[i]->AddObserver(this);
+}
+
+NativeWidgetLayerReordererAura::~NativeWidgetLayerReordererAura() {
+  if (window_)
+    StopObserving(window_);
+}
+
+void NativeWidgetLayerReordererAura::ReorderChildWindowLayers() {
+  DCHECK(window_);
+
+  std::map<View*, aura::Window*> hosted_windows;
+  GetViewsWithAttachedWindow(*window_, &hosted_windows);
+
+  if (hosted_windows.empty()) {
+    // Exit early if there are no views with attached windows.
+    // View::ReorderLayers() should have already reordered the layers owned by
+    // views.
+    return;
+  }
+
+  // Compute the desired z-order of the layers based on the order of the views
+  // with layers and views with attached windows in the view tree.
+  std::vector<View*> view_with_layer_order;
+  GetOrderOfViewsWithLayers(root_view_, window_->layer(), hosted_windows,
+      &view_with_layer_order);
+
+  // Reorder the layers and windows.
+  for (std::vector<View*>::reverse_iterator it = view_with_layer_order.rbegin();
+       it != view_with_layer_order.rend(); ++it) {
+    View* view = *it;
+    ui::Layer* layer = view->layer();
+    aura::Window* window = NULL;
+
+    std::map<View*, aura::Window*>::iterator hosted_window_it =
+        hosted_windows.find(view);
+    if (hosted_window_it != hosted_windows.end()) {
+      window = hosted_window_it->second;
+      layer = window->layer();
+    }
+
+    DCHECK(layer);
+    if (window)
+      window_->StackChildAtBottom(window);
+    window_->layer()->StackAtBottom(layer);

[sky, 2013/05/24 15:57:26]

Don't we only care about items in hosted_windows here?

[pkotwicz, 2013/05/26 04:12:15]

IMHO, it's simpler (and safer) to reorder both layers owned by views and layers
associated to a view. I added a comment documenting this.

+  }
+}
+
+void NativeWidgetLayerReordererAura::StopObserving(aura::Window* window) {
+  window->RemoveObserver(this);

[sky, 2013/05/24 15:57:26]

It's subtle and easy to get wrong that you're observing both window_ and all its
children. Please document this some where. In fact consider forking off a
separate class just to handle the property change case, which should make the
code less error prone.

[pkotwicz, 2013/05/26 04:12:15]

Added a separate class

+  if (window_ == window){
+    const std::vector<aura::Window*>& child_windows = window_->children();
+    for (size_t i = 0; i < child_windows.size(); ++i)
+      child_windows[i]->RemoveObserver(this);
+    window_ = NULL;
+  }
+}
+
+void NativeWidgetLayerReordererAura::OnWindowAdded(aura::Window* new_window) {
+  if (new_window->parent() == window_) {
+    new_window->AddObserver(this);
+    ReorderChildWindowLayers();
+  }
+}
+
+void NativeWidgetLayerReordererAura::OnWillRemoveWindow(aura::Window* window) {
+  if (window->parent() == window_)

[sky, 2013/05/24 15:57:26]

Why do you care about this case?

[pkotwicz, 2013/05/26 04:12:15]

This is no longer relevant because I separated the window observer for |window_|
and the window observer for |window_|'s children into a seperate class

+    StopObserving(window);
+}
+
+void NativeWidgetLayerReordererAura::OnWindowPropertyChanged(
+    aura::Window* window,
+    const void* key,
+    intptr_t old) {
+  if (key == kHostViewKey && window != window_)
+    ReorderChildWindowLayers();
+}
+
+void NativeWidgetLayerReordererAura::OnWindowDestroying(aura::Window* window) {
+  StopObserving(window);
+}
+
+}  // namespace views