Adding a gray semi transparent backdrop behind the topmost window within the default container

ash/wm/maximize_mode/workspace_backdrop_delegate.cc

Index: ash/wm/maximize_mode/workspace_backdrop_delegate.cc
diff --git a/ash/wm/maximize_mode/workspace_backdrop_delegate.cc b/ash/wm/maximize_mode/workspace_backdrop_delegate.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b03ea253892f69081aa2686e97389e2276f57022
--- /dev/null
+++ b/ash/wm/maximize_mode/workspace_backdrop_delegate.cc
@@ -0,0 +1,128 @@
+// Copyright (c) 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 "ash/wm/maximize_mode/workspace_backdrop_delegate.h"
+
+#include "ash/wm/window_animations.h"
+#include "ui/aura/window.h"
+#include "ui/compositor/layer.h"
+#include "ui/compositor/scoped_layer_animation_settings.h"
+#include "ui/views/background.h"
+#include "ui/views/corewm/window_util.h"
+#include "ui/views/widget/widget.h"
+
+namespace ash {
+
+namespace internal {
+
+namespace {
+
+// The opacity of the backdrop.
+const float kBackdropOpacity = 0.5f;
+
+}  // namespace
+
+WorkspaceBackdropDelegate::WorkspaceBackdropDelegate(aura::Window* container)
+    : background_(NULL),
+      container_(container),
+      inside_(false) {
+  background_ = new views::Widget;

[sky, 2014/03/06 21:34:13]

Is there a reason why you don't use a layer directly?

[Mr4D (OOO till 08-26), 2014/03/07 01:00:12]

Yes, swallowing events.

+  views::Widget::InitParams params(views::Widget::InitParams::TYPE_CONTROL);
+  params.parent = container_;
+  params.bounds = container_->bounds();
+  // To disallow the MRU list from picking this window up it should not be
+  // activateable.
+  params.can_activate = false;
+  background_->Init(params);
+  background_->GetNativeView()->SetName("WorkspaceBackdropDelegate");
+  views::View* contents_view = new views::View();
+  contents_view->set_background(

[sky, 2014/03/06 21:34:13]

I'm skeptical you need a widget here, but if you do can't you accomplish this
with a colored layer?

[Mr4D (OOO till 08-26), 2014/03/07 01:00:12]

Done.

+      views::Background::CreateSolidBackground(SK_ColorBLACK));
+  contents_view->SetEnabled(true);
+  background_->SetContentsView(contents_view);
+  Show();
+  RestackBackdrop();
+  container_->AddObserver(this);
+}
+
+WorkspaceBackdropDelegate::~WorkspaceBackdropDelegate() {
+  container_->RemoveObserver(this);
+  ui::ScopedLayerAnimationSettings settings(
+      background_->GetNativeView()->layer()->GetAnimator());
+  background_->Close();
+  settings.AddObserver(views::corewm::CreateHidingWindowAnimationObserver(
+      background_->GetNativeView()));
+  background_->GetNativeView()->layer()->SetOpacity(0.0f);
+}
+
+void WorkspaceBackdropDelegate::RestackBackdrop() {
+  // Avoid recursive calls.
+  if (inside_)
+    return;
+  // We are stuffing the backdrop behind the first visible & qualifying
+  // window in the given container.
+  const aura::Window::Windows& windows = container_->children();
+  for (aura::Window::Windows::const_reverse_iterator window_iter =

[sky, 2014/03/06 21:34:13]

nit: I think this would be easier to follow if you had a function that returned
the window to stack behind and then the restacking logic.

[Mr4D (OOO till 08-26), 2014/03/07 01:00:12]

Done.

+           windows.rbegin();
+       window_iter != windows.rend(); ++window_iter) {
+    aura::Window* window = *window_iter;
+    if (window->IsVisible() &&
+        window->type() == ui::wm::WINDOW_TYPE_NORMAL) {

[sky, 2014/03/06 21:34:13]

If window has a transient parent in the same container should the backdrop be
behind the transient parent?

[Mr4D (OOO till 08-26), 2014/03/07 01:00:12]

As long as the transient window can get Alt+Tabbed not.

+      // Check if the window has already the backdrop directly behind it.
+      if (++window_iter != windows.rend()) {
+        if (*window_iter == background_->GetNativeWindow() &&
+            background_->IsVisible()) {
+          return;
+        }
+      }
+      // We are changing the order of windows which will cause recursion.
+      inside_ = true;

[sky, 2014/03/06 21:34:13]

Use autoreset. Please rename inside_ to better match what's happening. Maybe
in_restacking_ or something.

[Mr4D (OOO till 08-26), 2014/03/07 01:00:12]

Done.

+      if (!background_->IsVisible())
+        Show();
+      // Since the backdrop needs to be immediately behind the window and the
+      // stacking functions only guarantee a "it's above or below", we need
+      // to re-arrange the two windows twice.
+      container_->StackChildAbove(background_->GetNativeView(), window);
+      container_->StackChildAbove(window, background_->GetNativeView());
+      inside_ = false;
+      return;
+    }
+  }
+  // Hide backdrop since no suitable window was found.
+  if (background_->IsVisible())
+    background_->Hide();
+}
+
+void WorkspaceBackdropDelegate::OnWindowBoundsChanged(aura::Window* window,
+                                   const gfx::Rect& old_bounds,
+                                   const gfx::Rect& new_bounds) OVERRIDE {
+  // The container size has changed and the layer needs to be adapt to it.
+  AdjustToContainerBounds();
+}
+
+void WorkspaceBackdropDelegate::AdjustToContainerBounds() {
+  // Cover the entire container window.
+  gfx::Rect target_rect(gfx::Point(0, 0), container_->bounds().size());
+  if (target_rect != background_->GetNativeWindow()->bounds()) {
+    // This needs to be instantly.
+    ui::ScopedLayerAnimationSettings settings(
+        background_->GetNativeView()->layer()->GetAnimator());
+    settings.SetTransitionDuration(base::TimeDelta::FromMilliseconds(0));
+    background_->GetNativeWindow()->SetBounds(target_rect);
+    if (!background_->IsVisible())
+      background_->GetNativeView()->layer()->SetOpacity(kBackdropOpacity);
+  }
+}
+
+void WorkspaceBackdropDelegate::Show() {
+  background_->GetNativeView()->layer()->SetOpacity(0.0f);
+  background_->Show();
+  ui::ScopedLayerAnimationSettings settings(
+      background_->GetNativeView()->layer()->GetAnimator());
+  background_->Show();
+  background_->GetNativeView()->layer()->SetOpacity(kBackdropOpacity);
+}
+
+}  // namespace internal
+}  // namespace ash