Ash window cycle ui: don't create mirrored layers for previews until

ash/wm/window_mirror_view.cc

 // Copyright 2016 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/window_mirror_view.h"
 
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/wm/forwarding_layer_delegate.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/wm/window_state_aura.h"
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_tree_owner.h"
+#include "ui/views/widget/widget.h"
 
 namespace ash {
 namespace wm {
 namespace {
 
 void EnsureAllChildrenAreVisible(ui::Layer* layer) {
   std::list<ui::Layer*> layers;
   layers.push_back(layer);
   while (!layers.empty()) {
     for (auto* child : layers.front()->children())
       layers.push_back(child);
     layers.front()->SetVisible(true);
     layers.pop_front();
   }
 }
 
 }  // namespace
 
 WindowMirrorView::WindowMirrorView(WmWindowAura* window) : target_(window) {
   DCHECK(window);
 }
 WindowMirrorView::~WindowMirrorView() {}
 
-void WindowMirrorView::Init() {
-  SetPaintToLayer(true);
-
-  layer_owner_ = ::wm::RecreateLayers(target_->aura_window(), this);
-
-  GetMirrorLayer()->parent()->Remove(GetMirrorLayer());
-  layer()->Add(GetMirrorLayer());
-
-  // Some extra work is needed when the target window is minimized.
-  if (target_->GetWindowState()->IsMinimized()) {
-    GetMirrorLayer()->SetVisible(true);
-    GetMirrorLayer()->SetOpacity(1);
-    EnsureAllChildrenAreVisible(GetMirrorLayer());
-  }
-}
-
 gfx::Size WindowMirrorView::GetPreferredSize() const {
   return target_->GetBounds().size();
 }
 
 void WindowMirrorView::Layout() {
+  // If |layer_owner_| hasn't been initialized (|this| isn't on screen), no-op.
+  if (!layer_owner_)
+    return;
+
   // Position at 0, 0.
   GetMirrorLayer()->SetBounds(gfx::Rect(GetMirrorLayer()->bounds().size()));
 
   // Scale down if necessary.
   gfx::Transform mirror_transform;
   if (size() != target_->GetBounds().size()) {
     const float scale =
         width() / static_cast<float>(target_->GetBounds().width());
     mirror_transform.Scale(scale, scale);
   }
   GetMirrorLayer()->SetTransform(mirror_transform);
 }
 
+bool WindowMirrorView::GetNeedsNotificationWhenVisibleBoundsChange() const {
+  return true;
+}
+
+void WindowMirrorView::OnVisibleBoundsChanged() {
+  if (!layer_owner_ && !GetVisibleBounds().IsEmpty())
+    InitLayerOwner();
+}
+
 ui::LayerDelegate* WindowMirrorView::CreateDelegate(
     ui::LayerDelegate* delegate) {
   if (!delegate)
     return nullptr;
   delegates_.push_back(
       base::WrapUnique(new ForwardingLayerDelegate(target_, delegate)));
 
   return delegates_.back().get();
 }
 
+void WindowMirrorView::InitLayerOwner() {
+  SetPaintToLayer(true);
+
+  layer_owner_ = ::wm::RecreateLayers(target_->aura_window(), this);
+
+  GetMirrorLayer()->parent()->Remove(GetMirrorLayer());
+  layer()->Add(GetMirrorLayer());
+
+  // Some extra work is needed when the target window is minimized.
+  if (target_->GetWindowState()->IsMinimized()) {
+    GetMirrorLayer()->SetVisible(true);
+    GetMirrorLayer()->SetOpacity(1);
+    EnsureAllChildrenAreVisible(GetMirrorLayer());
+  }
+
+  Layout();
+}
+
 ui::Layer* WindowMirrorView::GetMirrorLayer() {
   return layer_owner_->root();
 }
 
 }  // namespace wm
 }  // namespace ash