CrOS Tablet Window management - Split Screen part I

ash/wm/splitview/split_view_controller.h

+// Copyright 2017 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.
+
+#ifndef ASH_WM_SPLITSVIEW_SPLIT_VIEW_CONTROLLER_H_
+#define ASH_WM_SPLITSVIEW_SPLIT_VIEW_CONTROLLER_H_
+
+#include "ash/ash_export.h"
+#include "ash/shell_observer.h"
+#include "ash/wm/window_state_observer.h"
+#include "base/macros.h"
+#include "base/observer_list.h"
+#include "ui/aura/window_observer.h"
+#include "ui/wm/public/activation_change_observer.h"
+
+namespace ash {
+
+class SplitViewControllerTest;
+
+// The controller for the split view. It snaps a window to left/right side of
+// the screen. It also observes the two snapped windows and decides when to exit
+// the split view mode.
+class ASH_EXPORT SplitViewController : public aura::WindowObserver,
+                                       public ash::wm::WindowStateObserver,
+                                       public ::wm::ActivationChangeObserver,
+                                       public ShellObserver {
+ public:
+  enum State { NO_SNAP, LEFT_SNAPPED, RIGHT_SNAPPED, BOTH_SNAPPED };
+
+  class Observer {
+   public:
+    // Called when split view state changed from |previous_state| to |state|.
+    virtual void OnSplitViewStateChanged(
+        SplitViewController::State previous_state,
+        SplitViewController::State state) {}
+  };
+
+  SplitViewController();
+  ~SplitViewController() override;
+
+  // Returns true if split view mode is supported. Currently the split view
+  // mode is only supported in maximized mode (tablet mode).
+  static bool ShouldAllowSplitView();
+
+  // Returns true if split view mode is active.
+  bool IsSplitViewModeActive() const;
+
+  // Snaps window to left/right.
+  void SetLeftWindow(aura::Window* left_window);
+  void SetRightWindow(aura::Window* right_window);
+
+  // Returns the default snapped window. It's the window that remains open until
+  // the split mode ends. It's decided by |default_snap_position_|. E.g., If
+  // |default_snap_position_| equals LEFT, then the default snapped window is
+  // |left_window_|. All the other window will open on the right side.
+  aura::Window* GetDefaultSnappedWindow();
+
+  // Gets the window bounds according to the snap state |snap_state| and the
+  // separator position |separator_position_|.
+  gfx::Rect GetSnappedWindowBoundsInParent(aura::Window* window,
+                                           State snap_state);
+  gfx::Rect GetSnappedWindowBoundsInScreen(aura::Window* window,
+                                           State snap_state);
+  gfx::Rect GetDisplayWorkAreaBoundsInParent(aura::Window* window);
+  gfx::Rect GetDisplayWorkAreaBoundsInScreen(aura::Window* window);
+
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+  // aura::WindowObserver overrides:

[varkha, 2017/06/30 14:29:35]

nit: feel free to ignore here and below - I think the preferred style now is
just '// aura::WindowObserver:'.

[xdai1, 2017/07/05 20:18:23]

Done.

+  void OnWindowDestroying(aura::Window* window) override;
+
+  // ash::wm::WindowStateObserver overrides:
+  void OnPostWindowStateTypeChange(ash::wm::WindowState* window_state,
+                                   ash::wm::WindowStateType old_type) override;
+
+  // wm::ActivationChangeObserver:
+  void OnWindowActivated(ActivationReason reason,
+                         aura::Window* gained_active,
+                         aura::Window* lost_active) override;
+
+  // ShellObserver overrides:
+  void OnOverviewModeStarting() override;
+  void OnOverviewModeEnded() override;
+
+  aura::Window* left_window() { return left_window_; }
+  aura::Window* right_window() { return right_window_; }
+  int divider_position() const { return divider_position_; }
+  State state() const { return state_; }
+
+ private:
+  friend class SplitViewControllerTest;
+
+  enum DefaultSnapPosition { LEFT, RIGHT };
+
+  // Ends the split view mode.
+  void EndSplitView();
+
+  // Stops observing |window|.
+  void StopObserving(aura::Window* window);
+
+  // Notify observers that the split view state has been changed.
+  void NotifySplitViewStateChanged(State previous_state, State state);
+
+  // Gets the window bounds according to the separator position.
+  gfx::Rect GetLeftWindowBoundsInParent(aura::Window* window);
+  gfx::Rect GetRightWindowBoundsInParent(aura::Window* window);
+  gfx::Rect GetLeftWindowBoundsInScreen(aura::Window* window);
+  gfx::Rect GetRightWindowBoundsInScreen(aura::Window* window);
+
+  // The current left/right snapped window.
+  aura::Window* left_window_ = nullptr;
+  aura::Window* right_window_ = nullptr;
+
+  // The x position of the divider between |left_window_| and |right_window_| in
+  // screen coordinates.
+  int divider_position_ = -1;
+
+  // Current snap state.
+  State state_ = NO_SNAP;
+
+  // The default snap position. It's decided by the first snapped window. If the
+  // first window was snapped left, then |default_snap_position_| equals LEFT,
+  // i.e., all the other windows will open snapped on the right side - And vice

[varkha, 2017/06/30 14:29:35]

nit: And -> and

[xdai1, 2017/07/05 20:18:23]

Done.

+  // versa.
+  DefaultSnapPosition default_snap_position_ = LEFT;
+
+  base::ObserverList<Observer> observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(SplitViewController);
+};
+
+}  // namespace ash
+
+#endif  // ASH_WM_SPLITSVIEW_SPLIT_VIEW_CONTROLLER_H_