Split View Mode: Support for the 2-finger bezel scroll.

athena/wm/bezel_controller.h

+// 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.
+
+#ifndef ATHENA_WM_BEZEL_CONTROLLER_H_
+#define ATHENA_WM_BEZEL_CONTROLLER_H_
+
+#include "ui/events/event_handler.h"
+
+namespace aura {
+class Window;
+}
+
+namespace gfx {
+class PointF;
+}
+
+namespace ui {
+class EventTarget;
+}
+
+namespace athena {
+
+// Responsible for detecting bezel gestures and notifying the delegate(s)
+// subscribed to them.
+class BezelController : public ui::EventHandler {
+ public:
+  enum Bezel { BEZEL_NONE, BEZEL_LEFT, BEZEL_RIGHT, BEZEL_TOP, BEZEL_BOTTOM };
+
+  // Responsible for handling scroll gestures initiated from the bezel.
+  // Two touch points are need to perform the bezel scroll gesture from
+  // the left and right bezel.
+  class ScrollDelegate {
+   public:
+    virtual ~ScrollDelegate() {}
+
+    // Beginning of a bezel scroll gesture started from the |bezel|.
+    virtual void ScrollBegin(Bezel bezel, float delta) = 0;
+
+    // End of the current bezel scroll
+    virtual void ScrollEnd() = 0;
+
+    // Update of the scroll position for the currently active bezel scroll.
+    virtual void ScrollUpdate(float delta) = 0;
+
+    // Should return false if the delegate isn't going to react to the scroll
+    // events.
+    virtual bool CanScroll() = 0;
+  };
+
+  explicit BezelController(aura::Window* container);
+  virtual ~BezelController() {}
+
+  // Set the delegate to handle the gestures from left and right bezels.
+  // Two touch points are need to perform the bezel scroll gesture from
+  // the left and right bezel.
+  void set_left_right_delegate(ScrollDelegate* delegate) {
+    left_right_delegate_ = delegate;
+  }
+
+ private:
+  enum State {
+    NONE,
+    IGNORE_CURRENT_SCROLL,
+    BEZEL_GESTURE_STARTED,
+    BEZEL_SCROLLING_ONE_FINGER,
+    BEZEL_SCROLLING_TWO_FINGERS,
+  };
+
+  // Calculates the distance from |position| to the |bezel|.
+  float GetDistance(const gfx::PointF& position, Bezel bezel);
+
+  // |scroll_position| only needs to be passed in the scrolling state
+  void SetState(State state, const gfx::PointF& scroll_position);
+
+  // Returns the bezel corresponding to the |location| or BEZEL_NONE if the
+  // location is outside of the bezel area.
+  Bezel GetBezel(const gfx::PointF& location);
+
+  // ui::EventHandler overrides
+  virtual void OnGestureEvent(ui::GestureEvent* event) OVERRIDE;
+
+  aura::Window* container_;
+
+  State state_;
+
+  // The bezel where the currently active scroll was started.
+  Bezel scroll_bezel_;
+
+  // The target of the bezel scroll gesture. Used to filter out other gestures
+  // when the bezel scroll is in progress.
+  ui::EventTarget* scroll_target_;
+
+  // Responsible for handling gestures started from the left and right bezels.
+  // Not owned.
+  ScrollDelegate* left_right_delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(BezelController);
+};
+
+}  // namespace athena
+
+#endif  // ATHENA_WM_BEZEL_CONTROLLER_H_