Touch gestures for System Tray/ IME/ Stylus/ Notifications

ash/system/tray_drag_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_SYSTEM_TRAY_DRAG_CONTROLLER_H_
+#define ASH_SYSTEM_TRAY_DRAG_CONTROLLER_H_
+
+#include "ash/ash_export.h"
+#include "ash/shelf/shelf.h"
+#include "ui/views/view.h"
+
+namespace ash {
+class TrayBackgroundView;
+
+// The TrayDragController helps to process the swiping events that happened on
+// TrayBackgroundView or TrayBubbleView. Not all the TrayBackgroundView can be
+// dragged currently. Only ImeMenuTray, SystemTray, PaletteTray,
+// WebNotificationTray and their's accosiated tray bubbles can be dragged.

[tdanderson, 2017/07/18 16:38:05]

Thanks, this is a nice description. One small typo nit, though: "their
associated".

[minch1, 2017/07/18 20:01:52]

Done.

+class ASH_EXPORT TrayDragController {
+ public:
+  // The threshold of the velocity of the fling event.
+  static constexpr float kFlingVelocity = 100.0f;
+
+  explicit TrayDragController(Shelf* shelf);
+
+  // Processes a gesture event and updates the dragging state of the bubble when
+  // appropriate.
+  void ProcessGestureEvent(ui::GestureEvent* event,
+                           TrayBackgroundView* tray_view);
+
+ private:
+  // Gesture related functions:
+  bool StartGestureDrag(const ui::GestureEvent& gesture);
+  void UpdateGestureDrag(const ui::GestureEvent& gesture);
+  void CompleteGestureDrag(const ui::GestureEvent& gesture);
+
+  // Update the bounds of the tray bubble according to
+  // |gesture_drag_amount_|.
+  void UpdateBubbleBounds();
+
+  // Return true if the bubble should be shown (i.e., animated upward to
+  // be made fully visible) after a sequence of scroll events terminated by
+  // |sequence_end|. Otherwise return false, indicating that the
+  // partially-visible bubble should be animated downward and made fully
+  // hidden.
+  bool ShouldShowBubbleAfterScrollSequence(
+      const ui::GestureEvent& sequence_end);
+
+  // The shelf containing the TrayBackgroundView.
+  Shelf* shelf_;
+
+  // The specific TrayBackgroundView that dragging happened on. e.g, SystemTray.
+  TrayBackgroundView* tray_view_ = nullptr;
+
+  // The original bounds of the tray bubble.
+  gfx::Rect tray_bubble_bounds_;
+
+  // Tracks the amount of the drag. Only valid if |is_in_drag_| is true.
+  float gesture_drag_amount_ = 0.f;
+
+  // True if the user is in the process of gesture-dragging on
+  // TrayBackgroundView to open the tray bubble, or on the already-opened
+  // TrayBubbleView to close it. Otherwise false.
+  bool is_in_drag_ = false;
+
+  // True if the dragging happened on the bubble view, false if it happened on
+  // the tray view. Note, only valid if |is_in_drag_| is true.
+  bool is_on_bubble_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(TrayDragController);
+};
+
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_TRAY_DRAG_CONTROLLER_H_