VR: Improve scrolling

chrome/browser/android/vr_shell/vr_controller.h

 // 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.
 
 #ifndef CHROME_BROWSER_ANDROID_VR_SHELL_VR_CONTROLLER_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_VR_CONTROLLER_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 111 matching lines @@
   GestureDetectorState state_;
 
   std::unique_ptr<gvr::ControllerApi> controller_api_;
 
   // The last controller state (updated once per frame).
   std::unique_ptr<gvr::ControllerState> controller_state_;
 
   float last_qx_;
   bool pinch_started_;
   bool zoom_in_progress_ = false;
+  bool touch_position_changed_ = false;
 
+  // Current touch info after the extrapolation.
   std::unique_ptr<TouchInfo> touch_info_;
 
+  // Current touch position reported by touchpad.
+  std::unique_ptr<TouchPoint> touch_point_;

[bshe, 2017/01/09 19:38:54]

Is it possible to use cur_touch_point_ directly to eliminate the need for
touch_point_?

[asimjour1, 2017/01/11 21:59:45]

It is possible. But more changes would be needed. 
prev_touch_point_ is updated only when the a new touch_point is reported or
extrapolation happens. Also, replacing the prev_touch_point_ with
cur_touch_point_ should be moved to the end of each controller update.

I'll make a bug and address this in another CL.

+
   // A pointer storing the touch point from previous frame.
   std::unique_ptr<TouchPoint> prev_touch_point_;
 
   // A pointer storing the touch point from current frame.
   std::unique_ptr<TouchPoint> cur_touch_point_;
 
   // Initial touch point.
   std::unique_ptr<TouchPoint> init_touch_point_;
 
   // Overall velocity
   gvr::Vec2f overall_velocity_;
 
+  // Last velocity that is used for fling and direction detection
+  gvr::Vec2f last_velocity_;
+
   // Displacement of the touch point from the previews to the current touch
   gvr::Vec2f displacement_;
 
   int64_t last_touch_timestamp_ = 0;
   int64_t last_timestamp_nanos_ = 0;
 
+  // Number of consecutively extrapolated touch points
+  int extrapolated_touch_ = 0;
+
   DISALLOW_COPY_AND_ASSIGN(VrController);
 };
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_VR_CONTROLLER_H_