[Tracking Patch] Unified gesture detection

content/browser/renderer_host/input/gestures/snap_scroll_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 CONTENT_BROWSER_RENDERER_HOST_INPUT_SNAP_SCROLL_CONTROLLER_H_
+#define CONTENT_BROWSER_RENDERER_HOST_INPUT_SNAP_SCROLL_CONTROLLER_H_
+
+#include "base/basictypes.h"
+
+namespace content {
+
+class MotionEvent;
+class ZoomManager;
+
+// Port of SnapScrollController.java from Chromium

[tdresser, 2014/01/08 19:18:21]

Will we still need the java version once this has landed?

+// * Changes to this class should be cosmetic only, easing fork maintenance.
+// Controls the scroll snapping behavior based on scroll updates.
+class SnapScrollController {
+ public:
+  struct Config {
+    Config();
+    ~Config();
+    int screen_width_pixels;
+    int screen_height_pixels;
+    int density_dpi;
+    float density;  // 160 DPI ~ 1, 120 DPI ~ 0.75, etc...
+  };
+
+  SnapScrollController(Config config, ZoomManager* zoom_manager);
+  ~SnapScrollController();
+
+  // Updates the snap scroll mode based on the given X and Y distance to be
+  // moved on scroll.  If the scroll update is above a threshold, the snapping
+  // behavior is reset.
+  void UpdateSnapScrollMode(float distance_x, float distance_y);
+
+  // Sets the snap scroll mode based on the event type.
+  void SetSnapScrollingMode(const MotionEvent& event);
+
+  void ResetSnapScrollMode() { snap_scroll_mode_ = SNAP_NONE; }
+  bool IsSnapVertical() const { return snap_scroll_mode_ == SNAP_VERT; }
+  bool IsSnapHorizontal() const { return snap_scroll_mode_ == SNAP_HORIZ; }
+  bool IsSnappingScrolls() const { return snap_scroll_mode_ != SNAP_NONE; }
+
+ private:
+  enum SnapMode {
+    SNAP_NONE,
+    SNAP_HORIZ,
+    SNAP_VERT,
+  };
+
+  void CalculateChannelDistance(Config config);
+
+  ZoomManager* const zoom_manager_;
+
+  float channel_distance_;
+  SnapMode snap_scroll_mode_;
+  int first_touch_x_;
+  int first_touch_y_;
+  float distance_x_;
+  float distance_y_;
+
+  DISALLOW_COPY_AND_ASSIGN(SnapScrollController);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_SNAP_SCROLL_CONTROLLER_H_