cc/input/scroll_elasticity_helper.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 CC_INPUT_SCROLL_ELASTICITY_HELPER_H_
#define CC_INPUT_SCROLL_ELASTICITY_HELPER_H_

#include "base/time/time.h"
#include "cc/base/cc_export.h"
#include "ui/gfx/geometry/vector2d_f.h"

namespace cc {

class LayerTreeHostImpl;

// ScrollElasticityHelper is based on
// WebKit/Source/platform/mac/ScrollElasticityController.h
/*
 * Copyright (C) 2011 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

// Interface between a LayerTreeHostImpl and the ScrollElasticityController. It
// would be possible, in principle, for LayerTreeHostImpl to implement this
// interface itself. This artificial boundary is introduced to reduce the amount
// of logic and state held directly inside LayerTreeHostImpl.
class CC_EXPORT ScrollElasticityHelper {
 public:
  explicit ScrollElasticityHelper(LayerTreeHostImpl* layer_tree);
  ~ScrollElasticityHelper();

  bool AllowsHorizontalStretching();
  bool AllowsVerticalStretching();
  // The amount that the view is stretched past the normal allowable bounds.
  // The "overhang" amount.
  gfx::Vector2dF StretchAmount();
  bool PinnedInDirection(const gfx::Vector2dF& direction);
  bool CanScrollHorizontally();
  bool CanScrollVertically();

  // Return the absolute scroll position, not relative to the scroll origin.
  gfx::Vector2dF AbsoluteScrollPosition();

  void ImmediateScrollBy(const gfx::Vector2dF& scroll);
  void ImmediateScrollByWithoutContentEdgeConstraints(
      const gfx::Vector2dF& scroll);
  void StartSnapRubberbandTimer();
  void StopSnapRubberbandTimer();
  void SnapRubberbandTimerFired();

  // If the current scroll position is within the overhang area, this function
  // will cause
  // the page to scroll to the nearest boundary point.
  void AdjustScrollPositionToBoundsIfNecessary();

 private:
  LayerTreeHostImpl* layer_tree_host_impl_;
  gfx::Vector2dF stretch_offset_;
  bool timer_active_;
};

}  // namespace cc

#endif  // CC_INPUT_SCROLL_ELASTICITY_HELPER_H_