cc/input/layer_scroll_offset_delegate.h

// Copyright 2013 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_LAYER_SCROLL_OFFSET_DELEGATE_H_
#define CC_INPUT_LAYER_SCROLL_OFFSET_DELEGATE_H_

#include "base/basictypes.h"
#include "ui/gfx/geometry/scroll_offset.h"
#include "ui/gfx/geometry/size_f.h"

namespace cc {

// The LayerScrollOffsetDelegate allows for the embedder to take ownership of
// the scroll offset of the root layer.
//
// The LayerScrollOffsetDelegate is only used on the impl thread.
class LayerScrollOffsetDelegate {
 public:
  // This is called by the compositor to query the current scroll offset of the
  // layer.
  // There is no requirement that the return values of this method are
  // stable in time (two subsequent calls may yield different results).
  // The return value is not required to be related to the values passed in to
  // the SetTotalScrollOffset method in any way however it is required to be no
  // more than the value passed to the most recent SetMaxScrollOffset call.
  virtual gfx::ScrollOffset GetTotalScrollOffset() = 0;

  // This is called by the compositor to notify the delegate of any change to
  // the following parameters:
  // |total_scroll_offset| current scroll offset of the root layer,
  // |max_scroll_offset| total scroll offset upper bound for the root layer,
  // |scrollable_size| root layer scrollable size,
  // |page_scale_factor| current page scale,
  // |min_page_scale_factor| page scale lower limit,
  // |max_page_scale_factor| page scale upper limit.
  virtual void UpdateRootLayerState(
      const gfx::ScrollOffset& total_scroll_offset,
      const gfx::ScrollOffset& max_scroll_offset,
      const gfx::SizeF& scrollable_size,
      float page_scale_factor,
      float min_page_scale_factor,
      float max_page_scale_factor) = 0;

  // This is called by the compositor to check whether a delegate-managed fling
  // is active or not.
  virtual bool IsExternalFlingActive() const = 0;

 protected:
  LayerScrollOffsetDelegate() {}
  virtual ~LayerScrollOffsetDelegate() {}

 private:
  DISALLOW_COPY_AND_ASSIGN(LayerScrollOffsetDelegate);
};

}  // namespace cc

#endif  // CC_INPUT_LAYER_SCROLL_OFFSET_DELEGATE_H_