cc/input/scroll_state.h

// Copyright 2015 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_STATE_H_
#define CC_INPUT_SCROLL_STATE_H_

#include <list>

#include "cc/base/cc_export.h"

namespace cc {

class LayerImpl;

// ScrollState is based on the proposal for scroll customization in blink, found
// here: https://goo.gl/1ipTpP.
class CC_EXPORT ScrollState {
 public:
  ScrollState(double delta_x,
              double delta_y,
              int start_position_x,
              int start_position_y,
              bool should_propagate,
              bool delta_consumed_for_scroll_sequence,
              bool is_direct_manipulation);
  ~ScrollState();

  // Reduce deltas by x, y.
  void ConsumeDelta(double x, double y);
  // Pops the first layer off of |scroll_chain_| and calls
  // |DistributeScroll| on it.
  void DistributeToScrollChainDescendant();
  // Positive when scrolling left.
  double delta_x() const { return delta_x_; }
  // Positive when scrolling up.
  double delta_y() const { return delta_y_; }
  // The location the scroll started at. For touch, the starting
  // position of the finger. For mouse, the location of the cursor.
  int start_position_x() const { return start_position_x_; }
  int start_position_y() const { return start_position_y_; }

  // True if this scroll is allowed to bubble upwards.
  bool should_propagate() const { return should_propagate_; }
  // True if the user interacts directly with the screen, e.g., via touch.
  bool is_direct_manipulation() const { return is_direct_manipulation_; }

  void set_scroll_chain(const std::list<LayerImpl*>& scroll_chain) {
    scroll_chain_ = scroll_chain;
  }

  void set_current_native_scrolling_layer(LayerImpl* layer) {
    current_native_scrolling_layer_ = layer;
  }

  LayerImpl* current_native_scrolling_layer() const {
    return current_native_scrolling_layer_;
  }

  bool delta_consumed_for_scroll_sequence() const {
    return delta_consumed_for_scroll_sequence_;
  }

  bool FullyConsumed() const { return !delta_x_ && !delta_y_; }

  void set_caused_scroll(bool x, bool y) {
    caused_scroll_x_ |= x;
    caused_scroll_y_ |= y;
  }

  bool caused_scroll_x() const { return caused_scroll_x_; }
  bool caused_scroll_y() const { return caused_scroll_y_; }

 private:
  ScrollState();
  double delta_x_;
  double delta_y_;
  double start_position_x_;
  double start_position_y_;

  bool should_propagate_;

  // The last layer to respond to a scroll, or null if none exists.
  LayerImpl* current_native_scrolling_layer_;
  // Whether the scroll sequence has had any delta consumed, in the
  // current frame, or any child frames.
  bool delta_consumed_for_scroll_sequence_;
  // True if the user interacts directly with the display, e.g., via
  // touch.
  bool is_direct_manipulation_;
  // TODO(tdresser): ScrollState shouldn't need to keep track of whether or not
  // this ScrollState object has caused a scroll. Ideally, any native scroller
  // consuming delta has caused a scroll. Currently, there are some cases where
  // we consume delta without scrolling, such as in
  // |Viewport::AdjustOverscroll|. Once these cases are fixed, we should get rid
  // of |caused_scroll_*_|. See crbug.com/510045 for details.
  bool caused_scroll_x_;
  bool caused_scroll_y_;

  // TODO(tdresser): Change LayerImpl* to an abstract scrollable type. See
  // crbug.com/476553 for detail on the effort to unify impl and main thread
  // scrolling, which will require an abstract scrollable type.
  std::list<LayerImpl*> scroll_chain_;
};

}  // namespace cc

#endif  // CC_INPUT_SCROLL_STATE_H_