overscroll_refresh.cc

// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "ui/android/overscroll_refresh.h"

#include <ostream>

#include "base/check.h"
#include "base/notreached.h"
#include "cc/input/overscroll_behavior.h"
#include "ui/android/overscroll_refresh_handler.h"
#include "ui/gfx/geometry/point_f.h"

namespace ui {
namespace {

// Experimentally determined constant used to allow activation even if touch
// release results in a small upward fling (quite common during a slow scroll).
const float kMinFlingVelocityForActivation = -500.f;

// Weighted value used to determine whether a scroll should trigger vertical
// scroll or horizontal navigation.
const float kWeightAngle30 = 1.73f;

}  // namespace

OverscrollRefresh::OverscrollRefresh(OverscrollRefreshHandler* handler,
                                     float edge_width)
    : scrolled_to_top_(true),
      top_at_scroll_start_(true),
      overflow_y_hidden_(false),
      scroll_consumption_state_(DISABLED),
      edge_width_(edge_width),
      handler_(handler) {
  DCHECK(handler);
}

OverscrollRefresh::OverscrollRefresh()
    : scrolled_to_top_(true),
      overflow_y_hidden_(false),
      scroll_consumption_state_(DISABLED),
      edge_width_(kDefaultNavigationEdgeWidth * 1.f),
      handler_(nullptr) {}

OverscrollRefresh::~OverscrollRefresh() {
}

void OverscrollRefresh::Reset() {
  scroll_consumption_state_ = DISABLED;
  cumulative_scroll_.set_x(0);
  cumulative_scroll_.set_y(0);
  handler_->PullReset();
}

void OverscrollRefresh::OnScrollBegin(const gfx::PointF& pos) {
  scroll_begin_x_ = pos.x();
  scroll_begin_y_ = pos.y();
  top_at_scroll_start_ = scrolled_to_top_;
  ReleaseWithoutActivation();
  scroll_consumption_state_ = AWAITING_SCROLL_UPDATE_ACK;
}

void OverscrollRefresh::OnScrollEnd(const gfx::Vector2dF& scroll_velocity) {
  bool allow_activation = scroll_velocity.y() > kMinFlingVelocityForActivation;
  Release(allow_activation);
}

void OverscrollRefresh::OnOverscrolled(const cc::OverscrollBehavior& behavior) {
  if (scroll_consumption_state_ != AWAITING_SCROLL_UPDATE_ACK)
    return;

  float ydelta = cumulative_scroll_.y();
  float xdelta = cumulative_scroll_.x();
  bool in_y_direction = std::abs(ydelta) > std::abs(xdelta);
  bool in_x_direction = std::abs(ydelta) * kWeightAngle30 < std::abs(xdelta);
  OverscrollAction type = OverscrollAction::NONE;
  bool navigate_forward = false;
  if (ydelta > 0 && in_y_direction) {
    // Pull-to-refresh. Check overscroll-behavior-y
    if (behavior.y != cc::OverscrollBehavior::Type::kAuto) {
      Reset();
      return;
    }
    type = OverscrollAction::PULL_TO_REFRESH;
  } else if (in_x_direction &&
             (scroll_begin_x_ < edge_width_ ||
              viewport_width_ - scroll_begin_x_ < edge_width_)) {
    // Swipe-to-navigate. Check overscroll-behavior-x
    if (behavior.x != cc::OverscrollBehavior::Type::kAuto) {
      Reset();
      return;
    }
    type = OverscrollAction::HISTORY_NAVIGATION;
    navigate_forward = xdelta < 0;
  }

  if (type != OverscrollAction::NONE) {
    scroll_consumption_state_ =
        handler_->PullStart(type, scroll_begin_x_, scroll_begin_y_,
                            navigate_forward)
            ? ENABLED
            : DISABLED;
  }
}

bool OverscrollRefresh::WillHandleScrollUpdate(
    const gfx::Vector2dF& scroll_delta) {
  switch (scroll_consumption_state_) {
    case DISABLED:
      return false;

    case AWAITING_SCROLL_UPDATE_ACK:
      // Check applies for the pull-to-refresh condition only.
      if (std::abs(scroll_delta.y()) > std::abs(scroll_delta.x())) {
        // If the initial scroll motion is downward, or we're in other cases
        // where activation shouldn't have happened, stop here.
        if (scroll_delta.y() <= 0 || !top_at_scroll_start_ ||
            overflow_y_hidden_) {
          scroll_consumption_state_ = DISABLED;
          return false;
        }
      }
      cumulative_scroll_.Add(scroll_delta);
      return false;

    case ENABLED:
      handler_->PullUpdate(scroll_delta.x(), scroll_delta.y());
      return true;
  }

  NOTREACHED() << "Invalid overscroll state: " << scroll_consumption_state_;
  return false;
}

void OverscrollRefresh::ReleaseWithoutActivation() {
  bool allow_activation = false;
  Release(allow_activation);
}

bool OverscrollRefresh::IsActive() const {
  return scroll_consumption_state_ == ENABLED;
}

bool OverscrollRefresh::IsAwaitingScrollUpdateAck() const {
  return scroll_consumption_state_ == AWAITING_SCROLL_UPDATE_ACK;
}

void OverscrollRefresh::OnFrameUpdated(const gfx::SizeF& viewport_size,
                                       const gfx::PointF& content_scroll_offset,
                                       bool root_overflow_y_hidden) {
  viewport_width_ = viewport_size.width();
  scrolled_to_top_ = content_scroll_offset.y() == 0;
  overflow_y_hidden_ = root_overflow_y_hidden;
}

void OverscrollRefresh::Release(bool allow_refresh) {
  if (scroll_consumption_state_ == ENABLED)
    handler_->PullRelease(allow_refresh);
  scroll_consumption_state_ = DISABLED;
  cumulative_scroll_.set_x(0);
  cumulative_scroll_.set_y(0);
}

}  // namespace ui