content/browser/android/overscroll_refresh.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "content/browser/android/overscroll_refresh.h"
   6
   7 #include "base/logging.h"
   8
   9 namespace content {
  10 namespace {
  11
  12 // Experimentally determined constant used to allow activation even if touch
  13 // release results in a small upward fling (quite common during a slow scroll).
  14 const float kMinFlingVelocityForActivation = -500.f;
  15
  16 }  // namespace
  17
  18 OverscrollRefresh::OverscrollRefresh(OverscrollRefreshHandler* handler)
  19     : scrolled_to_top_(true),
  20       overflow_y_hidden_(false),
  21       scroll_consumption_state_(DISABLED),
  22       handler_(handler) {
  23   DCHECK(handler);
  24 }
  25
  26 OverscrollRefresh::~OverscrollRefresh() {
  27 }
  28
  29 void OverscrollRefresh::Reset() {
  30   scroll_consumption_state_ = DISABLED;
  31   handler_->PullReset();
  32 }
  33
  34 void OverscrollRefresh::OnScrollBegin() {
  35   ReleaseWithoutActivation();
  36   if (scrolled_to_top_ && !overflow_y_hidden_)
  37     scroll_consumption_state_ = AWAITING_SCROLL_UPDATE_ACK;
  38 }
  39
  40 void OverscrollRefresh::OnScrollEnd(const gfx::Vector2dF& scroll_velocity) {
  41   bool allow_activation = scroll_velocity.y() > kMinFlingVelocityForActivation;
  42   Release(allow_activation);
  43 }
  44
  45 void OverscrollRefresh::OnScrollUpdateAck(bool was_consumed) {
  46   if (scroll_consumption_state_ != AWAITING_SCROLL_UPDATE_ACK)
  47     return;
  48
  49   if (was_consumed) {
  50     scroll_consumption_state_ = DISABLED;
  51     return;
  52   }
  53
  54   scroll_consumption_state_ = handler_->PullStart() ? ENABLED : DISABLED;
  55 }
  56
  57 bool OverscrollRefresh::WillHandleScrollUpdate(
  58     const gfx::Vector2dF& scroll_delta) {
  59   switch (scroll_consumption_state_) {
  60     case DISABLED:
  61       return false;
  62
  63     case AWAITING_SCROLL_UPDATE_ACK:
  64       // If the initial scroll motion is downward, never allow activation.
  65       if (scroll_delta.y() <= 0)
  66         scroll_consumption_state_ = DISABLED;
  67       return false;
  68
  69     case ENABLED:
  70       handler_->PullUpdate(scroll_delta.y());
  71       return true;
  72   }
  73
  74   NOTREACHED() << "Invalid overscroll state: " << scroll_consumption_state_;
  75   return false;
  76 }
  77
  78 void OverscrollRefresh::ReleaseWithoutActivation() {
  79   bool allow_activation = false;
  80   Release(allow_activation);
  81 }
  82
  83 bool OverscrollRefresh::IsActive() const {
  84   return scroll_consumption_state_ == ENABLED;
  85 }
  86
  87 bool OverscrollRefresh::IsAwaitingScrollUpdateAck() const {
  88   return scroll_consumption_state_ == AWAITING_SCROLL_UPDATE_ACK;
  89 }
  90
  91 void OverscrollRefresh::OnFrameUpdated(
  92     const gfx::Vector2dF& content_scroll_offset,
  93     bool root_overflow_y_hidden) {
  94   scrolled_to_top_ = content_scroll_offset.y() == 0;
  95   overflow_y_hidden_ = root_overflow_y_hidden;
  96 }
  97
  98 void OverscrollRefresh::Release(bool allow_refresh) {
  99   if (scroll_consumption_state_ == ENABLED)
 100     handler_->PullRelease(allow_refresh);
 101   scroll_consumption_state_ = DISABLED;
 102 }
 103
 104 }  // namespace content