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// Copyright (c) 2012 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.
#include "base/compiler_specific.h"
#include "base/macros.h"
#include "base/optional.h"
#include "base/time/time.h"
#include "cc/input/overscroll_behavior.h"
#include "content/common/content_export.h"
#include "third_party/blink/public/platform/web_gesture_event.h"
#include "third_party/blink/public/platform/web_input_event.h"
#include "ui/events/blink/did_overscroll_params.h"
namespace content {
class OverscrollControllerDelegate;
class OverscrollControllerTest;
class RenderWidgetHostViewAuraOverscrollTest;
// Indicates the direction that the scroll is heading in relative to the screen,
// with the top being NORTH.
enum OverscrollMode {
// Indicates the source device that was used to trigger the overscroll gesture.
enum class OverscrollSource {
// When a page is scrolled beyond the scrollable region, it will trigger an
// overscroll gesture. This controller receives the events that are dispatched
// to the renderer, and the ACKs of events, and updates the overscroll gesture
// status accordingly.
// Exported for testing.
class CONTENT_EXPORT OverscrollController {
virtual ~OverscrollController();
// This must be called when dispatching any event from the
// RenderWidgetHostView so that the state of the overscroll gesture can be
// updated properly. Returns true if the event was handled, in which case
// further processing should cease.
bool WillHandleEvent(const blink::WebInputEvent& event);
// This is called whenever an overscroll event is generated on the renderer
// side. This is called before ReceivedEventAck. The params contains an
// OverscrollBehavior that can prevent overscroll navigation.
void OnDidOverscroll(const ui::DidOverscrollParams& params);
// This must be called when the ACK for any event comes in. This updates the
// overscroll gesture status as appropriate.
// Virtual for testing.
virtual void ReceivedEventACK(const blink::WebInputEvent& event,
bool processed);
OverscrollMode overscroll_mode() const { return overscroll_mode_; }
void set_delegate(OverscrollControllerDelegate* delegate) {
delegate_ = delegate;
// Resets internal states.
void Reset();
// Cancels any in-progress overscroll (and calls OnOverscrollModeChange on the
// delegate if necessary), and resets internal states.
void Cancel();
friend class OverscrollControllerTest;
friend class RenderWidgetHostViewAuraOverscrollTest;
// Different scrolling states.
enum class ScrollState {
// Either a mouse-wheel or a gesture-scroll-update event is consumed by the
// renderer in which case no overscroll should be initiated until the end of
// the user interaction.
// Overscroll controller has initiated overscrolling and will consume all
// subsequent gesture-scroll-update events, preventing them from being
// forwarded to the renderer.
// Returns true if the event indicates that the in-progress overscroll gesture
// can now be completed.
bool DispatchEventCompletesAction(const blink::WebInputEvent& event) const;
// Returns true to indicate that dispatching the event should reset the
// overscroll gesture status.
bool DispatchEventResetsState(const blink::WebInputEvent& event) const;
// Processes an event to update the internal state for overscroll. Returns
// true if the state is updated, false otherwise.
bool ProcessEventForOverscroll(const blink::WebInputEvent& event);
// Processes horizontal overscroll. This can update both the overscroll mode
// and the over scroll amount (i.e. |overscroll_mode_|, |overscroll_delta_x_|
// and |overscroll_delta_y_|). Returns true if overscroll was handled by the
// delegate.
bool ProcessOverscroll(float delta_x,
float delta_y,
bool is_touchpad,
bool is_inertial);
// Completes the desired action from the current gesture.
void CompleteAction();
// Sets the overscroll mode and triggers callback in the delegate when
// appropriate. When a new overscroll is started (i.e. when |new_mode| is not
// equal to OVERSCROLL_NONE), |source| will be set to the device that
// triggered the overscroll gesture.
void SetOverscrollMode(OverscrollMode new_mode, OverscrollSource source);
// Whether this inertial event should be filtered out by the controller.
bool ShouldIgnoreInertialEvent(const blink::WebInputEvent& event) const;
// Whether this event should be processed or not handled by the controller.
bool ShouldProcessEvent(const blink::WebInputEvent& event);
// Helper function to reset |scroll_state_| and |locked_mode_|.
void ResetScrollState();
// Current value of overscroll-behavior CSS property for the root element of
// the page.
cc::OverscrollBehavior behavior_;
// The current state of overscroll gesture.
OverscrollMode overscroll_mode_ = OVERSCROLL_NONE;
// When set to something other than OVERSCROLL_NONE, the overscroll cannot
// switch to any other mode, except to OVERSCROLL_NONE. This is set when an
// overscroll is started until the touch sequence is completed.
OverscrollMode locked_mode_ = OVERSCROLL_NONE;
// Source of the current overscroll gesture.
OverscrollSource overscroll_source_ = OverscrollSource::NONE;
// Current scrolling state.
ScrollState scroll_state_ = ScrollState::NONE;
// The amount of overscroll in progress. These values are invalid when
// |overscroll_mode_| is set to OVERSCROLL_NONE.
float overscroll_delta_x_ = 0.f;
float overscroll_delta_y_ = 0.f;
// The delegate that receives the overscroll updates. The delegate is not
// owned by this controller.
OverscrollControllerDelegate* delegate_ = nullptr;
// A inertial scroll (fling) event may complete an overscroll gesture and
// navigate to a new page or cancel the overscroll animation. In both cases
// inertial scroll can continue to generate scroll-update events. These events
// need to be ignored.
bool ignore_following_inertial_events_ = false;
// Specifies whether last overscroll was ignored, either due to a command line
// flag or because cool off period had not passed.
bool overscroll_ignored_ = false;
// Timestamp for the end of the last ignored scroll sequence.
base::TimeTicks last_ignored_scroll_time_;
// Time between the end of the last ignored scroll sequence and the beginning
// of the current one.
base::TimeDelta time_since_last_ignored_scroll_;
// On Windows, we don't generate the inertial events (fling) but receive them
// from Win API. In some cases, we get a long tail of inertial events for a
// couple of seconds. The overscroll animation feels like stuck in these
// cases. So we only process 0.3 second inertial events then cancel the
// overscroll if it is not completed yet.
// Timestamp for the first inertial event (fling) in current stream.
base::Optional<base::TimeTicks> first_inertial_event_time_;
} // namespace content