1 files changed, 787 insertions, 0 deletions
diff --git a/js/ui/swipeTracker.js b/js/ui/swipeTracker.js
new file mode 100644
index 0000000..869f977
--- /dev/null
+++ b/js/ui/swipeTracker.js
@@ -0,0 +1,787 @@
+// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+/* exported SwipeTracker */
+
+const { Clutter, Gio, GObject, Meta } = imports.gi;
+
+const Main = imports.ui.main;
+const Params = imports.misc.params;
+
+// FIXME: ideally these values matches physical touchpad size. We can get the
+// correct values for gnome-shell specifically, since mutter uses libinput
+// directly, but GTK apps cannot get it, so use an arbitrary value so that
+// it's consistent with apps.
+const TOUCHPAD_BASE_HEIGHT = 300;
+const TOUCHPAD_BASE_WIDTH = 400;
+
+const EVENT_HISTORY_THRESHOLD_MS = 150;
+
+const SCROLL_MULTIPLIER = 10;
+
+const MIN_ANIMATION_DURATION = 100;
+const MAX_ANIMATION_DURATION = 400;
+const VELOCITY_THRESHOLD_TOUCH = 0.3;
+const VELOCITY_THRESHOLD_TOUCHPAD = 0.6;
+const DECELERATION_TOUCH = 0.998;
+const DECELERATION_TOUCHPAD = 0.997;
+const VELOCITY_CURVE_THRESHOLD = 2;
+const DECELERATION_PARABOLA_MULTIPLIER = 0.35;
+const DRAG_THRESHOLD_DISTANCE = 16;
+
+// Derivative of easeOutCubic at t=0
+const DURATION_MULTIPLIER = 3;
+const ANIMATION_BASE_VELOCITY = 0.002;
+const EPSILON = 0.005;
+
+const GESTURE_FINGER_COUNT = 3;
+
+const State = {
+    NONE: 0,
+    SCROLLING: 1,
+};
+
+const TouchpadState = {
+    NONE: 0,
+    PENDING: 1,
+    HANDLING: 2,
+    IGNORED: 3,
+};
+
+const EventHistory = class {
+    constructor() {
+        this.reset();
+    }
+
+    reset() {
+        this._data = [];
+    }
+
+    trim(time) {
+        const thresholdTime = time - EVENT_HISTORY_THRESHOLD_MS;
+        const index = this._data.findIndex(r => r.time >= thresholdTime);
+
+        this._data.splice(0, index);
+    }
+
+    append(time, delta) {
+        this.trim(time);
+
+        this._data.push({ time, delta });
+    }
+
+    calculateVelocity() {
+        if (this._data.length < 2)
+            return 0;
+
+        const firstTime = this._data[0].time;
+        const lastTime = this._data[this._data.length - 1].time;
+
+        if (firstTime === lastTime)
+            return 0;
+
+        const totalDelta = this._data.slice(1).map(a => a.delta).reduce((a, b) => a + b);
+        const period = lastTime - firstTime;
+
+        return totalDelta / period;
+    }
+};
+
+const TouchpadSwipeGesture = GObject.registerClass({
+    Properties: {
+        'enabled': GObject.ParamSpec.boolean(
+            'enabled', 'enabled', 'enabled',
+            GObject.ParamFlags.READWRITE,
+            true),
+        'orientation': GObject.ParamSpec.enum(
+            'orientation', 'orientation', 'orientation',
+            GObject.ParamFlags.READWRITE,
+            Clutter.Orientation, Clutter.Orientation.HORIZONTAL),
+    },
+    Signals: {
+        'begin':  { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE, GObject.TYPE_DOUBLE] },
+        'update': { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE, GObject.TYPE_DOUBLE] },
+        'end':    { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE] },
+    },
+}, class TouchpadSwipeGesture extends GObject.Object {
+    _init(allowedModes) {
+        super._init();
+        this._allowedModes = allowedModes;
+        this._state = TouchpadState.NONE;
+        this._cumulativeX = 0;
+        this._cumulativeY = 0;
+        this._touchpadSettings = new Gio.Settings({
+            schema_id: 'org.gnome.desktop.peripherals.touchpad',
+        });
+
+        global.stage.connectObject(
+            'captured-event::touchpad', this._handleEvent.bind(this), this);
+    }
+
+    _handleEvent(actor, event) {
+        if (event.type() !== Clutter.EventType.TOUCHPAD_SWIPE)
+            return Clutter.EVENT_PROPAGATE;
+
+        if (event.get_gesture_phase() === Clutter.TouchpadGesturePhase.BEGIN)
+            this._state = TouchpadState.NONE;
+
+        if (event.get_touchpad_gesture_finger_count() !== GESTURE_FINGER_COUNT)
+            return Clutter.EVENT_PROPAGATE;
+
+        if ((this._allowedModes & Main.actionMode) === 0)
+            return Clutter.EVENT_PROPAGATE;
+
+        if (!this.enabled)
+            return Clutter.EVENT_PROPAGATE;
+
+        if (this._state === TouchpadState.IGNORED)
+            return Clutter.EVENT_PROPAGATE;
+
+        let time = event.get_time();
+
+        const [x, y] = event.get_coords();
+        const [dx, dy] = event.get_gesture_motion_delta_unaccelerated();
+
+        if (this._state === TouchpadState.NONE) {
+            if (dx === 0 && dy === 0)
+                return Clutter.EVENT_PROPAGATE;
+
+            this._cumulativeX = 0;
+            this._cumulativeY = 0;
+            this._state = TouchpadState.PENDING;
+        }
+
+        if (this._state === TouchpadState.PENDING) {
+            this._cumulativeX += dx;
+            this._cumulativeY += dy;
+
+            const cdx = this._cumulativeX;
+            const cdy = this._cumulativeY;
+            const distance = Math.sqrt(cdx * cdx + cdy * cdy);
+
+            if (distance >= DRAG_THRESHOLD_DISTANCE) {
+                const gestureOrientation = Math.abs(cdx) > Math.abs(cdy)
+                    ? Clutter.Orientation.HORIZONTAL
+                    : Clutter.Orientation.VERTICAL;
+
+                this._cumulativeX = 0;
+                this._cumulativeY = 0;
+
+                if (gestureOrientation === this.orientation) {
+                    this._state = TouchpadState.HANDLING;
+                    this.emit('begin', time, x, y);
+                } else {
+                    this._state = TouchpadState.IGNORED;
+                    return Clutter.EVENT_PROPAGATE;
+                }
+            } else {
+                return Clutter.EVENT_PROPAGATE;
+            }
+        }
+
+        const vertical = this.orientation === Clutter.Orientation.VERTICAL;
+        let delta = vertical ? dy : dx;
+        const distance = vertical ? TOUCHPAD_BASE_HEIGHT : TOUCHPAD_BASE_WIDTH;
+
+        switch (event.get_gesture_phase()) {
+        case Clutter.TouchpadGesturePhase.BEGIN:
+        case Clutter.TouchpadGesturePhase.UPDATE:
+            if (this._touchpadSettings.get_boolean('natural-scroll'))
+                delta = -delta;
+
+            this.emit('update', time, delta, distance);
+            break;
+
+        case Clutter.TouchpadGesturePhase.END:
+        case Clutter.TouchpadGesturePhase.CANCEL:
+            this.emit('end', time, distance);
+            this._state = TouchpadState.NONE;
+            break;
+        }
+
+        return this._state === TouchpadState.HANDLING
+            ? Clutter.EVENT_STOP
+            : Clutter.EVENT_PROPAGATE;
+    }
+
+    destroy() {
+        global.stage.disconnectObject(this);
+    }
+});
+
+const TouchSwipeGesture = GObject.registerClass({
+    Properties: {
+        'distance': GObject.ParamSpec.double(
+            'distance', 'distance', 'distance',
+            GObject.ParamFlags.READWRITE,
+            0, Infinity, 0),
+        'orientation': GObject.ParamSpec.enum(
+            'orientation', 'orientation', 'orientation',
+            GObject.ParamFlags.READWRITE,
+            Clutter.Orientation, Clutter.Orientation.HORIZONTAL),
+    },
+    Signals: {
+        'begin':  { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE, GObject.TYPE_DOUBLE] },
+        'update': { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE, GObject.TYPE_DOUBLE] },
+        'end':    { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE] },
+        'cancel': { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE] },
+    },
+}, class TouchSwipeGesture extends Clutter.GestureAction {
+    _init(allowedModes, nTouchPoints, thresholdTriggerEdge) {
+        super._init();
+        this.set_n_touch_points(nTouchPoints);
+        this.set_threshold_trigger_edge(thresholdTriggerEdge);
+
+        this._allowedModes = allowedModes;
+        this._distance = global.screen_height;
+
+        global.display.connect('grab-op-begin', () => {
+            this.cancel();
+        });
+
+        this._lastPosition = 0;
+    }
+
+    get distance() {
+        return this._distance;
+    }
+
+    set distance(distance) {
+        if (this._distance === distance)
+            return;
+
+        this._distance = distance;
+        this.notify('distance');
+    }
+
+    vfunc_gesture_prepare(actor) {
+        if (!super.vfunc_gesture_prepare(actor))
+            return false;
+
+        if ((this._allowedModes & Main.actionMode) === 0)
+            return false;
+
+        let time = this.get_last_event(0).get_time();
+        let [xPress, yPress] = this.get_press_coords(0);
+        let [x, y] = this.get_motion_coords(0);
+        const [xDelta, yDelta] = [x - xPress, y - yPress];
+        const swipeOrientation = Math.abs(xDelta) > Math.abs(yDelta)
+            ? Clutter.Orientation.HORIZONTAL : Clutter.Orientation.VERTICAL;
+
+        if (swipeOrientation !== this.orientation)
+            return false;
+
+        this._lastPosition =
+            this.orientation === Clutter.Orientation.VERTICAL ? y : x;
+
+        this.emit('begin', time, xPress, yPress);
+        return true;
+    }
+
+    vfunc_gesture_progress(_actor) {
+        let [x, y] = this.get_motion_coords(0);
+        let pos = this.orientation === Clutter.Orientation.VERTICAL ? y : x;
+
+        let delta = pos - this._lastPosition;
+        this._lastPosition = pos;
+
+        let time = this.get_last_event(0).get_time();
+
+        this.emit('update', time, -delta, this._distance);
+
+        return true;
+    }
+
+    vfunc_gesture_end(_actor) {
+        let time = this.get_last_event(0).get_time();
+
+        this.emit('end', time, this._distance);
+    }
+
+    vfunc_gesture_cancel(_actor) {
+        let time = Clutter.get_current_event_time();
+
+        this.emit('cancel', time, this._distance);
+    }
+});
+
+const ScrollGesture = GObject.registerClass({
+    Properties: {
+        'enabled': GObject.ParamSpec.boolean(
+            'enabled', 'enabled', 'enabled',
+            GObject.ParamFlags.READWRITE,
+            true),
+        'orientation': GObject.ParamSpec.enum(
+            'orientation', 'orientation', 'orientation',
+            GObject.ParamFlags.READWRITE,
+            Clutter.Orientation, Clutter.Orientation.HORIZONTAL),
+        'scroll-modifiers': GObject.ParamSpec.flags(
+            'scroll-modifiers', 'scroll-modifiers', 'scroll-modifiers',
+            GObject.ParamFlags.READWRITE,
+            Clutter.ModifierType, 0),
+    },
+    Signals: {
+        'begin':  { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE, GObject.TYPE_DOUBLE] },
+        'update': { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE, GObject.TYPE_DOUBLE] },
+        'end':    { param_types: [GObject.TYPE_UINT, GObject.TYPE_DOUBLE] },
+    },
+}, class ScrollGesture extends GObject.Object {
+    _init(actor, allowedModes) {
+        super._init();
+        this._allowedModes = allowedModes;
+        this._began = false;
+        this._enabled = true;
+
+        actor.connect('scroll-event', this._handleEvent.bind(this));
+    }
+
+    get enabled() {
+        return this._enabled;
+    }
+
+    set enabled(enabled) {
+        if (this._enabled === enabled)
+            return;
+
+        this._enabled = enabled;
+        this._began = false;
+
+        this.notify('enabled');
+    }
+
+    canHandleEvent(event) {
+        if (event.type() !== Clutter.EventType.SCROLL)
+            return false;
+
+        if (event.get_scroll_source() !== Clutter.ScrollSource.FINGER &&
+            event.get_source_device().get_device_type() !== Clutter.InputDeviceType.TOUCHPAD_DEVICE)
+            return false;
+
+        if (!this.enabled)
+            return false;
+
+        if ((this._allowedModes & Main.actionMode) === 0)
+            return false;
+
+        if (!this._began && this.scrollModifiers !== 0 &&
+            (event.get_state() & this.scrollModifiers) === 0)
+            return false;
+
+        return true;
+    }
+
+    _handleEvent(actor, event) {
+        if (!this.canHandleEvent(event))
+            return Clutter.EVENT_PROPAGATE;
+
+        if (event.get_scroll_direction() !== Clutter.ScrollDirection.SMOOTH)
+            return Clutter.EVENT_PROPAGATE;
+
+        const vertical = this.orientation === Clutter.Orientation.VERTICAL;
+        const distance = vertical ? TOUCHPAD_BASE_HEIGHT : TOUCHPAD_BASE_WIDTH;
+
+        let time = event.get_time();
+        let [dx, dy] = event.get_scroll_delta();
+        if (dx === 0 && dy === 0) {
+            this.emit('end', time, distance);
+            this._began = false;
+            return Clutter.EVENT_STOP;
+        }
+
+        if (!this._began) {
+            let [x, y] = event.get_coords();
+            this.emit('begin', time, x, y);
+            this._began = true;
+        }
+
+        const delta = (vertical ? dy : dx) * SCROLL_MULTIPLIER;
+
+        this.emit('update', time, delta, distance);
+
+        return Clutter.EVENT_STOP;
+    }
+});
+
+// USAGE:
+//
+// To correctly implement the gesture, there must be handlers for the following
+// signals:
+//
+// begin(tracker, monitor)
+//   The handler should check whether a deceleration animation is currently
+//   running. If it is, it should stop the animation (without resetting
+//   progress). Then it should call:
+//   tracker.confirmSwipe(distance, snapPoints, currentProgress, cancelProgress)
+//   If it's not called, the swipe would be ignored.
+//   The parameters are:
+//    * distance: the page size;
+//    * snapPoints: an (sorted with ascending order) array of snap points;
+//    * currentProgress: the current progress;
+//    * cancelprogress: a non-transient value that would be used if the gesture
+//      is cancelled.
+//   If no animation was running, currentProgress and cancelProgress should be
+//   same. The handler may set 'orientation' property here.
+//
+// update(tracker, progress)
+//   The handler should set the progress to the given value.
+//
+// end(tracker, duration, endProgress)
+//   The handler should animate the progress to endProgress. If endProgress is
+//   0, it should do nothing after the animation, otherwise it should change the
+//   state, e.g. change the current page or switch workspace.
+//   NOTE: duration can be 0 in some cases, in this case it should finish
+//   instantly.
+
+/** A class for handling swipe gestures */
+var SwipeTracker = GObject.registerClass({
+    Properties: {
+        'enabled': GObject.ParamSpec.boolean(
+            'enabled', 'enabled', 'enabled',
+            GObject.ParamFlags.READWRITE,
+            true),
+        'orientation': GObject.ParamSpec.enum(
+            'orientation', 'orientation', 'orientation',
+            GObject.ParamFlags.READWRITE,
+            Clutter.Orientation, Clutter.Orientation.HORIZONTAL),
+        'distance': GObject.ParamSpec.double(
+            'distance', 'distance', 'distance',
+            GObject.ParamFlags.READWRITE,
+            0, Infinity, 0),
+        'allow-long-swipes': GObject.ParamSpec.boolean(
+            'allow-long-swipes', 'allow-long-swipes', 'allow-long-swipes',
+            GObject.ParamFlags.READWRITE,
+            false),
+        'scroll-modifiers': GObject.ParamSpec.flags(
+            'scroll-modifiers', 'scroll-modifiers', 'scroll-modifiers',
+            GObject.ParamFlags.READWRITE,
+            Clutter.ModifierType, 0),
+    },
+    Signals: {
+        'begin':  { param_types: [GObject.TYPE_UINT] },
+        'update': { param_types: [GObject.TYPE_DOUBLE] },
+        'end':    { param_types: [GObject.TYPE_UINT64, GObject.TYPE_DOUBLE] },
+    },
+}, class SwipeTracker extends GObject.Object {
+    _init(actor, orientation, allowedModes, params) {
+        super._init();
+        params = Params.parse(params, { allowDrag: true, allowScroll: true });
+
+        this.orientation = orientation;
+        this._allowedModes = allowedModes;
+        this._enabled = true;
+        this._distance = global.screen_height;
+        this._history = new EventHistory();
+        this._reset();
+
+        this._touchpadGesture = new TouchpadSwipeGesture(allowedModes);
+        this._touchpadGesture.connect('begin', this._beginGesture.bind(this));
+        this._touchpadGesture.connect('update', this._updateGesture.bind(this));
+        this._touchpadGesture.connect('end', this._endTouchpadGesture.bind(this));
+        this.bind_property('enabled', this._touchpadGesture, 'enabled', 0);
+        this.bind_property('orientation', this._touchpadGesture, 'orientation',
+            GObject.BindingFlags.SYNC_CREATE);
+
+        this._touchGesture = new TouchSwipeGesture(allowedModes,
+            GESTURE_FINGER_COUNT,
+            Clutter.GestureTriggerEdge.AFTER);
+        this._touchGesture.connect('begin', this._beginTouchSwipe.bind(this));
+        this._touchGesture.connect('update', this._updateGesture.bind(this));
+        this._touchGesture.connect('end', this._endTouchGesture.bind(this));
+        this._touchGesture.connect('cancel', this._cancelTouchGesture.bind(this));
+        this.bind_property('enabled', this._touchGesture, 'enabled', 0);
+        this.bind_property('orientation', this._touchGesture, 'orientation',
+            GObject.BindingFlags.SYNC_CREATE);
+        this.bind_property('distance', this._touchGesture, 'distance', 0);
+        global.stage.add_action_full('swipe', Clutter.EventPhase.CAPTURE, this._touchGesture);
+
+        if (params.allowDrag) {
+            this._dragGesture = new TouchSwipeGesture(allowedModes, 1,
+                Clutter.GestureTriggerEdge.AFTER);
+            this._dragGesture.connect('begin', this._beginGesture.bind(this));
+            this._dragGesture.connect('update', this._updateGesture.bind(this));
+            this._dragGesture.connect('end', this._endTouchGesture.bind(this));
+            this._dragGesture.connect('cancel', this._cancelTouchGesture.bind(this));
+            this.bind_property('enabled', this._dragGesture, 'enabled', 0);
+            this.bind_property('orientation', this._dragGesture, 'orientation',
+                GObject.BindingFlags.SYNC_CREATE);
+            this.bind_property('distance', this._dragGesture, 'distance', 0);
+            actor.add_action_full('drag', Clutter.EventPhase.CAPTURE, this._dragGesture);
+        } else {
+            this._dragGesture = null;
+        }
+
+        if (params.allowScroll) {
+            this._scrollGesture = new ScrollGesture(actor, allowedModes);
+            this._scrollGesture.connect('begin', this._beginGesture.bind(this));
+            this._scrollGesture.connect('update', this._updateGesture.bind(this));
+            this._scrollGesture.connect('end', this._endTouchpadGesture.bind(this));
+            this.bind_property('enabled', this._scrollGesture, 'enabled', 0);
+            this.bind_property('orientation', this._scrollGesture, 'orientation',
+                GObject.BindingFlags.SYNC_CREATE);
+            this.bind_property('scroll-modifiers',
+                this._scrollGesture, 'scroll-modifiers', 0);
+        } else {
+            this._scrollGesture = null;
+        }
+    }
+
+    /**
+     * canHandleScrollEvent:
+     * @param {Clutter.Event} scrollEvent: an event to check
+     * @returns {bool} whether the event can be handled by the tracker
+     *
+     * This function can be used to combine swipe gesture and mouse
+     * scrolling.
+     */
+    canHandleScrollEvent(scrollEvent) {
+        if (!this.enabled || this._scrollGesture === null)
+            return false;
+
+        return this._scrollGesture.canHandleEvent(scrollEvent);
+    }
+
+    get enabled() {
+        return this._enabled;
+    }
+
+    set enabled(enabled) {
+        if (this._enabled === enabled)
+            return;
+
+        this._enabled = enabled;
+        if (!enabled && this._state === State.SCROLLING)
+            this._interrupt();
+        this.notify('enabled');
+    }
+
+    get distance() {
+        return this._distance;
+    }
+
+    set distance(distance) {
+        if (this._distance === distance)
+            return;
+
+        this._distance = distance;
+        this.notify('distance');
+    }
+
+    _reset() {
+        this._state = State.NONE;
+
+        this._snapPoints = [];
+        this._initialProgress = 0;
+        this._cancelProgress = 0;
+
+        this._prevOffset = 0;
+        this._progress = 0;
+
+        this._cancelled = false;
+
+        this._history.reset();
+    }
+
+    _interrupt() {
+        this.emit('end', 0, this._cancelProgress);
+        this._reset();
+    }
+
+    _beginTouchSwipe(gesture, time, x, y) {
+        if (this._dragGesture)
+            this._dragGesture.cancel();
+
+        this._beginGesture(gesture, time, x, y);
+    }
+
+    _beginGesture(gesture, time, x, y) {
+        if (this._state === State.SCROLLING)
+            return;
+
+        this._history.append(time, 0);
+
+        let rect = new Meta.Rectangle({ x, y, width: 1, height: 1 });
+        let monitor = global.display.get_monitor_index_for_rect(rect);
+
+        this.emit('begin', monitor);
+    }
+
+    _findClosestPoint(pos) {
+        const distances = this._snapPoints.map(x => Math.abs(x - pos));
+        const min = Math.min(...distances);
+        return distances.indexOf(min);
+    }
+
+    _findNextPoint(pos) {
+        return this._snapPoints.findIndex(p => p >= pos);
+    }
+
+    _findPreviousPoint(pos) {
+        const reversedIndex = this._snapPoints.slice().reverse().findIndex(p => p <= pos);
+        return this._snapPoints.length - 1 - reversedIndex;
+    }
+
+    _findPointForProjection(pos, velocity) {
+        const initial = this._findClosestPoint(this._initialProgress);
+        const prev = this._findPreviousPoint(pos);
+        const next = this._findNextPoint(pos);
+
+        if ((velocity > 0 ? prev : next) === initial)
+            return velocity > 0 ? next : prev;
+
+        return this._findClosestPoint(pos);
+    }
+
+    _getBounds(pos) {
+        if (this.allowLongSwipes)
+            return [this._snapPoints[0], this._snapPoints[this._snapPoints.length - 1]];
+
+        const closest = this._findClosestPoint(pos);
+
+        let prev, next;
+        if (Math.abs(this._snapPoints[closest] - pos) < EPSILON) {
+            prev = next = closest;
+        } else {
+            prev = this._findPreviousPoint(pos);
+            next = this._findNextPoint(pos);
+        }
+
+        const lowerIndex = Math.max(prev - 1, 0);
+        const upperIndex = Math.min(next + 1, this._snapPoints.length - 1);
+
+        return [this._snapPoints[lowerIndex], this._snapPoints[upperIndex]];
+    }
+
+    _updateGesture(gesture, time, delta, distance) {
+        if (this._state !== State.SCROLLING)
+            return;
+
+        if ((this._allowedModes & Main.actionMode) === 0 || !this.enabled) {
+            this._interrupt();
+            return;
+        }
+
+        if (this.orientation === Clutter.Orientation.HORIZONTAL &&
+            Clutter.get_default_text_direction() === Clutter.TextDirection.RTL)
+            delta = -delta;
+
+        this._progress += delta / distance;
+        this._history.append(time, delta);
+
+        this._progress = Math.clamp(this._progress, ...this._getBounds(this._initialProgress));
+
+        this.emit('update', this._progress);
+    }
+
+    _getEndProgress(velocity, distance, isTouchpad) {
+        if (this._cancelled)
+            return this._cancelProgress;
+
+        const threshold = isTouchpad ? VELOCITY_THRESHOLD_TOUCHPAD : VELOCITY_THRESHOLD_TOUCH;
+
+        if (Math.abs(velocity) < threshold)
+            return this._snapPoints[this._findClosestPoint(this._progress)];
+
+        const decel = isTouchpad ? DECELERATION_TOUCHPAD : DECELERATION_TOUCH;
+        const slope = decel / (1.0 - decel) / 1000.0;
+
+        let pos;
+        if (Math.abs(velocity) > VELOCITY_CURVE_THRESHOLD) {
+            const c = slope / 2 / DECELERATION_PARABOLA_MULTIPLIER;
+            const x = Math.abs(velocity) - VELOCITY_CURVE_THRESHOLD + c;
+
+            pos = slope * VELOCITY_CURVE_THRESHOLD +
+                DECELERATION_PARABOLA_MULTIPLIER * x * x -
+                DECELERATION_PARABOLA_MULTIPLIER * c * c;
+        } else {
+            pos = Math.abs(velocity) * slope;
+        }
+
+        pos = pos * Math.sign(velocity) + this._progress;
+        pos = Math.clamp(pos, ...this._getBounds(this._initialProgress));
+
+        const index = this._findPointForProjection(pos, velocity);
+
+        return this._snapPoints[index];
+    }
+
+    _endTouchGesture(_gesture, time, distance) {
+        this._endGesture(time, distance, false);
+    }
+
+    _endTouchpadGesture(_gesture, time, distance) {
+        this._endGesture(time, distance, true);
+    }
+
+    _endGesture(time, distance, isTouchpad) {
+        if (this._state !== State.SCROLLING)
+            return;
+
+        if ((this._allowedModes & Main.actionMode) === 0 || !this.enabled) {
+            this._interrupt();
+            return;
+        }
+
+        this._history.trim(time);
+
+        let velocity = this._history.calculateVelocity();
+        const endProgress = this._getEndProgress(velocity, distance, isTouchpad);
+
+        velocity /= distance;
+
+        if ((endProgress - this._progress) * velocity <= 0)
+            velocity = ANIMATION_BASE_VELOCITY;
+
+        const nPoints = Math.max(1, Math.ceil(Math.abs(this._progress - endProgress)));
+        const maxDuration = MAX_ANIMATION_DURATION * Math.log2(1 + nPoints);
+
+        let duration = Math.abs((this._progress - endProgress) / velocity * DURATION_MULTIPLIER);
+        if (duration > 0)
+            duration = Math.clamp(duration, MIN_ANIMATION_DURATION, maxDuration);
+
+        this._reset();
+        this.emit('end', duration, endProgress);
+    }
+
+    _cancelTouchGesture(_gesture, time, distance) {
+        if (this._state !== State.SCROLLING)
+            return;
+
+        this._cancelled = true;
+        this._endGesture(time, distance, false);
+    }
+
+    /**
+     * confirmSwipe:
+     * @param {number} distance: swipe distance in pixels
+     * @param {number[]} snapPoints:
+     *     An array of snap points, sorted in ascending order
+     * @param {number} currentProgress: initial progress value
+     * @param {number} cancelProgress: the value to be used on cancelling
+     *
+     * Confirms a swipe. User has to call this in 'begin' signal handler,
+     * otherwise the swipe wouldn't start. If there's an animation running,
+     * it should be stopped first.
+     *
+     * @cancel_progress must always be a snap point, or a value matching
+     * some other non-transient state.
+     */
+    confirmSwipe(distance, snapPoints, currentProgress, cancelProgress) {
+        this.distance = distance;
+        this._snapPoints = snapPoints;
+        this._initialProgress = currentProgress;
+        this._progress = currentProgress;
+        this._cancelProgress = cancelProgress;
+
+        this._state = State.SCROLLING;
+    }
+
+    destroy() {
+        if (this._touchpadGesture) {
+            this._touchpadGesture.destroy();
+            delete this._touchpadGesture;
+        }
+
+        if (this._touchGesture) {
+            global.stage.remove_action(this._touchGesture);
+            delete this._touchGesture;
+        }
+    }
+});