[gnome-shell/wip/exalm/gestures-part-3: 5/6] appDisplay: Use SwipeTracker

[Florian Müllner <fmuellner src gnome org>]

commit 3e6bcbb486e38877b672627ad33923b2e6aef277
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Sun Jun 30 17:15:37 2019 +0500

    appDisplay: Use SwipeTracker
    
    Replace existing panning and touchpad scrolling by SwipeTracker.
    
    Since SwipeTracker only references one actor, redirect scroll events
    from page indicators to the main scroll view.
    
    Change programmatic scroll animation to use easeOutCubic interpolator
    to match the gesture.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/826

 js/ui/appDisplay.js | 111 ++++++++++++++++++++++------------------------------
 1 file changed, 47 insertions(+), 64 deletions(-)
---
diff --git a/js/ui/appDisplay.js b/js/ui/appDisplay.js
index 0156877e8f..da8f562195 100644
--- a/js/ui/appDisplay.js
+++ b/js/ui/appDisplay.js
@@ -13,6 +13,7 @@ const Main = imports.ui.main;
 const PageIndicators = imports.ui.pageIndicators;
 const PopupMenu = imports.ui.popupMenu;
 const Search = imports.ui.search;
+const SwipeTracker = imports.ui.swipeTracker;
 const Params = imports.misc.params;
 const Util = imports.misc.util;
 const SystemActions = imports.misc.systemActions;
@@ -327,7 +328,9 @@ var AllView = GObject.registerClass({
             (indicators, pageIndex) => {
                 this.goToPage(pageIndex);
             });
-        this._pageIndicators.connect('scroll-event', this._onScroll.bind(this));
+        this._pageIndicators.connect('scroll-event', (actor, event) => {
+            this._scrollView.event(event, false);
+        });
         this.add_actor(this._pageIndicators);
 
         this._folderIcons = [];
@@ -353,13 +356,12 @@ var AllView = GObject.registerClass({
 
         this._scrollView.connect('scroll-event', this._onScroll.bind(this));
 
-        let panAction = new Clutter.PanAction({ interpolate: false });
-        panAction.connect('pan', this._onPan.bind(this));
-        panAction.connect('gesture-cancel', this._onPanEnd.bind(this));
-        panAction.connect('gesture-end', this._onPanEnd.bind(this));
-        this._panAction = panAction;
-        this._scrollView.add_action(panAction);
-        this._panning = false;
+        this._swipeTracker = new SwipeTracker.SwipeTracker(
+            this._scrollView, Shell.ActionMode.OVERVIEW);
+        this._swipeTracker.connect('begin', this._swipeBegin.bind(this));
+        this._swipeTracker.connect('update', this._swipeUpdate.bind(this));
+        this._swipeTracker.connect('end', this._swipeEnd.bind(this));
+
         this._clickAction = new Clutter.ClickAction();
         this._clickAction.connect('clicked', () => {
             if (!this._currentPopup)
@@ -424,6 +426,7 @@ var AllView = GObject.registerClass({
         this._keyPressEventId =
             global.stage.connect('key-press-event',
                 this._onKeyPressEvent.bind(this));
+        this._swipeTracker.enabled = true;
         super.vfunc_map();
     }
 
@@ -432,6 +435,7 @@ var AllView = GObject.registerClass({
             global.stage.disconnect(this._keyPressEventId);
             this._keyPressEventId = 0;
         }
+        this._swipeTracker.enabled = false;
         super.vfunc_unmap();
     }
 
@@ -577,7 +581,7 @@ var AllView = GObject.registerClass({
         return this._grid.getPageY(this._grid.currentPage);
     }
 
-    goToPage(pageNumber) {
+    goToPage(pageNumber, animate = true) {
         pageNumber = clamp(pageNumber, 0, this._grid.nPages() - 1);
 
         if (this._grid.currentPage == pageNumber && this._displayingPopup && this._currentPopup)
@@ -592,42 +596,16 @@ var AllView = GObject.registerClass({
             return;
         }
 
-        let velocity;
-        if (!this._panning)
-            velocity = 0;
-        else
-            velocity = Math.abs(this._panAction.get_velocity(0)[2]);
-        // Tween the change between pages.
-        // If velocity is not specified (i.e. scrolling with mouse wheel),
-        // use the same speed regardless of original position
-        // if velocity is specified, it's in pixels per milliseconds
-        let diffToPage = this._diffToPage(pageNumber);
-        let childBox = this._scrollView.get_allocation_box();
-        let totalHeight = childBox.y2 - childBox.y1;
-        let time;
-        // Only take the velocity into account on page changes, otherwise
-        // return smoothly to the current page using the default velocity
-        if (this._grid.currentPage != pageNumber) {
-            let minVelocity = totalHeight / PAGE_SWITCH_TIME;
-            velocity = Math.max(minVelocity, velocity);
-            time = diffToPage / velocity;
-        } else {
-            time = PAGE_SWITCH_TIME * diffToPage / totalHeight;
-        }
-        // When changing more than one page, make sure to not take
-        // longer than PAGE_SWITCH_TIME
-        time = Math.min(time, PAGE_SWITCH_TIME);
+        if (this._grid.currentPage === pageNumber)
+            return;
 
         this._grid.currentPage = pageNumber;
-        this._adjustment.ease(this._grid.getPageY(pageNumber), {
-            mode: Clutter.AnimationMode.EASE_OUT_QUAD,
-            duration: time,
-        });
-    }
 
-    _diffToPage(pageNumber) {
-        let currentScrollPosition = this._adjustment.value;
-        return Math.abs(currentScrollPosition - this._grid.getPageY(pageNumber));
+        // Tween the change between pages.
+        this._adjustment.ease(this._grid.getPageY(this._grid.currentPage), {
+            mode: Clutter.AnimationMode.EASE_OUT_CUBIC,
+            duration: animate ? PAGE_SWITCH_TIME : 0,
+        });
     }
 
     openSpaceForPopup(item, side, nRows) {
@@ -650,6 +628,9 @@ var AllView = GObject.registerClass({
         if (this._displayingPopup || !this._scrollView.reactive)
             return Clutter.EVENT_STOP;
 
+        if (this._swipeTracker.canHandleScrollEvent(event))
+            return Clutter.EVENT_PROPAGATE;
+
         if (!this._canScroll)
             return Clutter.EVENT_STOP;
 
@@ -673,34 +654,36 @@ var AllView = GObject.registerClass({
         return Clutter.EVENT_STOP;
     }
 
-    _onPan(action) {
-        if (this._displayingPopup)
-            return false;
-        this._panning = true;
-        this._clickAction.release();
-        let [dist_, dx_, dy] = action.get_motion_delta(0);
-        let adjustment = this._adjustment;
-        adjustment.value -= (dy / this._scrollView.height) * adjustment.page_size;
-        return false;
-    }
-
-    _onPanEnd(action) {
-        if (this._displayingPopup)
+    _swipeBegin(tracker, monitor) {
+        if (monitor !== Main.layoutManager.primaryIndex)
             return;
 
-        let pageHeight = this._grid.getPageHeight();
+        let adjustment = this._adjustment;
+        adjustment.remove_transition('value');
 
-        // Calculate the scroll value we'd be at, which is our current
-        // scroll plus any velocity the user had when they released
-        // their finger.
+        let progress = adjustment.value / adjustment.page_size;
+        let points = Array.from({ length: this._grid.nPages() }, (v, i) => i);
 
-        let velocity = -action.get_velocity(0)[2];
-        let endPanValue = this._adjustment.value + velocity;
+        tracker.confirmSwipe(this._scrollView.height,
+            points, progress, Math.round(progress));
+    }
 
-        let closestPage = Math.round(endPanValue / pageHeight);
-        this.goToPage(closestPage);
+    _swipeUpdate(tracker, progress) {
+        let adjustment = this._adjustment;
+        adjustment.value = progress * adjustment.page_size;
+    }
 
-        this._panning = false;
+    _swipeEnd(tracker, duration, endProgress) {
+        let adjustment = this._adjustment;
+        let value = endProgress * adjustment.page_size;
+
+        adjustment.ease(value, {
+            mode: Clutter.AnimationMode.EASE_OUT_CUBIC,
+            duration,
+            onComplete: () => {
+                this.goToPage(endProgress, false);
+            },
+        });
     }
 
     _onKeyPressEvent(actor, event) {