ripples: Add a new class ripples

So we can use the same code for both the ripples in overview and the
pointer location.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/981
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/413
https://gitlab.gnome.org/GNOME/mutter/merge_requests/453
https://gitlab.gnome.org/GNOME/gsettings-desktop-schemas/merge_requests/19
https://gitlab.gnome.org/GNOME/gnome-settings-daemon/merge_requests/86

js/js-resources.gresource.xml

@@ -84,6 +84,7 @@
     <file>ui/pointerWatcher.js</file>
     <file>ui/popupMenu.js</file>
     <file>ui/remoteSearch.js</file>
+    <file>ui/ripples.js</file>
     <file>ui/runDialog.js</file>
     <file>ui/screenShield.js</file>
     <file>ui/screencast.js</file>

js/ui/ripples.js

@@ -0,0 +1,97 @@
+// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+
+const { Clutter, St } = imports.gi;
+const Tweener = imports.ui.tweener;
+
+// Shamelessly copied from the layout "hotcorner" ripples implementation
+var Ripples = class Ripples {
+    constructor(px, py, styleClass) {
+        this._x = 0;
+        this._y = 0;
+
+        this._px = px;
+        this._py = py;
+
+        this._ripple1 = new St.BoxLayout({ style_class: styleClass,
+                                           opacity: 0,
+                                           can_focus: false,
+                                           reactive: false,
+                                           visible: false });
+        this._ripple1.set_pivot_point(px, py);
+
+        this._ripple2 = new St.BoxLayout({ style_class: styleClass,
+                                           opacity: 0,
+                                           can_focus: false,
+                                           reactive: false,
+                                           visible: false });
+        this._ripple2.set_pivot_point(px, py);
+
+        this._ripple3 = new St.BoxLayout({ style_class: styleClass,
+                                           opacity: 0,
+                                           can_focus: false,
+                                           reactive: false,
+                                           visible: false });
+        this._ripple3.set_pivot_point(px, py);
+    }
+
+    _animRipple(ripple, delay, time, startScale, startOpacity, finalScale) {
+        // We draw a ripple by using a source image and animating it scaling
+        // outwards and fading away. We want the ripples to move linearly
+        // or it looks unrealistic, but if the opacity of the ripple goes
+        // linearly to zero it fades away too quickly, so we use Tweener's
+        // 'onUpdate' to give a non-linear curve to the fade-away and make
+        // it more visible in the middle section.
+
+        ripple.x = this._x;
+        ripple.y = this._y;
+        ripple._opacity = startOpacity;
+        ripple.visible = true;
+        ripple.opacity = 255 * Math.sqrt(startOpacity);
+        ripple.scale_x = ripple.scale_y = startScale;
+        ripple.set_translation( - this._px * ripple.width, - this._py * ripple.height, 0.0);
+
+        Tweener.addTween(ripple, { _opacity: 0,
+                                   scale_x: finalScale,
+                                   scale_y: finalScale,
+                                   delay: delay,
+                                   time: time,
+                                   transition: 'linear',
+                                   onUpdate() { ripple.opacity = 255 * Math.sqrt(ripple._opacity); },
+                                   onComplete() { ripple.visible = false; } });
+    }
+
+    addTo(stage) {
+        if (this._stage !== undefined) {
+            throw new Error('Ripples already added');
+            return;
+        }
+
+        this._stage = stage;
+        this._stage.add_actor(this._ripple1);
+        this._stage.add_actor(this._ripple2);
+        this._stage.add_actor(this._ripple3);
+    }
+
+    playAnimation(x, y) {
+        if (this._stage === undefined) {
+            throw new Error('Ripples not added');
+            return;
+        }
+
+        this._x = x;
+        this._y = y;
+
+        this._stage.set_child_above_sibling(this._ripple1, null);
+        this._stage.set_child_above_sibling(this._ripple2, this._ripple1);
+        this._stage.set_child_above_sibling(this._ripple3, this._ripple2);
+
+        // Show three concentric ripples expanding outwards; the exact
+        // parameters were found by trial and error, so don't look
+        // for them to make perfect sense mathematically
+
+        //                              delay  time  scale opacity => scale
+        this._animRipple(this._ripple1, 0.0,   0.83,  0.25,  1.0,     1.5);
+        this._animRipple(this._ripple2, 0.05,  1.0,   0.0,   0.7,     1.25);
+        this._animRipple(this._ripple3, 0.35,  1.0,   0.0,   0.3,     1);
+    }
+};