slider: Emit a 'drag-begin' signal when starting to drag

We are already emitting a 'drag-end' signal when no more dragging
is happening, so it makes sense to emit a 'drag-begin' too when
starting, so that apps interested in implementing different logic
between those two events can easily do it without needing to deal
with the underlying 'button-press-event' signal for the actor.

https://bugzilla.gnome.org/show_bug.cgi?id=761208

diff --git a/js/ui/slider.js b/js/ui/slider.js
index d7ae2f2feed77052877b8c84ed886379006bc917..02dbfae79852e68e46b03b515b5e71f71fa970fe 100644 (file)
--- a/js/ui/slider.js
+++ b/js/ui/slider.js
@@ -137,6 +137,10 @@ const Slider = new Lang.Class({
             this._motionId = this.actor.connect('motion-event', Lang.bind(this, this._motionEvent));
         }
 
+        // We need to emit 'drag-begin' before moving the handle to make
+        // sure that no 'value-changed' signal is emitted before this one.
+        this.emit('drag-begin');
+
         let absX, absY;
         [absX, absY] = event.get_coords();
         this._moveHandle(absX, absY);
@@ -224,6 +228,7 @@ const Slider = new Lang.Class({
             let delta = key == Clutter.KEY_Right ? 0.1 : -0.1;
             this._value = Math.max(0, Math.min(this._value + delta, 1));
             this.actor.queue_repaint();
+            this.emit('drag-begin');
             this.emit('value-changed', this._value);
             this.emit('drag-end');
             return Clutter.EVENT_STOP;