API for adjusting step duration (gate length)

libs/ardour/ardour/step_sequencer.h

@@ -59,6 +59,7 @@ class Step : public PBD::Stateful {
 
 	void adjust_velocity (int amt);
 	void adjust_pitch (int amt);
+	void adjust_duration (double amt);
 	void adjust_octave (int amt);
 
 	Mode mode() const { return _mode; }

libs/ardour/step_sequencer.cc

@@ -104,6 +104,23 @@ Step::set_enabled (bool yn)
 	_enabled = yn;
 }
 
+void
+Step::adjust_duration (double amt)
+{
+	const double new_dur = _duration + amt;
+
+	if (new_dur > 1.0) {
+		_duration = 1.0;
+	} else if (new_dur < 1.0/64.0) {
+		_duration = 0.0;
+	} else {
+		_duration = new_dur;
+	}
+
+	PropertyChange pc;
+	PropertyChanged (pc);
+}
+
 void
 Step::adjust_pitch (int amt)
 {