@Override
	protected final void addToCenter(
			final DropTarget<JPanel, JPanel, JPanel> target) {
		final Container c = (Container) ((Container) this.center
				.getComponent(0)).getComponent(0);
		if (this.empty != null) {
			this.empty = null;
			c.removeAll();
			c.setBackground(this.emptyC);
		}
		final Set<Integer> tracks = new HashSet<>();
		for (final DragObject<JPanel, JPanel, JPanel> o : target) {
			tracks.add(o.getId());
		}
		this.instrumentToTrack.put((MidiInstrumentDropTarget) target, tracks);
		c.removeAll();
		for (final MidiInstrumentDropTarget t : this.instrumentToTrack.keySet()) {
			c.add(t.getDisplayableComponent());
		}
		this.center.revalidate();
	}