Follow-up to a6ece30: allow changing volume anywhere with ALT key.

The master volume can now be changed (using the mouse wheel) with the ALT key pressed in any menu, as in osu!.

Also improved the handling of dimmed tracks.

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/states/OptionsMenu.java

@@ -342,6 +342,12 @@ public class OptionsMenu extends BasicGameState {
 			option.drag(container, diff);
 	}
 
+	@Override
+	public void mouseWheelMoved(int newValue) {
+		if (input.isKeyDown(Input.KEY_LALT) || input.isKeyDown(Input.KEY_RALT))
+			UI.changeVolume((newValue < 0) ? -1 : 1);
+	}
+
 	@Override
 	public void keyPressed(int key, char c) {
 		// key entry state