Now this is most simple way to control any software from ipad or iphone. Using Astropad app for ipad and mac you can control all your desktop space from ipad. You can also scale any part of screen, so it is useful for VJs. As you can see there are some artefacts and glitches in app, but it does not affect to performance. App work responsive, I tested it on ipad air and macbook retina 2013.
Astropad works wirelessly or over USB. Astropad created for designers and it supports stilus tools. You can find it at astropad.com