I was giving the workshop of Dorkbot_HK #4: Mobile U today afternoon at Videotage, and I have shared how to use Processing and Phonegap to create an app for iOS devices.
Here are the materials for share, the notes and the project files, BackgroundImage, and MagneticFlocking, I made as examples.

Further, I would also like to share some links which you may do the programming online / on device

Online editors (web pages) that you may do some programming.
sketch.processing
JSFIDDLE
Rendera – HTML5 online editor
GLSL Sandbox

More programming with your mobile device on road
Codea – Lua based programming to make simple games & simulation
Coders – BASIC style coding to easily create some drawings
Shaderific – prototyping and tweaking GLSL shaders

Or, you may do the design, and let an online service to do the rest for you
codiqa
viziapps

After all, happy creative coding !