I want a simple joystick-like input widget for touch devices (phones and tablets) that is effectively 5 buttons: left, right, up, down, and stop. It's the main control of a game and it let's the player direct an object around the screen. Something like this:
download bmml source – Wireframes created with Balsamiq Mockups
So what I'm looking for are established conventions for this kind of control on a touch screen, if there are any.