Question

The context is an iPad game in which I want an on-screen object to be controlled by X/Y tilt of the device.

I was wondering if anybody can point me in the direction of resources for deciding on an appropriate mapping of tilt to the movement behaviour (e.g. whether people tend to use the “raw” rotation values to control the acceleration, velocity or direct position, and how comfortable players have been found to be with these different types of ‘mapping’ of device rotation to object movement).

I appreciate that the appropriate choice can depend on the particular type of game/object being controlled, and that some trial and error will be needed, but I wondered as a starting point at least what existing knowledge there was to draw on.

Answer 1

First you’re going to want to apply a low-pass filter to isolate tilt from noise and your user’s shaky hands, Apple shows this in their accelerometer examples

x = accel.x * alpha + x * (1.0 - alpha);
y = accel.y * alpha + y * (1.0 - alpha);

more alpha causes more responsiveness at the cost of more noisy input.

Unless your game is intentionally simulating a ball balancing on the face of the screen, you probably don’t want to apply your tilt values to acceleration, but rather to target velocity or target position, applying "fake" smooth acceleration to get it there.

Also, this answer has a neat idea if Unity3d is acceptable for your project, and this paper has some handy numbers on the practical limits of using tilt control as input, including making the important point that users have a much easier time controlling absolute angle position than velocity of tilt.