Mapping device tilt to player character (etc) movement behaviour

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.

Answer 2

So, we desire to move our character - we'll call him 'loco' - based on the accelerometer's x and y data.

Now, if we do want the magnitude of the tilt to affect the rate of loco's travel, we can simply factor the accelerometer x or y value directly into our algorithm for his movement.

For example: (psuedocode)

// we'll call our accelerometer value for x 'tiltX'
// tiltX is .5; // assume that accelerometer updated the latest x value to .5
// unitOfMovement = 1; // some arbitraty increment you choose for a unit of movement

loco.x += unitOfMovement * tiltValueX;

This will cause loco to move that number of pixels for each game cycle (or whatever cycle you are driving the updates for movement by) and that here is 1 pixel multiplied by the accelerometer value. So if the character normally moves 1 pixel right at full tiltX (1.0), then if tiltX comes in from the accelerometer at .5, loco will move half that. When the value of tiltX increases, so too will the movement of Loco.

Another consideration is whether you want the movement tied directly to the rate of accelerometer events? Probably not, so you can use an array to just hold the last ten x values (same concept for y values too) sent by the accelerometer and use the latest average of the array (sum of x values / number of elements in array) at each game loop. That way, the sensitivity will feel more appropriate than driving the movement by whatever the update rate of the accelerometer may be.

Answer 3

Have a look at Point in Tilt Direction - iPhone which is first answer is very helpful I think.