Input

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Mobile Input

Unity iOS/Android offers you access to iPhone's, iPad's and Android's input systems via Input and iOS Input scripting interfaces.

Input provides access to the multi-touch screen, accelerometer and device orientation. iOS Input provides access to geographical location.

Access to keyboard on mobile devices is provided via the iOS keyboard.

Multi-Touch Screen

The iPhone and iPod Touch devices are capable of tracking up to five fingers touching the screen simultaneously. You can retrieve the status of each finger touching the screen during the last frame by accessing the Input.touches property array.

Each finger touch is represented by an Input.Touch data structure:

fingerId	The unique index for a touch.
position	The screen position of the touch.
deltaPosition	The screen position change since the last frame.
deltaTime	Amount of time that has passed since the last state change.
tapCount	The iPhone/iPad screen is able to distinguish quick finger taps by the user. This counter will let you know how many times the user has tapped the screen without moving a finger to the sides. Android devices do not count number of taps, this field is always 1.
phase	Describes so called "phase" or the state of the touch. It can help you determine if touch just began, if user moved the finger or if he just lifted the finger.

Phase can be one of the following:

Began	A finger just touched the screen.
Moved	A finger moved on the screen.
Stationary	A finger is touching the screen but hasn't moved since last frame.
Ended	A finger was lifted from the screen. This is the final phase of a touch.
Canceled	The system cancelled tracking for the touch, as when (for example) the user puts the device to her face or more than five touches happened simultaneously. This is the final phase of a touch.

Following is an example script which will shoot a ray whenever the user taps on the screen:

var particle : GameObject;
function Update () {
	for (var touch : Touch in Input.touches) {
		if (touch.phase == TouchPhase.Began) {
			// Construct a ray from the current touch coordinates
			var ray = Camera.main.ScreenPointToRay (touch.position);
			if (Physics.Raycast (ray)) {
				// Create a particle if hit
				Instantiate (particle, transform.position, transform.rotation);
			}
		}
	}
}

Mouse Simulation

On top of native touch support Unity iOS/Android provides a mouse simulation. You can use mouse functionality from the standard Input class.

Device Orientation

Unity iOS/Android allows you to get discrete description of the device physical orientation in three-dimensional space. Detecting a change in orientation can be useful if you want to create game behaviors depending on how the user is holding the device.

You can retrieve device orientation by accessing the Input.deviceOrientation property. Orientation can be one of the following:

Unknown	The orientation of the device cannot be determined. For example when device is rotate diagonally.
Portrait	The device is in portrait mode, with the device held upright and the home button at the bottom.
PortraitUpsideDown	The device is in portrait mode but upside down, with the device held upright and the home button at the top.
LandscapeLeft	The device is in landscape mode, with the device held upright and the home button on the right side.
LandscapeRight	The device is in landscape mode, with the device held upright and the home button on the left side.
FaceUp	The device is held perpendicular to the ground with the screen facing upwards.
FaceDown	The device is held perpendicular to the ground with the screen facing downwards.

Accelerometer

As the mobile device moves, a built-in accelerometer reports linear acceleration changes along the three primary axes in three-dimensional space. Acceleration along each axis is reported directly by the hardware as G-force values. A value of 1.0 represents a load of about +1g along a given axis while a value of -1.0 represents -1g. If you hold the device upright (with the home button at the bottom) in front of you, the X axis is positive along the right, the Y axis is positive directly up, and the Z axis is positive pointing toward you.

You can retrieve accelerometer value by accessing the Input.acceleration property.

Following is an example script which will move an object using accelerometer:

var speed = 10.0;
function Update () {
	var dir : Vector3 = Vector3.zero;

	// we assume that device is held parallel to the ground
	// and Home button is in the right hand

	// remap device acceleration axis to game coordinates:
	//  1) XY plane of the device is mapped onto XZ plane
	//  2) rotated 90 degrees around Y axis
	dir.x = -Input.acceleration.y;
	dir.z = Input.acceleration.x;

	// clamp acceleration vector to unit sphere
	if (dir.sqrMagnitude > 1)
		dir.Normalize();

	// Make it move 10 meters per second instead of 10 meters per frame...
	dir *= Time.deltaTime;

	// Move object
	transform.Translate (dir * speed);
}

Low-Pass Filter

Accelerometer readings can be jerky and noisy. Applying low-pass filtering on the signal allows you to smooth it and get rid of high frequency noise.

The following script shows you how to apply low-pass filtering to accelerometer readings:

var AccelerometerUpdateInterval : float = 1.0 / 60.0;
var LowPassKernelWidthInSeconds : float = 1.0;

private var LowPassFilterFactor : float = AccelerometerUpdateInterval / LowPassKernelWidthInSeconds; // tweakable
private var lowPassValue : Vector3 = Vector3.zero;
function Start () {
	lowPassValue = Input.acceleration;
}

function LowPassFilterAccelerometer() : Vector3 {
	lowPassValue = Mathf.Lerp(lowPassValue, Input.acceleration, LowPassFilterFactor);
	return lowPassValue;
}

The greater the value of LowPassKernelWidthInSeconds, the slower the filtered value will converge towards current input sample (and vice versa). You should be able to use LowPassFilter() function instead of avgSamples().

I'd like as much precision as possible when reading the accelerometer. What should I do?

Reading the Input.acceleration variable does not equal sampling the hardware. Put simply, Unity samples the hardware at a frequency of 60Hz and stores the result into the variable. In reality, things are a little bit more complicated -- accelerometer sampling doesn't occur at consistent time intervals, if under significant CPU loads. As a result, the system might report 2 samples during one frame, then 1 sample during the next frame.

You can access all measurements executed by accelerometer during the frame. The following code will illustrate a simple average of all the accelerometer events that were collected within the last frame:

var period : float = 0.0;
var acc : Vector3 = Vector3.zero;
for (var evnt : iPhoneAccelerationEvent  in iPhoneInput.accelerationEvents) {
	acc += evnt.acceleration * evnt.deltaTime;
	period += evnt.deltaTime;
}
if (period > 0)
	acc *= 1.0/period;
return acc;

Further Reading

The Unity mobile input API is originally based on Apple's API. It may help to learn more about the native API to better understand Unity's Input API. You can find the Apple input API documentation here:

• Programming Guide: Event Handling (Apple iPhone SDK documentation)
• UITouch Class Reference (Apple iOS SDK documentation)

Note: The above links reference your locally installed iPhone SDK Reference Documentation and will contain native ObjectiveC code. It is not necessary to understand these documents for using Unity on mobile devices, but may be helpful to some!

Page last updated: 2010-09-24

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