NOTE: Layouts are an advanced, mostly internal feature of the input system. It is not necessary to understand this feature to use the input system. Knowledge of the layout system is mostly useful when wanting to support custom devices or when wanting to modify the behavior of existing devices.

Layouts

A layout describes a memory format and the controls to build in order to read and write data to/from memory in the given format.

Layouts are the central mechanism by which the input system learns about types of input devices and input controls. Each layout represents a specific composition of input controls. By matching the description of a device to a layout, the input system is able to create the correct type of device and interpret the incoming input data correctly.

The input system ships with a big set of layouts for common control types, as well as for common devices. For other device types, layouts are automatically generated on the fly based on the device description reported by the device's interface.

The set of currently understood layouts can be browsed from the input debugger.

A layout has two primary functions:

• Describe a certain memory layout containing input data.
• Assign names, structure, and meaning to the controls operating on the data.

A layout can either be for a control on a device (e.g. Stick) or for a device itself (i.e. something based on InputDevice).

Layouts are only loaded when needed -- usually when creating a new device. A layout can be manually loaded through InputSystem.LoadLayout. This returns an InputControlLayout instance containing the fully merged (i.e. containing any information inherited from based layouts and/or affected by layout overrides), final structure of the layout.

New layouts can be registered through InputSystem.RegisterLayout.

Layout Formats

New layouts can be added in one of three ways.

1. Represented by C# structs and classes.
2. In JSON format.
3. Built-on the fly at runtime using what's called "layout builders".

Layout from Type

In its most basic form, a layout can simply be a C# class (derived from InputControl for a control layout or derived from InputDevice for a device layout).

// The InputControlLayout attribute is not strictly necessary here.
// However, it can be used to set additional properties (such as
// a custom display name for the layout).
[InputControlLayout]
public class MyDevice : InputDevice
{
    public AxisControl axis { get; private set; }
    public ButtonControl button { get; private set; }

    protected override void FinishSetup(InputDeviceBuilder builder)
    {
        base.FinishSetup(builder);

        axis = builder.GetControl<AxisControl>("axis");
        button = builder.GetControl<ButtonControl>("button");
    }
}

The layout can be registered with InputSystem.RegisterLayout. This works the same for control and for device layouts.

// NOTE: This should generally be done from InitializeOnLoad/
// RuntimeInitializeOnLoad code.
InputSystem.RegisterLayout<MyDevice>();

When the layout is instantiated, the system will look at every field and property defined directly in the type to potentially turn it into one or more control items.

1. If the field or property is annotated with InputControlAttribute, the attribute's properties will be applied to the control item. Some special defaults apply in this case:
   • If no offset is set and the attribute is applied to a field, offset defaults to the offset of the field.
   • If no name is set, it defaults to the name of the property/field.
   • If no layout is set, it is inferred from the type of the field/property.
2. If the field or property has a struct type which implements IInputStateTypeInfo, the field is considered to be an embedded state struct and the field/property will be recursed into to gather controls from it.
3. Otherwise, if the type of the field or property is based on InputControl, a control item will be added similar to case 1) when the member is annotated with InputControlAttribute.

Using a State Structure

When implementing support for a new input device, there usually is an existing data format in which input for the device is received. The easiest way to add support for the given data format is to describe it with a C# struct annotated with InputControlAttribute.

public struct MyDeviceState : IInputStateTypeInfo
{
    public FourCC format => new FourCC('M', 'D', 'E', 'V');

    [InputControl(name = "button1", layout = "Button", bit = 0)]
    [InputControl(name = "button2", layout = "Button", bit = 1)]
    [InputControl(name = "dpad", layout = "Dpad", bit = 2, sizeInBits = 4)]
    [InputControl(name = "dpad/up", bit = 2)]
    [InputControl(name = "dpad/down", bit = 3)]
    [InputControl(name = "dpad/left", bit = 4)]
    [InputControl(name = "dpad/right", bit = 5)]
    public int buttons;

    [InputControl(layout = "Stick")]
    public Vector2 stick;

    [InputControl(layout = "Axis")] // Automatically converts from byte to float.
    public byte trigger;
}

// The device must be directed to the state struct we have created.
[InputControlLayout(stateType = typeof(MyDeviceState)]
public class MyDevice : InputDevice
{
}

Layout from JSON

You can also create a layout from a JSON string containing the same information. This is mostly useful if you want to be able to store/transfer layout information separate from your code - for instance if you want to be able to add support for new devices dynamically without making a new build of your game. You can use InputControlLayout.ToJson() and InputControlLayout.FromJson() to convert layouts to and from the format.

The same layout as above looks like this in JSON format:

{
    "name": "MyDevice",
    "format": "MDEV",
    "controls": [
        {
            "name": "button1",
            "layout": "Button",
            "offset": 0,
            "bit": 0,
        },
        {
            "name": "button2",
            "layout": "Button",
            "offset": 0,
            "bit": 1,
        },
        {
            "name": "dpad",
            "layout": "Dpad",
            "offset": 0,
            "bit": 2,
            "sizeInBits": 4,
        },
        {
            "name": "dpad/up",
            "offset": -1,
            "bit": 2,
        },
        {
            "name": "dpad/down",
            "offset": -1,
            "bit": 3,
        },
        {
            "name": "dpad/left",
            "offset": -1,
            "bit": 4,
        },
        {
            "name": "dpad/right",
            "offset": -1,
            "bit": 5,
        },
        {
            "name": "stick",
            "layout": "Stick",
            "offset": 4,
            "format": "VEC2",
        },
        {
            "name": "trigger",
            "layout": "Axis",
            "offset": 12,
            "format": "BYTE",

        }
    ]
}

Layout Builders

Finally, layouts can also be built on the fly in code. This is useful for device interfaces such as HID that supply descriptive information for each device.

To build layouts dynamically in code, you can use the InputControlLayout.Builder API.

Here's the same layout from the previous examples constructed programmatically:

var builder = new InputControlLayout.Builder()
    .WithName("MyDevice")
    .WithFormat("MDEV");

builder.AddControl("button1")
    .WithLayout("Button")
    .WithByteOffset(0)
    .WithBitOffset(0);

builder.AddControl("button2")
    .WithLayout("Button")
    .WithByteOffset(0)
    .WithBitOffset(1);

builder.AddControl("dpad")
    .WithLayout("Dpad")
    .WithByteOffset(0)
    .WithBitOffset(2)
    .WithSizeInBits(4);

builder.AddControl("dpad/up")
    .WithByteOffset(-1)
    .WithBitOffset(2);

builder.AddControl("dpad/down")
    .WithByteOffset(-1)
    .WithBitOffset(3);

builder.AddControl("dpad/left")
    .WithByteOffset(-1)
    .WithBitOffset(4);

builder.AddControl("dpad/right")
    .WithByteOffset(-1)
    .WithBitOffset(5);

builder.AddControl("stick")
    .WithLayout("Stick")
    .WithByteOffset(4)
    .WithFormat("VEC2");

builder.AddControl("trigger")
    .WithLayout("Axis")
    .WithByteOffset(12)
    .WithFormat("BYTE");

var layout = builder.Build();

Layout Inheritance

A layout can be derived from an existing layout. This process is based on a simple process of merging the information from a derived layout on top of the information present in the derived layout.

• For layouts defined as types, the base layout is the layout of the base type (if any).
• For layouts defined in JSON, the base layout can be specified in the extends property of the root node.
• For layouts created in code using InputControlLayout.Builder, you can specify a base layout using InputControlLayout.Builder.Extend().

Control Items

Each layout is comprised of zero or more control items. Each item either describes a new control or modifies the properties of an existing control. The latter can also reach down into the hierarchy and modify properties of a control added implicitly as a child by another item.

    // Add a dpad control.
    [InputControl(layout = "Dpad")]
    // And now modify the properties of the "up" control that was added by the
    // "Dpad" layout above.
    [InputControl(name = "dpad/up", displayName = "DPADUP")]
    public int buttons;

The following table details the properties that a control item can have. These can be set either as properties on InputControlAttribute, as properties on the control in JSON, or through methods on InputControlLayout.Builder.ControlBuilder.

Property	Description
name	Name of the control. Defaults to the name of the field/property that InputControlAttribute is applied to.
displayName	Display name of the control (for use in UI strings).
shortDisplayName	Short display name of the control (for use in UI strings).
layout	Layout to use for the control.
variants	Variants of the control.
aliases	Aliases for the control. These are alternative names the control can be referred to.
usages	Usages of the control.
offset	The byte offset at which the state for the control is found.
bit	The bit offset at which the state for the control is found within it's byte.
sizeInBits	The total size of the control's state, in bits.
arraySize	If this is set to a non-zero value, will create an array of controls of this size.
parameters	Any parameters to be passed to the control. These will be applied to any fields the control type may have, such as AxisControl.scaleFactor.
processors	Processors to apply to the control.
noisy	Whether the control is to be considered noisy.
synthetic	Whether the control is to be considered synthetic.
defaultState	What value to initialize the state memory for the control to by default.
useStateFrom	For synthetic controls, used to synthesize control state.
minValue	The minimum value the control can report. Used for evaluating control magnitude.
maxValue	The maximum value the control can report. Used for evaluating control magnitude.

Layout Overrides

It is possible to non-destructively alter aspects of an existing layout using what's called "layout overrides". You can call InputSystem.RegisterLayoutOverride to register a layout as an override of it's base layout. Any property present in the override will then be added to the base layout (or override existing properties).

// Add an extra control to the "Mouse" layout
const string json = @"
    {
        ""name"" : ""Overrides"",
        ""extend"" : ""Mouse"",
        ""controls"" : [
            { ""name"" : ""extraControl"", ""layout"" : ""Button"" }
        ]
    }
";

InputSystem.RegisterLayoutOverride(json);