The Gamepad specification defines a low-level interface that represents gamepad devices.
If you have comments for this spec, please send them to public-webapps@w3.org with a Subject: prefix of [gamepad]. See Bugzilla for this specification's open bugs.

Introduction

Some user agents have connected gamepad devices. These devices are desirable and suited to input for gaming applications, and for "10 foot" user interfaces (presentations, media viewers).

Currently, the only way for a gamepad to be used as input would be to emulate mouse or keyboard events, however this would lose information and require additional software outside of the user agent to accomplish emulation.

Meanwhile, native applications are capable of accessing these devices via system APIs.

The Gamepad API provides a solution to this problem by specifying interfaces that allow web applications to directly act on gamepad data.

This specification references interfaces from a number of other specifications:

This specification defines conformance criteria that apply to a single product: the user agent that implements the interfaces that it contains.

Implementations that use ECMAScript to implement the APIs defined in this specification MUST implement them in a manner consistent with the ECMAScript Bindings defined in the Web IDL specification [[!WEBIDL]] as this specification uses that specification and terminology.

A conforming implementation is required to implement all fields defined in this specification.

Scope

Interfacing with external devices designed to control games has the potential to become large and intractable if approached in full generality. In this specification we explicitly choose to narrow scope to provide a useful subset of functionality that can be widely implemented and broadly useful.

Specifically, we choose to only support the functionality required to support gamepads. Support for gamepads requires two input types: buttons and axes. Both buttons and axes are reported as analog values, buttons ranging from [0..1], and axes ranging from [-1..1].

While the primary goal is support for gamepad devices, supporting these two types of analog inputs allows support for other similar devices common to current gaming systems including joysticks, driving wheels, pedals, and accelerometers. As such, the name "gamepad" is exemplary rather than trying to be a generic name for the entire set of devices addressed by this specification.

We specifically exclude support for more complex devices that may also be used in some gaming contexts, including those that that do motion sensing, depth sensing, video analysis, gesture recognition, and so on.

Gamepad Interface

This interface defines an individual gamepad device.

readonly attribute DOMString id
An identification string for the gamepad. This string identifies the brand or style of connected gamepad device. Typically, this will include the USB vendor and a product ID.
readonly attribute long index
The index of the gamepad in the Navigator. When multiple gamepads are connected to a user agent, indices MUST be assigned on a first-come, first-serve basis, starting at zero. If a gamepad is disconnected, previously assigned indices MUST NOT be reassigned to gamepads that continue to be connected. However, if a gamepad is disconnected, and subsequently the same or a different gamepad is then connected, index entries MUST be reused.
readonly attribute boolean connected
Indicates whether the physical device represented by this object is still connected to the system. When a gamepad becomes unavailable, whether by being physically disconnected, powered off or otherwise unusable, the connected attribute MUST be set to false.
readonly attribute DOMHighResTimeStamp timestamp
Last time the data for this gamepad was updated. Timestamp is a monotonically increasing value that allows the author to determine if the axes and button data have been updated from the hardware. The value must be relative to the navigationStart attribute of the PerformanceTiming interface. Since values are monotonically increasing they can be compared to determine the ordering of updates, as newer values will always be greater than or equal to older values. If no data has been received from the hardware, the value of the timestamp attribute should be the time relative to navigationStart when the Gamepad object was first made available to script.
readonly attribute DOMString mapping
The mapping in use for this device. If the user agent has knowledge of the layout of the device, then it SHOULD indicate that a mapping is in use by setting this property to a known mapping name. Currently the only known mapping is "standard", which corresponds to the Standard Gamepad layout. If the user agent does not have knowledge of the device layout and is simply providing the controls as represented by the driver in use, then it MUST set the mapping property to an empty string.
readonly attribute double[] axes
Array of values for all axes of the gamepad. All axis values MUST be linearly normalized to the range [-1.0 .. 1.0]. As appropriate, -1.0 SHOULD correspond to "up" or "left", and 1.0 SHOULD correspond to "down" or "right". Axes that are drawn from a 2D input device SHOULD appear next to each other in the axes array, X then Y. It is RECOMMENDED that axes appear in decreasing order of importance, such that element 0 and 1 typically represent the X and Y axis of a directional stick.
readonly attribute GamepadButton[] buttons
Array of button states for all buttons of the gamepad. It is RECOMMENDED that buttons appear in decreasing importance such that the primary button, secondary button, tertiary button, and so on appear as elements 0, 1, 2, ... in the buttons array.

GamepadButton Interface

This interface defines the state of an individual button on a gamepad device.

readonly attribute boolean pressed
The pressed state of the button. This property MUST be true if the button is currently pressed, and false if it is not pressed. For buttons which do not have a digital switch to indicate a pure pressed or released state, the user agent MUST choose a threshold value to indicate the button as pressed when its value is above a certain amount. If the platform API gives a recommended value, the user agent SHOULD use that. In other cases, the user agent SHOULD choose some other reasonable value.
readonly attribute double value
For buttons that have an analog sensor, this property MUST represent the amount which the button has been pressed. All button values MUST be linearly normalized to the range [0.0 .. 1.0]. 0.0 MUST mean fully unpressed, and 1.0 MUST mean fully pressed. For buttons without an analog sensor, only the values 0.0 and 1.0 for fully unpressed and fully pressed MUST be provided.

Navigator Interface extension

This partial interface defines an extension to the Navigator interface.

Gamepad[] getGamepads()
Retrieve a snapshot of the data for the the currently connected and interacted-with gamepads. Gamepads MUST only appear in the list if they are currently connected to the user agent, and at least one device has been interacted with by the user. If no devices have been interacted with, devices MUST NOT appear in the list to avoid a malicious page from fingerprinting the user.

GamepadEvent Interface

readonly attribute Gamepad gamepad
The single gamepad attribute provides access to the associated gamepad data for this event.
Gamepad gamepad
The gamepad associated with this event.

Remapping

Each device manufacturer creates many different products and each has unique styles and layouts of buttons and axes. It is intended that the user agent support as many of these as possible.

Additionally there are de facto standard layouts that have been made popular by game consoles. When the user agent recognizes the attached device, it is RECOMMENDED that it be remapped to a canonical ordering when possible. Devices that are not recognized should still be exposed in their raw form.

There is currently one canonical device, the "Standard Gamepad". The standard gamepad has 4 axes, and up to 17 buttons. When remapping, the indices in axes[] and buttons[] should correspond as closely as possible to the physical locations in the diagram below. Additionally, the mapping property of the Gamepad SHOULD be set to the string "standard".

Usage Examples

The example below demonstrates typical access to gamepads. Note the relationship with the WindowAnimationTiming interface.


function runAnimation()
{
    window.requestAnimationFrame(runAnimation);

    var gamepads = navigator.getGamepads();

    for (var i = 0; i < gamepads.length; ++i)
    {
        var pad = gamepads[i];
        // todo; simple demo of displaying pad.axes and pad.buttons
    }
}

window.requestAnimationFrame(runAnimation);

              

Coordination with WindowAnimationTiming

Interactive applications will typically be using the WindowAnimationTiming interface to drive animation, and will want coordinate animation with user gamepad input. As such, the gamepad data should be polled as closely as possible to immediately before the animation callbacks are executed, and with frequency matching that of the animation. That is, if the animation callbacks are running at 60Hz, the gamepad inputs should also be sampled at that rate.

The gamepadconnected event

User agents implementing this specification must provide a new DOM event, named gamepadconnected. The corresponding event MUST be of type GamepadEvent and MUST fire on the window object. Registration for and firing of the gamepadconnected event MUST follow the usual behavior of DOM4 Events. [[!DOM4]]

A user agent MUST dispatch this event type to indicate the user has connected a gamepad. If a gamepad was already connected when the page was loaded, the gamepadconnected event SHOULD be dispatched when the user presses a button or moves an axis.

The gamepaddisconnected event

User agents implementing this specification must provide a new DOM event, named gamepaddisconnected. The corresponding event MUST be of type GamepadEvent and MUST fire on the window object. Registration for and firing of the gamepaddisconnected event MUST follow the usual behavior of DOM4 Events. [[!DOM4]]

When a gamepad is disconnected from the user agent, if the user agent has previously dispatched a gamepadconnected event for that gamepad to a window, a gamepaddisconnected event MUST be dispatched to that same window.

Other events

More discussion needed, on whether to include or exclude axis and button changed events, and whether to roll them more together (gamepadchanged?), separate somewhat (gamepadaxischanged?), or separate by individual axis and button.

Acknowledgements

Many have made contributions in code, comments, or documentation:

Please let me know if I have inadvertently omitted your name.