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The Gamepad specification defines a low-level interface that represents gamepad devices.
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This document was published by the Web Applications Working Group as the 29 May 2012 First Public Working Draft. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to public-webapps@w3.org (subscribe, archives) with [gamepad]
at the start of the subject header. All feedback is welcome.
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This section is non-normative.
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:
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words must, must not, required, should, should not, recommended, may, and optional in this specification are to be interpreted as described in [RFC2119].
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.
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
InterfaceThis interface defines an individual gamepad device.
interface Gamepad {
readonly attribute string id;
readonly attribute long index;
readonly attribute DOMTimeStamp timestamp;
readonly attribute float[] axes;
readonly attribute float[] buttons;
};
axes
of type array of float, readonlyid
of type string, readonlyindex
of type long, readonlyNavigator
.
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.
timestamp
of type DOMTimeStamp, readonlyaxes
and button
data
have been updated from the hardware, relative to a previously saved
timestamp.
GamepadEvent
Interfaceinterface GamepadEvent : Event {
readonly attribute Gamepad
gamepad;
};
gamepad
of type Gamepad
, readonlyThis section is non-normative.
The example below demonstrates typical access to gamepads. Note the relationship with the WindowAnimationTiming interface.
function runAnimation() { window.requestAnimationFrame(runAnimation); for (var i = 0; i < navigator.gamepads.length; ++i) { var pad = navigator.gamepads[i]; // todo; simple demo of displaying pad.axes and pad.buttons } } window.requestAnimationFrame(runAnimation);
Best Practice 1: 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.
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 will be dispatched when the user presses a button or moves an axis.
When a gamepad is disconnected from the user agent, if the user agent has previously dispatched a gamepadconnected event, a gamepaddisconnected event must be dispatched.
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.
This section is non-normative.
Many have made contributions in code, comments, or documentation:
Please let me know if I have inadvertently omitted your name.
No informative references.