DRAFT Web Events Working Group Charter

Scope

As increasingly advanced webapps are developed, the need to address input by a variety of user-interface modes and devices becomes more important.

Touch Interfaces

Web browsers and mobile devices are making increasing use of touch-sensitive inputs, such as with a screen, trackpad, or tablet interface, as the primary or supplementary interface for web applications. This enables web developers to build more intuitive and sophisticated applications that fit naturally with the device being used. Touch interfaces have a long history going back to the 1960s, and faster, less expensive hardware and recent deployment on mobile devices have led to a proliferation of different approaches to software interface design. Touch interfaces frequently make use of custom gestures to signal user intent.

A related class of devices, including drawing tablets, interactive surfaces, pen devices, digital whiteboards, and spatial sensors, are also becoming more Web-enabled, driving the need to account for a wider range of capability than simple touch interfaces.

The aim of this group is to determine an appropriate set of functionality to standardize, and to define those features in way that may be deployed quickly, widely, and interoperably.

Touch events are simple, but may have characteristics different than mouse events, including pressure sensitivity. Pen tablets may add hovering and modal aspects to touch events. Multitouch events add yet another layer, allowing a user to use two or more fingers to accomplish a task, and may even permit multiple users to manipulate the user interface using the same input device, such as a screen input.

In addition to low-level direct input methods, the concept of representational events has emerged as a higher-level abstraction which may allow for device-independent inputs that map to touch inputs as well as more traditional mouse and keyboard inputs, allowing authors to express more intentionality and universal functionality. Authoring to such a wide variety of input devices, including various touch and pen-tablet devices, the traditional mouse and keyboard, as well as accessibility input devices, can be challenging; thus, a high-level set of abstracted events is useful in defining device-independent and user-interface-independent interactions. The may include task-specific events such as common editing commands.

There are four conceptual layers for touch and pen-tablet interactions: physical; gestural; representational; and intentional.

• physical: This is lowest level, and deals with the physical actions that a user takes when interacting with a device, such as placing one or more fingers on a screen and moving them, applying varying pressure on a tablet with a pen, or pressing a physical button.
• gestural: This is a middle layer between the physical and intentional, and describes specific mappings between the two; for example, a "pinch" gesture may represent the user placing two fingers on a screen and moving them together at the physical layer, and this may map to a 'zoom-in' event at the intentional layer. However, these gestures are normally specific to particular devices and platforms, and may not be suitable for standardization yet. Experimentation with different implementations and script libraries may yield more concrete goals for specific gesture events in the future.
• representational: This is the highest level of abstraction in the event model, and indicates the means by which the user is performing a task, such as zooming in, panning, navigating to the next page, activating a control, and so on.
• intentional: This is a level beyond the API itself, and indicates the action the user is trying to accomplish, such as viewing more or less detail (zooming in and out), viewing another part of the larger picture (panning), and so forth.

Finally, different devices may have associated metadata beyond the physical layer, such as modal information which should be available to content developers; for example, a tablet device may have multiple pens with different colors or brush styles associated with each. A method for the device to convey this to the application along with other event information is very desirable, and a generic metadata property should be defined to facilitate this in an extensible way that will allow for novel future device inputs.

The Web Events Working Group's deliverables include documenting appropriate use-cases and requirements, and a specification for events and APIs to enable low-level physical events and high-level representational events, which may describe some mapping between the two; for ease and clarity of authoring, the model should include a way to manage the complex relationship between mouse and low-level multi-touch events, and should include a generic metadata property for device-specific non-physical modalities.

Mouse Lock

Traditional pointer-device interaction involves moving the cursor on screen in response to user manipulation of the input device (e.g. moving the mouse). However, another common mode for mouse interaction, especially in gaming, is to use the mouse to change the viewport itself, rather than a cursor. This is an essential input mode for certain classes of applications, especially first-person-perspective 3D applications and 3D modeling software. The Mouse Lock API deliverable defines an API that provides scripted access to raw mouse movement data while locking the target of mouse events to a single element and removing the cursor from view.

This is a new deliverable, the Mouse Lock API.

Game Controllers

Some user agents have connected gamepad devices (also known as joysticks), which can be used for games and other "10-foot" user interfaces (e.g. presentations, media viewers). Currently, the only way for a gamepad to be used as input for webapps is to emulate mouse or keyboard events; however, information is lost with this approach, and it requires additional emulation software outside of the user agent. This deliverable defines support for devices common to current gaming systems including gamepads, directional pads, joysticks, wheels, pedals, accelerometers.

This is a new deliverable, the Gamepad API.

Guidelines

The Working Group also intends to include guidelines for providing alternative interaction methods for people with disabilities—specifically those disabilities involving motor skills and vision; these guidelines should include both traditional interaction methods such as mouse/keyboard, game controllers, and interaction methods based on tactile feedback systems for touchscreens. These deliverables must apply to desktop and mobile browsers, and other non-browser environments where appropriate, and must be consistent with Web technologies designed in other working groups including WebApps, DAP, HTML, and SVG.

Out of Scope

In order to get the broadest possible participation and quickest standardization of the physical and representational events that are currently missing from the Web platform, the normative definition of specific gesture events are out of scope for the Web Events Working Group at this time. A future charter may include normative gesture events as a deliverable, based on implementation and development experience.

Pen/stylus-tablet interactions have many different aspects; ink and handwriting APIs are related topics, but are outside the scope of this current charter. For digital ink representation, see the InkML specification.

There are many types of game controller, but the gamepad deliverable will deal only with traditional joysticks and button-based controllers with accelerometers, and excludes support for more complex devices that do camera-based motion sensing, depth sensing, video analysis, and gesture recognition.

Success Criteria

In order to advance to Proposed Recommendation, each specification is expected to have at least two independent implementations of each of feature defined in the specification.