touchevents.html
author Matt Brubeck <mbrubeck@mozilla.com>
Mon, 06 Jun 2011 17:48:21 -0700
changeset 95 80bd73a2e5b2
parent 94 53491ff3514b
child 96 457c2df41b66
permissions -rw-r--r--
preventDefault recommendations for touchstart/touchmove and scrolling.
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    <title>Touch Events Specification</title>
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  <body>
    <section id='abstract'>
      The Touch Interface specification defines a set of low-level events that
      represent one or more points of contact with a touch-sensitive surface,
      and changes of those points with respect to the surface and any DOM
      elements displayed upon it (e.g. for touch screens) or associated with it
      (e.g. for drawing tablets without displays).  It also addresses
      pen-tablet devices, such as drawing tablets, with consideration toward
      stylus capabilities.
    </section>

    <section id='introduction' class='informative'>
      <h2>Introduction</h2>

      <p>
        User Agents that run on terminals which provide touch input to use web
        applications typically use interpreted mouse events to allow users
        to access interactive web applications. However, these interpreted
        events, being normalized data based on the physical touch input, tend
        to have limitations on delivering the intended user experience.
        Additionally, it is not possible to handle concurrent input regardless
        of device capability, due to constraints of mouse events: both
        system level limitations and legacy compatibility.
      </p>

      <p>
        Meanwhile, native applications are capable of handling both cases with
        the provided system APIs.
      </p>

      <p>
        The Touch Events specification provides a solution to this problem by
        specifying interfaces to allow web applications to directly handle touch
        events, and multiple touch points for capable devices.
      </p>
    </section>

    <section id='conformance'>
      <p>
        This specification defines conformance criteria that apply to a single
        product: the <dfn id="dfn-user-agent">user agent</dfn> that implements
        the interfaces that it contains.
      </p>

      <p>
        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.
      </p>

      <p>
        A conforming implementation is required to implement all fields
        defined in this specification.
      </p>
    </section>

    <section>
      <h2><a>Touch</a> Interface</h2>
      <p>
        This interface defines an individual point of contact for a touch
        event.
      </p>

      <dl title='interface Touch' class='idl'>
        <dt>readonly attribute long identifier</dt>
        <dd>
          An identification number for each <a>touch point</a>.

          When a touch point becomes active, it must be assigned an
          <a>identifier</a> that is distinct from any other <a>active touch
          point</a>.  While the touch point remains active, all events that
          refer to it must assign it the same <a>identifier</a>.
        </dd>

        <dt>readonly attribute long screenX</dt>
        <dd>
          x-coordinate of point relative to the screen
        </dd>
        <dt>readonly attribute long screenY</dt>
        <dd>
          y-coordinate of point relative to the screen
        </dd>

        <dt>readonly attribute long clientX</dt>
        <dd>
          x-coordinate of point relative to the viewport, excluding any scroll
          offset
        </dd>
        <dt>readonly attribute long clientY</dt>
        <dd>
          y-coordinate of point relative to the viewport, excluding any scroll
          offset
        </dd>

        <dt>readonly attribute long pageX</dt>
        <dd>
          x-coordinate of point relative to the viewport, including any scroll
          offset
        </dd>
        <dt>readonly attribute long pageY</dt>
        <dd>
          y-coordinate of point relative to the viewport, including any scroll
          offset
        </dd>

        <dt>readonly attribute long radiusX</dt>
        <dd>
          the radius of the ellipse which most closely circumscribes the
          touching area (e.g. finger, stylus) along the x-axis, in pixels of
          the same scale as <a>screenX</a>; <code>1</code> if no value is
          known.  The value must be positive.
          <p class="issue" id="issue-units"><strong>Issue:</strong> What are
          units of radiusX/radiusY?  CSS Pixels?</p>
        </dd>
        <dt>readonly attribute long radiusY</dt>
        <dd>
          the radius of the ellipse which most closely circumscribes the
          touching area (e.g. finger, stylus) along the y-axis, in pixels of
          the same scale as <a>screenY</a>; <code>1</code> if no value is
          known.  The value must be positive.
        </dd>

        <dt>readonly attribute float rotationAngle</dt>
        <dd>
          <p>
            the angle (in degrees) that the ellipse described by <a>radiusX</a>
            and <a>radiusY</a> is rotated clockwise about its center;
            <code>0</code> if no value is known.  The value must be greater
            than or equal to <code>0</code> and less than <code>90</code>.
          </p>
          <p>
            If the ellipse described by <a>radiusX</a> and <a>radiusY</a> is
            circular, then <a>rotationAngle</a> has no effect.  The user agent
            may use <code>0</code> as the value in this case, or it may use any
            other value in the allowed range.  (For example, the user agent may
            use the <a>rotationAngle</a> value from the previous touch event,
            to avoid sudden changes.)
          </p>
        </dd>

        <dt>readonly attribute float force</dt>
        <dd>
          a relative value of pressure applied, in the range <code>0</code> to
          <code>1</code>, where <code>0</code> is no pressure, and
          <code>1</code> is the highest level of pressure the touch device is
          capable of sensing; <code>0</code> if no value is known.  In
          environments where <a>force</a> is known, the absolute pressure
          represented by the <a>force</a> attribute, and the sensitivity in
          levels of pressure, may vary.

          <p class="issue" id="issue-inkml">
            <strong>Issue:</strong>
            Consider aligning with other "channels" and values from
            <a href="http://www.w3.org/TR/InkML/#channelContents">Ink Markup
            Language (InkML)</a>, in addition to <a>force</a>, e.g. adding
            <a>angle</a>, <a>clientZ</a>, <a>rotation</a>, etc.
          </p>
        </dd>
      </dl>
    </section>

    <section>
      <h2><a>TouchList</a> Interface</h2>
      <p>
        This interface defines a list of individual points of contact for a
        touch event.
      </p>

      <dl title='interface TouchList' class='idl'>
        <dt>readonly attribute unsigned long length</dt>
        <dd>
          returns the number of <a>Touch</a>es in the list
        </dd>
        <dt>getter <a>Touch</a> item (in unsigned long <a>index</a>)</dt>
        <dd>
          returns the <a>Touch</a> with index <a>index</a> from the list,
          sorted in order from latest to earliest
        </dd>
        <dt><a>Touch</a> identifiedTouch (in long <a>identifier</a>)</dt>
        <dd>
          returns the first <a>Touch</a> with long <a>identifier</a> from the
          list
        </dd>
      </dl>
    </section>

    <section>
      <h2><a>TouchEvent</a> Interface</h2>
      <p>
        This interface defines the <a>touchstart</a>, <a>touchend</a>,
        <a>touchmove</a>, <a>touchenter</a>, <a>touchleave</a>, and
        <a>touchcancel</a> event types.
      </p>

      <dl title='interface TouchEvent : UIEvent' class='idl'>
        <dt>readonly attribute <a>TouchList</a> touches</dt>
        <dd>
          a list of <a>Touch</a>es for every point of contact currently
          touching the surface
        </dd>
        <dt>readonly attribute <a>TouchList</a> targetTouches</dt>
        <dd>
          a list of <a>Touch</a>es for every point of contact currently
          touching the surface, which started on the same target
        </dd>
        <dt>readonly attribute <a>TouchList</a> changedTouches</dt>
        <dd>
          a list of <a>Touch</a>es for every point of contact which contributed
          to the event
        </dd>

        <dt>readonly attribute boolean altKey</dt>
        <dd>
          <code>true</code> if the alt (Alternate) key modifier is activated;
          otherwise <code>false</code>
        </dd>
        <dt>readonly attribute boolean metaKey</dt>
        <dd>
          <code>true</code> if the meta (Meta) key modifier is activated;
          otherwise <code>false</code>.  On some platforms this attribute may
          map to a differently-named key modifier.
        </dd>
        <dt>readonly attribute boolean ctrlKey</dt>
        <dd>
          <code>true</code> if the ctrl (Control) key modifier is activated;
          otherwise <code>false</code>
        </dd>
        <dt>readonly attribute boolean shiftKey</dt>
        <dd>
          <code>true</code> if the shift (Shift) key modifier is activated;
          otherwise <code>false</code>
        </dd>
        <dt>readonly attribute EventTarget relatedTarget</dt>
        <dd>
          identifies a secondary EventTarget related to a touch event.  This
          attribute is used with the <a>touchenter</a> event to indicate the
          <a>EventTarget</a> the touch point exited, and with the
          <a>touchleave</a> event to indicate the <a>EventTarget</a> the touch
          point entered.  For other event types, this attribute must be
          <code>null</code>.
        </dd>

        <!-- Methods -->
        <dt>void initTouchEvent()</dt>
        <dd>
          initializes a TouchEvent created through the <a>DocumentEvent</a>
          interface.
          <dl class='parameters'>
            <dt>DOMString type</dt> <dd></dd>
            <dt>boolean canBubble</dt> <dd></dd>
            <dt>boolean cancelable</dt> <dd></dd>
            <dt>AbstractView view</dt> <dd></dd>
            <dt>long detail</dt> <dd></dd>
            <dt>boolean ctrlKey</dt> <dd></dd>
            <dt>boolean altKey</dt> <dd></dd>
            <dt>boolean shiftKey</dt> <dd></dd>
            <dt>boolean metaKey</dt> <dd></dd>
            <dt>TouchList touches</dt> <dd></dd>
            <dt>TouchList targetTouches</dt> <dd></dd>
            <dt>TouchList changedTouches</dt> <dd></dd>
          </dl>
        </dd>
      </dl>

      <section>
        <h3 id="event-touchstart">The <dfn class="event">touchstart</dfn>
        event</h3>
        <p>
          A user agent must dispatch this event type to indicate when the user
          places a <a>touch point</a> on the touch surface.
        </p>

        <p>
          The target of this event must be an <a>Element</a>.  If the touch
          point is within a frame, the event should be dispatched to an element
          in the <a>child browsing context</a> of that frame.
        </p>

        <p>
          If the <a>preventDefault</a> method is called on this event, it
          should prevent any default actions caused by any touch events
          associated with the same <a>active touch point</a>, including mouse
          events or scrolling.
        </p>
      </section>

      <section>
        <h3 id="event-touchend">The <dfn class="event">touchend</dfn> event</h3>
        <p>
          A user agent must dispatch this event type to indicate when the user
          removes a <a>touch point</a> from the touch surface, also including
          cases where the touch point physically leaves the touch surface, such
          as being dragged off of the screen.
        </p>

        <p>
          The <a>target</a> of this event must be the same <a>Element</a> that
          received the <a>touchstart</a> event when this <a>touch point</a> was
          placed on the surface, even if the <a>touch point</a> has since moved
          outside the interactive area of the <a>target</a> element.
        </p>

        <p>
          The <a>touch point</a> or points that were removed must be included
          in the <a>changedTouches</a> attribute of the <a>TouchEvent</a>, and
          must not be included in the <a>touches</a> and <a>targetTouches</a>
          attributes.
        </p>
      </section>

      <section>
        <h3 id="event-touchmove">The <dfn class="event">touchmove</dfn> event</h3>
        <p>
          A user agent must dispatch this event type to indicate when the user
          moves a <a>touch point</a> along the touch surface.
        </p>

        <p>
          The <a>target</a> of this event must be the same <a>Element</a> that
          received the <a>touchstart</a> event when this <a>touch point</a> was
          placed on the surface, even if the <a>touch point</a> has since moved
          outside the interactive area of the <a>target</a> element.
        </p>

        <p>
          If the values of <a>radiusX</a>, <a>radiusY</a>,
          <a>rotationAngle</a>, or <a>force</a> are known, then the user agent
          also must dispatch this event type to indicate when any of these
          attributes of a <a>touch point</a> have changed.
        </p>

        <p>
          Note that the rate at which the user agent sends <a>touchmove</a>
          events is implementation-defined, and may depend on hardware
          capabilities and other implementation details.
        </p>

        <p>
          If the <a>preventDefault</a> method is called on the <em>first</em>
          <a>touchmove</a> event of an <a>active touch point</a>, it should
          prevent any default action caused by any <a>touchmove</a> event
          associated with the same <a>active touch point</a>, such as scrolling.
        </p>
      </section>

      <section>
        <h3 id="event-touchenter">The <dfn class="event">touchenter</dfn> event</h3>
        <p>
          A user agent must dispatch this event type to indicate when a
          <a>touch point</a> moves onto the interactive area defined by a DOM
          element.  Events of this type must not bubble.
        </p>
      </section>

      <section>
        <h3 id="event-touchleave">The <dfn class="event">touchleave</dfn> event</h3>
        <p>
          A user agent must dispatch this event type to indicate when a
          <a>touch point</a> moves off the interactive area defined by a DOM
          element.  Events of this type must not bubble.
        </p>
      </section>

      <section>
        <h3 id="event-touchcancel">The <dfn class="event">touchcancel</dfn> event</h3>
        <p>
          A user agent must dispatch this event type to indicate when a touch
          point has been disrupted in an implementation-specific manner, such as
          a synchronous event or action originating from the UA canceling the
          touch, or the touch point leaving the document window into a
          non-document area which is capable of handling user interactions.
          (e.g. The UA's native user interface, plug-ins)  A user agent may
          also dispatch this event type when the user places more <a>touch
          point</a>s on the touch surface than the device or implementation is
          configured to store, in which case the earliest <a>Touch</a> object
          in the <a>TouchList</a> should be removed.
        </p>
      </section>
    </section>

    <section>
      <h2><a>DocumentTouch</a> Interface</h2>
      <p>
        The <a>DocumentTouch</a> interface provides a mechanism by which the
        user can create <a>Touch</a> and <a>TouchList</a> objects. The
        <a>DocumentTouch</a> interface must be implemented on the
        <a>Document</a> object.
      </p>

      <dl title='interface DocumentTouch' class='idl'>
        <dt>Touch createTouch()</dt>
        <dd>
          Creates a <a>Touch</a> object with the specified attributes.
          <dl class='parameters'>
            <dt>AbstractView view</dt> <dd></dd>
            <dt>EventTarget target</dt> <dd></dd>
            <dt>long identifier</dt> <dd></dd>
            <dt>long pageX</dt> <dd></dd>
            <dt>long pageY</dt> <dd></dd>
            <dt>long screenX</dt> <dd></dd>
            <dt>long screenY</dt> <dd></dd>
            <dt>optional long radiusX</dt> <dd></dd>
            <dt>optional long radiusY</dt> <dd></dd>
            <dt>optional float rotationAngle</dt> <dd></dd>
            <dt>optional float force</dt> <dd></dd>
          </dl>
        </dd>

        <dt>TouchList createTouchList()</dt>
        <dd>
          Creates a <a>TouchList</a> object containing the specified
          <a>Touch</a> objects.
          <dl class='parameters'>
            <dt>Touch[] touches</dt> <dd></dd>
          </dl>
        </dd>

        <dt>TouchList createTouchList()</dt>
        <dd>
          Creates a <a>TouchList</a> object containing a single <a>Touch</a>.
          <dl class='parameters'>
            <dt>Touch touch</dt> <dd></dd>
          </dl>
        </dd>
      </dl>
    </section>

    <section id="mouse-events">
      <h2>Interaction with Mouse Events</h2>
      <p>
        The user agent may dispatch both touch events and mouse events
        [[!DOM-LEVEL-2-EVENTS]] in response to the same user input.  If the
        user agent dispatches both touch events and mouse events in response to
        a single user action, then the <a>touchstart</a> event type must be
        dispatched before any mouse event types for that action.  If the
        <a>preventDefault</a> method of <a>touchstart</a> or <a>touchmove</a>
        is called, the user agent should not dispatch any mouse event that
        would be a consequential result of the the prevented touch event.
      </p>

      <p>
        The default actions and ordering of any further touch and mouse events
        are implementation-defined, except as specified elsewhere.
      </p>
    </section>

    <section>
      <h2>Glossary</h2>

      <dl>
        <dt><dfn>active touch point</dfn></dt>
        <dd>
          A <a>touch point</a> which is currently on the screen and is being
          tracked by the user agent.  The touch point becomes active when the
          user agent first dispatches a <a>touchstart</a> event indicating its
          appearance.  It ceases to be active after the user agent dispatches a
          <a>touchend</a> or <a>touchcancel</a> event indicating that the touch
          point is removed from the surface or no longer tracked.
        </dd>

        <dt><dfn>touch point</dfn></dt>
        <dd>
          The coordinate point at which a pointer (e.g finger or stylus)
          intersects the target surface of an interface.  This may apply to a
          finger touching a touch-screen, or an digital pen writing on a piece
          of paper.
        </dd>
      </dl>
    </section>

    <section id='issues' class='informative'>
      <h2>Issues</h2>
      <p>
        The working group maintains <a
         href='http://www.w3.org/2010/webevents/track/products/2'
        >a list of open issues in this specification</a>.  These issues may be
        addressed in future revisions of the specification.
      </p>
    </section>

    <section class='appendix informative'>
      <h2>Acknowledgements</h2>
      <p>
        Many thanks to the WebKit engineers for developing the model used as a
        basis for this spec, Neil Roberts (SitePen) for his summary of WebKit
        touch events, Peter-Paul Koch (PPK) for his write-ups and suggestions,
        Robin Berjon for developing the <a
          href="http://dev.w3.org/2009/dap/ReSpec.js/documentation.html"
        >ReSpec.js spec authoring tool</a>, and the WebEvents WG for their many
        contributions.
      </p>

      <p>
        Many others have made additional comments as the spec developed, which
        have led to steady improvements.  Among them are Matthew Schinckel,
        Andrew Grieve, and Cathy Chan. If I inadvertently omitted your name,
        please let me know.
      </p>
    </section>
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