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    Pointer.js

    Pointer.js consolidates pointer-like input models across browsers and devices.
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    Important note (August 7, 2013)

    This project is deprecated.

    For your future pointer event needs, please use this PointerEvents polyfill, part of the Polymer Project.

    An early pointer events polyfill

    For background and motivation, see this blog post: http://smus.com/mouse-touch-pointer/.

    Implementation

    This is a library that enables MSPointer*-style pointer events in all browsers.

    Pointer events

    The whole point of pointer.js is to use pointer events instead of mouse and touch*. You can do this by subscribing to these events in the same way as you would regular events:

    var el = document.querySelector(mySelector);
    el.addEventListener('pointerdown', function(e) {
      // ...
    });
    

    Approach: override addEventListener to intercept pointer* events. (Theoretical alternative: have an explicit el.emitPointers call.)

    As soon as you start listening for pointer* events, both mouse and touch events are hijacked, and do not fire.

    The event payload for a pointer event includes the following important features:

    • {String} pointerType - the kind of pointer it is (touch, mouse, pen)
    • {Object} originalEvent - the original event payload from the underlying event.
    • {Function} getPointerList() - gets the list of active pointers (ie mouse pressed, fingers on the screen).

    The bottom line is that you code your input to a single spec: pointer events from pointer.js. The library abstracts all of the input differences for you under the consolidated model.

    Pointer API

    Events: pointerdown, pointermove, pointerup

    Event payload class: originalEvent, pointerType, getPointerList()

    Pointer class: clientX, clientY, screenX, screenY, pageX, pageY, tiltX, tiltY, pressure, hwTimestamp, pointerType, identifier

    Gesture events

    Now that we have a solid touch/mouse/stylus abstraction, we can build higher level gestures on top. Some interesting events to support are tap, double tap, longpress, swipe, pinch-zoom, and rotate.

    Gesture API

    Emit new gesture* events. For example, gesturedoubletap, gesturelongpress, gesturescale, etc. This is incompatible with Safari's gesturestart events, but in the future can also be consolidated under one umbrella.

    This is done with the same addEventListener hack as is used for pointer events. Each of these gesture* events has a recognizer associated with it. If, for example, gesturescale is specified, the pointer-event-based recognizer gets pulled into the event loop.

    Each gesture has a custom event associated with it. This function takes an HTMLElement as its only argument. The following gestures are supported:

    gesture           gesture event
    ===================================
    Double Tap        gesturedoubletap
    Long Press        gesturelongpress
    Scale             gesturescale
    

    This is a nice place to contribute if you're so inclined. Gesture recognizers can easily be plugged into this architecture. They are completely standalone and can be registered easily. For an example, take a look at the doubletap handler.

    The scale gesture implements a pinch-zoom and provides the scaling factor as part of the event payload through evt.scale.

    Demos

    Open questions

    • Will the way addEventListener is overridden cause problems in the future?

    • Is the overhead of firing a custom event vs. calling a function too high? See this test on jsperf.com

    • Does the gesture approach make sense on iOS, which provides built-in gesture support? How to consolidate?

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