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westures

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Westures is a robust multitouch gesture engine for JavaScript. Each gesture is capable of working seamlessly as touch points are added and removed, with no limit on the number of touch points, and with each touch point contributing to the gesture.

Visit this page for an example of the system in action: Westures Example.

The library achieves its goals without using any dependencies except for its own core, yet maintains usability across the main modern browsers. Transpilation may be necessary for this last point to be achieved, as the library is written using many of the newer features of the JavaScript language. A transpiled bundle is provided, but the browser target list is arbitrary and likely includes some bloat. In most cases you will be better off performing bundling, transpilation, and minification yourself.

This module includes westures-core as well as a base set of gestures.

Westures is a fork of ZingTouch.

Quick Example

// Import the module.
const wes = require('westures');

// Declare a region. The default is the window object, but other elements like
// the document body work too.
const region = new wes.Region();

// Combine an element and a handler into a Gesture.
const pan = new wes.Pan(document.querySelector('#pannable'), (data) => {
  console.log(data.translation.x, data.translation.y);
})

// And add the gesture to the region.
region.addGesture(pan)

Table of Contents

Overview

There are nine gestures defined in this module:

Name # of Inputs Emit Phase Recognized Input Behaviour
Pan 1+ Move Sliding around the screen
Pinch 2+ Move Moving together or apart
Press 1+ Move Held down without moving
Pull 1+ Move Moving away from or toward a fixed point
Rotate 2+ Move Rotating around each other
Swipe 1+ End Moving quickly then released
Swivel 1+ Move Rotating around a fixed pivot point
Tap 1+ End Quickly pressing and releasing
Track 1+ All Track locations of all active pointers

See the documentation for more information about each gesture.

Note that all x,y positions are obtained from the corresponding clientX and clientY properties of the input event.

Basic Usage

Importing the module

const wes = require('westures');

Declaring a Region

First, decide what region should listen for events. This could be the interactable element itself, or a larger region (possibly containing many interactable elements). Behaviour may differ slightly based on the approach you take, as a Region will perform locking operations on its interactable elements and their bound gestures so as to limit interference between elements during gestures, and no such locking occurs between Regions.

If you have lots of interactable elements on your page, you may find it convenient to use smaller elements as regions. Test it out in case, and see what works better for you.

By default, the window object is used.

const region = new wes.Region();

Instantiating a Gesture

When you instantiate a gesture, you need to provide a handler as well as an Element. The gesture will only be recognized when the first pointer to interact with the region was inside the given Element. Therefore unless you want to try something fancy the gesture element should probably be contained inside the region element. It could even be the region element.

Now for an example. Suppose you have a div (id 'pannable', although this is irrelevant from Westures' perspective) within which you want to detect a Pan gesture. First we need to find the element.

const pannable = document.querySelector('#pannable');

And we also need a handler. This function will be called whenever a gesture hook returns non-null data. For Pan, this is just the move phase, but the handler doesn't need to know that. The data returned by the hook will be available inside the handler.

function panLogger(data) {
  console.log(data.translation.x, data.translation.y);
}

Now we're ready to combine the element and its handler into a gesture.

pan = new wes.Pan(pannable, panLogger);

We're not quite done though, as none of this will actually work until you add the gesture to the region.

Adding a Gesture to a Region

Simple:

region.addGesture(pan);

Now the panLogger function will be called whenever a pan gesture is detected on the #pannable element inside the region.

Implementing Custom Gestures

The technique used by Westures (originally conceived for ZingTouch) is to filter all user inputs through four key lifecycle phases: start, move, end, and cancel. Gestures are defined by how they respond to these phases. To respond to the phases, a gesture extends the Gesture class provided by this module and overrides the method (a.k.a. "hook") corresponding to the name of the phase.

The hook, when called, will receive the current State object of the region. To maintain responsiveness, the functionality within a hook should be short and as efficient as possible.

For example, a simple way to implement a Tap gesture would be as follows:

const { Gesture } = require('westures');

const TIMEOUT = 100;

class Tap extends Gesture {
  constructor() {
    super('tap');
    this.startTime = null;
  }

  start(state) {
    this.startTime = Date.now();
  }

  end(state) {
    if (Date.now() - this.startTime <= TIMEOUT) {
        return state.getInputsInPhase('end')[0].current.point;
    }
    return null;
  }
}

There are problems with this example, and it should probably not be used as an actual Tap gesture, it is merely to illustrate the basic idea.

The default hooks for all Gestures simply return null. Data will only be forwarded to bound handlers when a non-null value is returned by a hook. Returned values should be packed inside an object. For example, instead of just return 42;, a custom hook should do return { value: 42 };

If your Gesture subclass needs to track any kind of complex state, remember that it may be necessary to reset the state in the cancel phase.

For information about what data is accessible via the State object, see the full documentation here. Note that his documentation was generated with jsdoc.

Data Passed to Handlers

As you can see from above, it is the gesture which decides when data gets passed to handlers, and for the most part what that data will be. Note though that a few properties will get added to the outgoing data object before the handler is called. Those properties are:

Name Type Value
centroid Point2D The centroid of the input points.
event Event The input event which caused the gesture to be recognized
phase String 'start', 'move', 'end', or 'cancel'
type String The name of the gesture as specified by its designer.
target Element The Element that is associated with the recognized gesture.

If data properties returned by a hook have a name collision with one of these properties, the value from the hook gets precedent and the default is overwritten.

Changes

See the changelog for the most recent updates.

Nomenclature and Origins

In my last year of univerisity, I was working on an API for building multi-device interfaces called "WAMS" (Workspaces Across Multiple Surfaces), which included the goal of supporting multi-device gestures.

After an extensive search I found that none of the available multitouch libraries for JavaScript provided the fidelity I needed, and concluded that I would need to write my own, or at least fork an existing one. ZingTouch proved to the be the most approachable, so I decided it would make a good starting point.

The name "westures" is a mash-up of "WAMS" and "gestures".

Issues

If you find any issues, please let me know!

Links

westures

westures-core


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