Experimental multi-touch support for Kineticjs using Touchy

As of version 5.0.1 Kineticjs does not (yet) provide support for multi-touch events on the nodes added to the stage (it is fairly easy to add multi-touch gestures to the stage as a whole as shown in this example). This means you can not drag multiple layers/groups/shapes at the same time or react to more than one touch event at a time.

Kinetic is still under heavy development and full multi-touch support is going to be added to the core library eventually. Until then, we need a clean solution that can add multi-touch support on touch-capable devices in a simple and non-invasive way. This is what this experiment is about.

• True multi-touch (touchstart, touchmove, touchend, tap) support on any node on the stage (layer/group/shape)
• Multi-touch drag-n-drop (dragstart, dragmove, dragend) on any node
• Must behave as you would expect (e.g. dragging a shape within a draggable group should drag the group and not only the shape)
• Must honor listening : true|false directives
• Must be super-easy to use with as little user-side code as possible (ideally just an additional attribute)
• Must not patch/override anything in Kinetic's core library
• Must not break or mess up with Kinetic's single-touch event handling (incl. drag-n-drop)

At this stage file size and dependencies are not a concern (I developed this for an existing project that has loads of dependencies anyways). Lastly, overall performance should not be affected by whether multi-touch is enabled or not.

Over time I've been looking at various multi-touch libraries (there are many to choose from depending on the use case) and I've always liked the super-simple and extensible socket-like approach proposed by Touchy. Touchy's design is perfectly suited to add self-contained multi-finger handlers that we can use to add multi-touch events to Kinetic.

All we need to do is to create a kinetic Touchy plugin to do all the finger-handling for us and register the plugin on the stage container element.

• Kinetic (the best Canvas library out there :)
• Underscore (just because I am lazy and I use it everywhere)
• Touchy (kudos for making such a pretty little gem)

Additionally, if you are using Greensock's awesome GSAP tweening library (with or without the GSAP Kinetic Plugin), it will be used to handle the draw updates during dragmove (you can also specify if autoDraw should be used - see below).

You need to include Kinetic, Underscore and Touchy in your html/application. Optionally add GSAP TweenLite / TweenMax and the GSAP Kinetic Plugin. Then add Kinetic.MultiTouch.js. See example code.

Kinetic.MultiTouch adds the new namespace Kinetic.MultiTouch.

In order to make your Kinetic.Stage multi-touch aware, just inherit from Kinetic.MultiTouch.Stage instead of Kinetic.Stage:

var stage = new Kinetic.MultiTouch.Stage({
    container: 'surface-container',
    width: 400,
    height: 400
});

That's pretty much it. Kinetic.MultiTouch.Stage is basically just a stage extension that registers Touchy with the stage container element. The option object passed to the constructor is exactly the same as the one expected by Kinetic.Stage, with the following additions:

• disableSingleTouch : <boolean> (default: false): prevent Kinetic from registering its own single-touch events. This forces you to use only multitouch events only as Kinetic will not fire its own touch/mouse events any longer, but it provides better performance. In most cases this is what you want, but you can keep both if you need so.

• multitouch : <boolean> (default: false): Enable multitouch by default on the stage and its children

Unless multitouch:true is passed to the Stage constructor, by default nodes are NOT multi-touch enabled - i.e. multi-touch events are not captured and triggered. In order to make a node fire multi-touch events you need to add the multitouch property to the attributes list, for example:

var node = new Kinetic.Group({ // This can be a layer, a group, or a shape
  ...
  multitouch : true // now the node will receive/emit multi-touch events
});

Enable multi-touch drag-and-drop is equally easy:

var node = new Kinetic.Group({ // This can be a layer, a group, or a shape
  ...
  multitouch : { // now the node will receive/emit multi-touch events
    draggable : true // the node is also draggable (will move on screen and trigger drag* events)
  }

});

If you are using GSAP with the Kinetic Plugin you can pass the additional autoDraw boolean property to specify whether autoDraw should be enabled in the Kinetic Plugin (it is by default!). This is particularly useful if you have other tweens happening concurrently to your drag-and-drop that are using it. If you are not using GSAP and/or the Kinetic Plugin this option has no effect (Kinetic layer.batchDraw() is used instead).

var node = new Kinetic.Group({ // This can be a layer, a group, or a shape
  ...
  multitouch : { // now the node will receive/emit multi-touch events
    draggable : true, // the node is also draggable (will move on screen and trigger drag* events)
    autoDraw  : true // let GSAP Kinetic's plugin handle batch draws
  }

});

Multitouch directives are applied in a similar way to Kinetic's listening and draggable properties, so for example if a node is multi-touch enabled, so are its children. Kinetic default listening and draggable behaviours are preserved, so if a node is not listening to regular events it won't listen to multi-touch events either. Kinetic draggable attributes take precedence over multitouch : { draggable : true }, so if a node (or one of its ancestors) is marked as draggable, default Kinetic drag-and-drop behaviour is used instead of the multi-touch one (that is, only one node can be dragged at a time).

Touch-events are fired with a special name in order to keep them separate from regular single-touch events fired by Kinetic. They are available in the Kinetic.MultiTouch namespace as follows (the actual string names may change - this is the first thing I came out with):

Kinetic.MultiTouch.TOUCHSTART, // "touchstart:multitouch"
Kinetic.MultiTouch.TOUCHMOVE,  // "touchmove:multitouch"
Kinetic.MultiTouch.TOUCHEND,   // "touchend:multitouch"
Kinetic.MultiTouch.TAP,        // "tap:multitouch"
Kinetic.MultiTouch.DRAGSTART,  // "dragstart:multitouch"
Kinetic.MultiTouch.DRAGMOVE,   // "dragmove:multitouch"
Kinetic.MultiTouch.DRAGEND,    // "dragend:multitouch"

In order to to listen to multi-touch events you simply have to do:

node.on(Kinetic.MultiTouch.TAP, function(evt) {
  ... // evt is currently a Touchy "point", not a real TouchEvent
});

node.on(Kinetic.MultiTouch.DRAGMOVE, function(evt) {
  ... // evt is currently a Touchy "point", not a real TouchEvent
});

Kinetic 4.5.x is supported as well as Kinetic 5 up to the latest (current) version 5.0.1. The example provided uses Kinetic 5.0.1.

This is pretty much a proof of concept and it took me more time to write this README than the actual code, so things may not be 100% tested or super-smart. It should be easy enough to add this to an existing project to give it a go - and revert back if things don't work for you. Feedback is of course welcome.

This code is provided "as is" by oneoverzero GmbH.

Do whathever you want with it, have fun and be happy.