Canvas Wrapper with getTransform()

The Canvas spec does not include a getTransform() method, so after performing rotation/scale/translation operations there is no way to work out where you really are.

So, I have created a wrapper class, which sits over the top of Canvas, and should behave exactly the same, except you now have a getTransform() method which returns a matrix such that the following doesn't do anything:

var m = ctx.getTransform();
ctx.setTransform( m[0][0], m[0][1], m[1][0], m[1][1], m[2][0], m[2][1] );

To use, add the following line:

<script type="text/javascript" src="canvas_wrapper.js"></script>

then wrap your canvas object in a CanvasWrapper, ie:

ctx = new CanvasWrapper(document.getElementById("canvas").getContext("2d"));

It works by duplicating Canvas' matrix operations, and mimicking the Canvas interface. An annoyance is that Canvas has public fields, instead of accessor methods, so I can't tell when it has been changed and have to update the canvas state before any drawing call.

Update 10/2/2013: Thanks to Heikki Pora for a patch adding some missing features.

Update 19/5/2015: The HTML Spec now includes context.currentTransform but it doesn't work for me in Firefox or Chromium, ctx.mozCurrentTransform does work in Firefox.