[whatwg] Proposal: change 2D canvas currentTransform to getter method

Rik Cabanier cabanier at gmail.com
Thu Mar 20 11:11:10 PDT 2014

On Thu, Mar 20, 2014 at 10:52 AM, Justin Novosad <junov at google.com> wrote:

> Hello all,
> The recently added currentTransform attribute on CanvasRenderingContext2D
> gives shared access to the rendering context's transform. By "shared", I
> mean:
> a) this code modifies the CTM:
> var matrix = context.currentTransform;
> matrix.a = 2;
> b) In this code, the second line modifies matrix:
> var matrix = context.currentTransform;
> context.scale(2, 2);
> This behavior is probably not what most developers would expect.
> I would like to propose changing this to a getter method instead.  We
> already have a setter method (setTransform).
> In another thread entitled "Canvas Path.addPath SVGMatrix not optimal",
> Dirk Schulze proposed using the name getCTM, which would be consistent with
> the SVGLocatable interface, where getCTM returns an SVGMatrix. On the other
> hand, we could call it getTransform to be consistent with the existing
> setTransform on CRC2D. Opinions?

getCTM is nice and short and matches SVG. getCurrentTransform is more clear
so I'm fine with either one.

Since setTransform takes 6 arguments, it would be a bit strange that
getTransform would return an SVGMatrix.

> Perhaps we should also have an overload of
> setTransform (or setCTM) that would take an SVGMatrix

yes, it would be nice to have a transform/setTransform with that signature

> First of all, have any browsers shipped currentTransform yet?


> Thoughts?
>     -Justin Novosad

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