[whatwg] Canvas "coordinate space units"

David Flanagan david at davidflanagan.com
Thu Jul 15 11:25:09 PDT 2010

Philip Taylor wrote:
> On Wed, Jul 14, 2010 at 10:33 PM, Aryeh Gregor <Simetrical+w3c at gmail.com> wrote:
>> On Wed, Jul 14, 2010 at 3:03 PM, David Flanagan <david at davidflanagan.com> wrote:
>> [...]
>>> It is used in the definition of the lineWidth attribute as well. Chrome,
>>> Firefox and Opera all scaled lineWidth and Phillip Taylor's test suite
>>> expects this behavior as well.
>> I can't find where it says lineWidth should be scaled . . .
> In "Drawing model": "For shapes, the current fill, stroke, and line
> styles must be honored, and the stroke must itself also be subjected
> to the current transformation matrix". Also it says "(Transformations
> affect the path when the path is created, not when it is painted,
> though the stroke style is still affected by the transformation during
> painting.)". So I think it's clear enough that the width of the stroke
> will be scaled by the CTM.

Thanks for pointing these sections out, Phillip.  I was looking for a 
statement specific to transformations of the lineWidth and missed these 
more general statements about stroke style.  Still, they make things a 
lot clearer.


> (I don't think it's clear exactly *how* the stroke will be scaled, or
> rotated or translated or skewed etc - I'd like it more if everything
> was specified in precise geometric algorithms, rather than fluffy
> prose, but it seems like implementations interoperate anyway and test
> cases can tell when they get it wrong so there's probably not much
> practical benefit in rewriting everything much more precisely.)

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