[whatwg] new constructor method for Path2D

[Rik Cabanier]

On Thu, Mar 6, 2014 at 2:28 AM, Dirk Schulze <dschulze at adobe.com> wrote:

>
> On Mar 5, 2014, at 11:54 PM, Rik Cabanier <cabanier at gmail.com> wrote:
>
> > On Wed, Mar 5, 2014 at 2:43 PM, Ian Hickson <ian at hixie.ch> wrote:
> >
> >> On Wed, 5 Mar 2014, Jeff Muizelaar wrote:
> >>> On Mar 5, 2014, at 5:34 PM, Ian Hickson <ian at hixie.ch> wrote:
> >>>> On Wed, 5 Mar 2014, Rik Cabanier wrote:
> >>>>>
> >>>>> To work around this, we could add a couple of constructor methods to
> >>>>> the 2D context:
> >>>>>
> >>>>> Path2D createPath();
> >>>>>
> >>>>> Creates a new empty Path object [...]
> >>>>
> >>>> This used to be how many Web APIs worked, but over the years we've
> >>>> received enormous volumes of feedback to the effect that
> >>>> constructor-based APIs are way better than factory-based APIs. Is
> >>>> there no way we could at least have all the canvases within a Document
> >>>> in Firefox use the same backend? It would be really unfortunate to
> >>>> have to use factories here to get around an implementation detail in
> >>>> one browser.
> >>>
> >>> The choice of backend depends on the size of the canvas. So it wouldn't
> >>> be easy to have all canvases within a document use the same backend.
> >>
> >> Ah, ok.
> >>
> >> This makes a factory method somewhat less useful, because what if the
> >> canvas changes size later? Do all the paths have to be "re-bound"?
> >
> >
> > for optimal performance, yes.
> > Rescaling a canvas is not that common of a scenario though.
>
> To switch the context of a created Path2d, you still need an abstraction
> of the path, don't you? Some platforms are not able to return the created
> path. Many more are not able to return an unflattened path (which might not
> be an issue). So if you might need an abstraction anyway, is the
> performance problem that you need to do it on each drawing operation? There
> are clearly ways to work around such an issue.


At least for the Firefox backends (Cairo, Skia, D2D and Core Graphics) this
is not a problem. Paths are just groups of line segments so it should be
trivial to walk them


> >
> > Maybe this hint would be useful for Chrome since they switch to software
> > under certain circumstances too
>
> I am unsure if it would. It is the same graphic library that manages the
> path object. Even if uses a different backend.
>

It seems like it could help but the Chrome people would know best.