[whatwg] CanvasRenderingContext2D with addPath, currentPath

[Rik Cabanier]

On Mon, Nov 4, 2013 at 11:25 AM, Rik Cabanier <cabanier at gmail.com> wrote:

>
>
>
> On Mon, Nov 4, 2013 at 1:49 AM, Jürg Lehni <lists at scratchdisk.com> wrote:
>
>> > What's the use case?
>> >
>> > I intentionally didn't add this to the spec when I was adding the last
>> set
>> > of path-related features, because it seems entirely redundant with Path
>> > objects. I thought we'd want people to move away from using the implicit
>> > path, rather than making it more powerful.
>>
>> I like this feature a lot. One advantage to not underestimate is the
>> amount of effort it takes to change existing code to make use off the new
>> Path feature, while staying backward compatible with older browsers that
>> don't implement this spec. For example, in Paper.js it took only three
>> added lines of code to use cached paths if they exist rather than redrawing
>> them each time
>>
>
> Do you think getCurrentPath should return a path in user space or in the
> current transformation matrix?
>

Answering my own question, when reading the canvas spec [1], it should be
in user space:

When the intended path is a
Path<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#path>
object,
the coordinates and lines of its subpaths must be transformed according to
the CanvasRenderingContext2D<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#canvasrenderingcontext2d>
 object's current transformation
matrix<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#transformations>
when
used by these methods (without affecting the
Path<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#path>
object
itself). When the intended path is the current default
path<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#current-default-path>,
it is not affected by the transform. (*This is because transformations
already affect the **current default
path*<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#current-default-path>*
when
it is constructed, so applying it when it is painted as well would result
in a double transformation*.)


In light of this, does anyone have objections to these 2 new methods:

Path getCurrentPath();

void setCurrentPath(Path);


With the path in user space (so it is not affected by the CTM).

1:
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#drawing-paths-to-the-canvas