Re: Adding winding rules to Canvas

On Tue, Jan 15, 2013 at 2:59 PM, Dirk Schulze <dschulze@adobe.com> wrote:

>
> On Jan 15, 2013, at 2:53 PM, "Rik Cabanier" <cabanier@gmail.com> wrote:
>
>
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> On Tue, Jan 15, 2013 at 2:14 PM, Dirk Schulze <dschulze@adobe.com> wrote:
>
>>
>> On Jan 15, 2013, at 1:49 PM, Rik Cabanier <cabanier@gmail.com> wrote:
>>
>> > Hi Simon,
>> >
>> > I completely agree with you.
>> > As specified today, hit regions don't have support for winding. In
>> fact, it is even worse: if you have a set of drawing commands, you can't
>> get their region.
>> > The reason for this is that the path object (as currently defined)
>> simply accumulates path segments. This will wreak havoc with shapes that
>> touch or that have strokes.
>> >
>> > I have stated this a couple of times already on whatwg...
>> > What I would like to see is more like this:
>> > class PathSink implements CanvasPathMethods {
>> >   PathSink();
>> >   PathSink(DOMString); //takes SVG path syntax
>> > }
>> >
>> > class Path {
>> >   Path();
>> >   Path(PathSink, CanvasWindingRule = "nonzero");
>> >   Path(DomString text, CanvasDrawingSTyles...); // to get text outline
>> >
>> >   Path Transform(matrix Transformation);
>> >   Path Stroke(...);
>> >
>> >   Path Add(Path); // <----
>> > }
>> >
>> > The 'Add' method would not simply aggregate path segments. Instead, the
>> area of resulting path will be a union.
>> >
>> > So, for example, if you want to create a region with a stroke rectangle:
>> > var h = new PathSink();
>> > h.rect(100, 100, 200, 200);
>> > var P = new Path(h);
>> > P = P.Add(P.Stroke({'lineWidth': 10}));
>>
>> I see a problem where the concept of PathSink and Path could be confusing
>> for users. I am pretty sure that a lot of users just want to use the Path
>> object as some kind of segment container. The proposed Path object here
>> does more then these users would need and may make it more complicated. But
>> it depends on how it is specified. I could imagine how you can archive
>> both, the here mentioned PathSink would be the simple container as
>> specified in the WHAT WG spec now (maybe even less). Just a container with
>> all segments. A context would be able to take this container and fill and
>> stroke with the style applied to the the context.
>
>
> I believe that will make the Canvas API more complex.
> In addition to 'fill(optional CanvasWindingRule w = "nonzero")' and
> 'fill(Path)' we would also have to add 'fill(PathSink, optional
> CanvasWindingRule w = "nonzero")'
>
>
> Not with a currentPath attribute that takes a PathSink (alias Path)
> object. This attribute would provide a getter and setter. No other
> attribute or function would be affected.
>

Yes, that would be a way to do it.
Would the ctm by applied to the currentPath?

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> If a user was just interested in the path, they could make one at fill
> time:
>
> fill(new Path(mypathsink))
>
>
> One of the big advantage of having an atomic path is that UA's can
> optimize it in the background (ie tesselate it or resolve the winding).
>
>
>> But I would prefer naming this container Path, since it still is exactly
>> that. The object with the actually path data, with winding rules and
>> styling data could be called StyledPath. It would take a Path object,
>> represent a stroke path and a lot of other things more.
>
>
> Sure, I'm neutral on the naming convention.
>
>
>>
>
>
>> >
>> >
>> > On Tue, Jan 15, 2013 at 1:23 PM, Simon Sarris <simon.sarris@gmail.com>
>> wrote:
>> > Before we comment on your proposal I have some notes I'd like to share
>> because the current fillRule rules in the specification seem incomplete or
>> at least ill-defined.
>> >
>> > The new hit regions use a Path in the HitRegionOptions (the argument to
>> addHitRegion) in order to function, but its not clear what fill rule these
>> Path objects are using for hit-testing. Even-odd and winding fill rules
>> create different holes in a path, so it matters a good deal for hit testing.
>> >
>> > There seem to be three possibilities as implemented:
>> >       • HitRegions only ever use winding paths. This seems like a bad
>> idea.
>> >       • Whichever fillRule is defined when context.addHitRegion is
>> called determines the fillRule for that hit region's Path permanently. This
>> seems acceptable but confusing and should be clarified if it is currently
>> the case.
>> >       • The fillRule of a hit region changes dynamically as
>> context.fillRule changes. This would be a nightmare.
>> >
>> > I hope it is #2, but the specification makes no mention of this.
>> >
>> > Actually, I'd prefer that either HitRegionOptions or the Path object
>> would need to have a fillRule attribute.
>> >
>> > If the specification does adopt something similar to Cabanier's
>> suggestions then that would need to be done anyway.
>> >
>> > In short, if isPointInPath is changed to specify fillRule,
>> HitRegionOptions (the argument to addHitRegion) or the Path given in the
>> options needs to change too.
>> >
>> >
>> > Simon Sarris
>> >
>> >
>> > On Tue, Jan 15, 2013 at 3:42 PM, Rik Cabanier <cabanier@gmail.com>
>> wrote:
>> > All,
>> >
>> > there was a recent discussion on adding winding rules to canvas. As you
>> may know until now, canvas only supported even-odd winding.
>> > Maybe graphics libraries and SVG also support non-zero winding.[1][2]
>> >
>> > Mozilla exposes this currently with 'mozFillRule'. Making this part of
>> the graphics state has several drawbacks.
>> > The biggest is that fill/clip will now have to check the state every
>> time, or set/reset it. Winding is also part of path geometry.
>> >
>> > I have the following proposal:
>> > enum CanvasWindingRule { "nonzero", "evenodd" };
>> > void fill(optional CanvasWindingRule w = "nonzero");
>> > void clip(optional CanvasWindingRule w = "nonzero");
>> > boolean isPointInPath(unrestricted double x, unrestricted double y,
>> optional CanvasWindingRule w = "nonzero");
>> >
>> > proposed patches for this API can be found here:
>> > https://bugs.webkit.org/show_bug.cgi?id=105508
>> > https://bugzilla.mozilla.org/show_bug.cgi?id=827053
>> >
>> > What do people think?
>> >
>> > 1: http://www.w3.org/TR/SVG/painting.html#FillRuleProperty
>> > 2: http://en.wikipedia.org/wiki/Nonzero-rule
>> >
>> >
>>
>>
>