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Re: [css-shapes] Purpose of fill-rule not specified

From: Alan Stearns <stearns@adobe.com>
Date: Fri, 24 Jul 2015 20:48:26 +0000
To: Tom Potts <karaken12@gmail.com>, CSS WG <www-style@w3.org>
Message-ID: <1B43EA17-8A53-4D7A-88ED-D35393B3C3A4@adobe.com>
On 7/23/15, 11:54 AM, "Tom Potts" <karaken12@gmail.com> wrote:

>
>
>On 23 July 2015 at 16:38, Alan Stearns <stearns@adobe.com> wrote:
>>
>> On 7/23/15, 8:17 AM, "Tom Potts" <karaken12@gmail.com> wrote:
>>
>> >Okay, that makes sense, although I think you need a note to be clear 
>>that
>> >the shape used in shape-outside is calculated as if nonzero was 
>>specified,
>> > otherwise it starts to look inconsistent when you consider the effect 
>>of
>> >infinitely thin spurs. (See this demo
>> ><http://codepen.io/karaken12/pen/bdmbwg?editors=110> to
>> > see what I mean.)
>>
>> I agree the inconsistency is weird. We should probably have the same
>> behavior for both cases, and I don’t have a strong preference for either
>> behavior. Do you have an argument for one over the other?
>
>I don't have a strong preference either, as long as the expected 
>behaviour is clear. My (mild) preference is for the fill-rule setting to 
>be respected, because in future levels a central void might be useful 
>(I'm thinking about the examples in
> earlier versions of the spec with text flowing "through" a float) and if 
>that ever happens we'd either need to change the spec at that point, or 
>admit inconsistent behaviour. I think the current behaviour in Chrome 
>with spurs (ignored for basically everything)
> fits well with that.
> 
>>
>> >
>> >Was there any particular reason for choosing this behaviour, by the 
>>way?
>> >As I mentioned, it wasn't what I expected on reading the spec, but I
>> >can't find any discussion as to why it works this way.
>>
>> I don’t see where this ever came up on the list, so it’s likely my fault
>> for not forwarding on some implementation discussion.
>
>It'd be interesting to know why, if there's a quick answer, but I don't 
>think the details matter too much. If it's an implementation detail 
>that's fine, but if there's a good reason to prefer one or the other it'd 
>be good to have that reason recorded
> somewhere.

OK, I searched through my email archive and found that I was entirely 
incorrect. Float wrapping *should* respect fill-rule as you expected. I 
had internalized a temporary implementation limitation. The Chrome and 
WebKit behavior for your case 3 should be considered a bug.

This came up when we separated out our shape-inside experiments from the 
shape-outside implementation. This allowed us to use a much simpler 
algorithm, but it had a drawback of breaking support for fill-rule (which 
up to that point had been working correctly). Hans Muller blogged about 
this 16 months ago (see the “Degenerate Polygons” section):

http://hansmuller-webkit.blogspot.com/2014/03/a-simpler-algorithm-for-css-s

hapes.html

I didn’t mention this on www-style at the time because I considered it a 
temporary regression. And then I forgot about it. I’ll add an example to 
the spec that shows what should happen. Then we’ll see whether 
implementations will match that expectation.

Thanks,

Alan
Received on Friday, 24 July 2015 20:48:57 UTC

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