Re: [css-writing-modes] Propose to weaken upright rendering of horizontal-only scripts

On 28/4/15 19:02, Koji Ishii wrote:
> I’d like to propose to weaken spec words when rendering
> horizontal-only scripts in upright.
>
> One in text-orientation: upright, the proposed change is from:
 >   characters from horizontal-only scripts are rendered upright
> to:
>   characters from horizontal-only scripts should be rendered upright

I don't think this should be weakened to a "should", as this would allow 
an implementation to ignore the 'upright' value and render Latin (etc) 
characters as if it were 'mixed' or 'sideways-right'. We shouldn't leave 
room for that to be claimed as a conforming implementation of 
text-orientation:upright.

>
> Then in the definition of “upright characters”[2], from:
 >   characters from horizontal cursive scripts (such as Arabic) are
 >   shaped in their isolated forms when typeset upright
 > to:
 >   characters from horizontal cursive scripts (such as Arabic) should
 >   be shaped in their isolated forms when typeset upright
 > or we could be more descriptive how we’d like to weaken.

Again, I'd prefer not to weaken in this way; I think it's clear that
cursive horizontal scripts, when typeset in vertical upright mode,
should use isolated forms rather than their normal (horizontal) cursive 
joining. (Firefox Nightly currently gets this wrong, but should be fixed 
very shortly.)

What's less clear, IMO, is how to handle the complex Indic scripts where 
reordering and clustering behavior is involved.

>
> The motivation is that I know little about if every single
> horizontal-only script can really render upright with this
> definition. I know there are people who knows it better than me, but
> a discussion of Jonathan and Behdad[3] indicated me that there are
> more we need to study, and I’m afraid to define it normatively with
> our current knowledge.

I agree there are gaps in our knowledge of how best to render some 
scripts in this mode, but rather than weakening the current spec text, 
which I think is OK as far as it goes, perhaps we should just have a 
note that the behavior of complex scripts such as Indic and SE Asian in 
vertical upright is not clearly defined yet.

JK

>
> Further more, tests discovered that all browsers are not able to
> render some each own set of horizontal-only characters in upright.
> Fixing all of such issues would require broad knowledge of scripts in
> the world, which would require quite a work, and I think it is far
> beyond the basic vertical flow that better to defer.
>
> Thoughts?
>
> [1] http://dev.w3.org/csswg/css-writing-modes-3/#valdef-text-orientation-upright
>[2] http://dev.w3.org/csswg/css-writing-modes-3/#typeset-upright
> [3] http://lists.freedesktop.org/archives/harfbuzz/2015-April/004819.html
>
>  /koji
>
>
>

Received on Wednesday, 29 April 2015 08:40:35 UTC