Re: [ft-devel] [Patch] CJK autofit/autohint blue zones

[Just Fill Bugs]

On 04/20/2011 02:16 PM, address@hidden wrote:
> Q1) The vertical bluezones are essential?
> 
> In vertical CJK typography, there would be the requirement
> to align long center stems (of the glyphs like "十", "土",
> "王"), to pretend the centerlines of the glyphs are aligned.
> However, I'm questionable if there is a requirement to align
> non-center stems to be aligned. Maybe the alignment of the
> vertical stems of the radical-"enclosure" glyphs (like "回",
> "囚", "困") or radical-"gate" glyphs (like "門", "開", "閉" )
> may improve the quality. But I'm questionable if there is
> the requirement to align the left vertical stems of radical
> "mound" glyphs (like "阿", "防", "阻"), or radical "mouse"
> glyphs (like "叫", "叩", "叱").
> 
> Maybe my impression about vertical bluezone is based on the
> typography in Japanese market, so, I don't think this is
> generic. Please let me know if there is such requirement in
> Chinese or Korean typography.

There is require to align side of glyph in vertical writing in Chinese.

For the vertical blue zone. Partly because I kinda misunderstood the
icfb tag describe by Adobe at

http://partners.adobe.com/public/developer/opentype/index_tag4.html#ideoembox

I guess it mostly talking about horizontal alignment using icfb, while I
mistook it's also
 used for vertical layout.

Another reason I consider to add vertical blue zone is that I don't know
how vertical layout looks like at small size on screen. Without blue
zone, the width of glyphs will vary quite frequently at small points. I
don't know how our eyes tolerant to that.

Just better safe than sorry. Of course it can always be removed now and
add back by request.

> 
> Q2) What kind of glyphs are good to calculate the fill bluezone?
> 
> It seems that the characters to calculate the top-fill bluezone
> is collected from the characters which have some peak/apex in
> upper boundary but have no horizontal strokes. Is it possible to
> reduce the testing characters by using the characters with the
> the radicals with peak, like, "京" (radical lid), "令" (radical
> man), "安" (radical roof), "床" (radical dotted-cliff), "草"
> (radical grass)?
> In my personal opinion, using "dot beyond horizontal stroke" is
> good benchmark to reserve the room of the dot in low resolution.
> 

Top fill really just verticle stems and dot like strokes which are more
extruded than horizontal stems.

I agree. For complex enough character, dot like strokes are more
representative.

> 
> However, some strokes have inconstant line width issues;
> the top horizontal stroke of "面" is typical example.
> "看" in IPA Gothic shows similar issue.

Maybe this can be alleviated by take into account the accumulated small
'drift' of alignment of previous stems as aflatin2.c did.

And turn on grey scale rendering should help too.

> 
> I think your patch is very good but the list of testing
> characters requires more discussion. So I will try to add
> new API for the client to modify the list.
> 

Thanks for your work!