Re: [css-writing-modes-3] central baseline of text with 'text-orientation: upright'

Le 2014-09-02 03:46, Koji Ishii a écrit :
> 2014-08-29 22:47 GMT-04:00 G=E9rard Talbot <www-style@gtalbot.org>:
>> If this is the case, then a central baseline can be determined for =
> text with
>> 'text-orientation' set to 'upright' but is this feature (characters =
> designed
>> to have a square character frame) also the case for other vertical =
> scripts?
> 
> 
> I=92m not sure if I understand your question,

Hello,


My original question was:

How can there be a central baseline for text with 'text-orientation' set 
to 'upright'?

Figure 11 in
http://www.w3.org/TR/css-writing-modes-3/#intro-baselines
is

http://www.w3.org/TR/css-writing-modes-3/script-preferred-baselines.gif

and we do not see any central baseline for text when 'text-orientation' 
is set to 'upright' .

Figures 11 and 12 in
http://www.w3.org/TR/css-writing-modes-3/#intro-baselines
only show various baselines when 'text-orientation' is set to 
'sideways-left' or 'text-orientation' is set to 'sideways-right' or with 
'writing-mode' set to 'horizontal-tb'. But not when 'text-orientation' 
is set to 'upright'.

There is no vertical displayed line that goes through glyphs shown in 
sections 4.1 and 4.2 when 'text-orientation' is set to 'upright'. And 
glyphs themselves are not using the same width: eg. an "i" (lowercase i) 
is not as wide as a "W" (uppercase w). See quick ascii example that 
follows.


> sorry if the following are =
> all my misunderstandings, but I guess understanding the vertical 
> metrics =
> in OpenType might help you.
> 
> OpenType defines vmtx/VORG to define vertical baseline for glyphs; to 
> be =
> more accurate, vertical origins and advances.

VertOriginY seems (I am really not sure of this) to be the vertical 
offset of the em box; I do not know what vertical advance could be.

> I can=92t find good =
> pictures that explains this table, p. 23 of this PPT[1] may help. In 
> the =
> picture, the blue small circle indicates the vertical origins.

The small blue square seems to be the horizontal center of the glyph 
character square. The 663 and 880 values in the example (for "g" glyph) 
of p. 23 of
http://blogs.adobe.com/CCJKType/files/2012/06/afdko-mhattori-20120625.pdf
seem to indicate the vertical offset or a vertical position of such 
glyph.

"
通常は全角ローマン体の縦書きの位置補正に
使われる
かな縦書きプロポーショナルを実現するため
には
"
is translated as
"
To position correction of vertical writing em roman usually
Will be used
In order to realize the vertical writing Kana Proportional
To the
"

So, those are offsets to find the respective baselines (alphabetic and 
central).

But my question remains:

Assume that the following inline text has 'text-orientation' set to 
'upright':

  K
  i
  W
  i

and assume that characters do not have the same character width. Now, 
where would the central baseline be drawn?

... unless each and all glyphs must use the same character width and 
that the central baseline traverse the horizontal center of each glyph, 
there is a problem here.

Gérard

> As in the =
> picture, upright Latin glyphs are expected to have their vertical =
> origins at the center of top edges.
> 
> So all normal CSS baseline rules apply assuming:
> a. Baselines are drawn vertically
> b. The vertical origins of glyphs are placed to the baseline according 
> =
> to the normal CSS rules
> 
> Does this help your understanding?
> 
> Note that in the real world, not all fonts have these tables, but UA is 
> =
> expected to synthesize when not available.
> 
> [1] =
> http://blogs.adobe.com/CCJKType/files/2012/06/afdko-mhattori-20120625.pdf
> 
> /koji

Received on Wednesday, 3 September 2014 18:58:36 UTC