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 Post subject: Property Values for the East Asian Orientation Property
PostPosted: Mon Jan 02, 2012 3:17 pm 
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Joined: Wed Dec 07, 2011 3:01 am
Posts: 71
Property Values for the East Asian Orientation Property needs to be a little more clarified. I was reviewing UTR#50 with JLREQ authors and several Japanese people here in Japan, but nobody understands differences very well (including myself), and many understand differently from others. With such situation, it is not easy to review; when we find issues, oftentimes people concludes to different value although they're saying the same thing.

Also, one concern I have for T is that it doesn't indicate orientation at all. Since one of the goal of this property is to define orientation so that application can use fallback-level rendering using fonts without vertical flow support, we should define them clearly.

My proposal is as follows:

U: is upright, but fonts are allowed to have different glyphs from their horizontal glyphs, primarily for design purposes.
T: is upright, but fonts are required to have different glyphs from their horizontal glyphs if they support vertical flow.
S: is sideways, and applications may assume glyphs do not change.
SB: is sideways, but fonts are allowed to have different glyphs from their horizontal glyphs.
ST: is sideways, but fonts are required to have different glyphs.

I guess it's not too far from the current definitions. Points of this proposal are:
1. T is split to upright and sideways, so that applications know the orientations.
2. Split glyph differences by design and typographic requirements. Some people wants to classify some code points to T because some fonts want to have different design in vertical flow. We should distinguish such cases from where glyph position or shape needs to be changed for typographic requirements.

This definition allows applications to safely ignore vertical alternate information for S, and also since it clarifies orientations, it allows fallback rendering of T for fonts that do not support vertical flow nicely.


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 Post subject: Re: Property Values for the East Asian Orientation Property
PostPosted: Fri Jan 06, 2012 5:44 pm 
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Joined: Fri Dec 04, 2009 9:25 pm
Posts: 76
Quote:
one concern I have for T is that it doesn't indicate orientation at all


Correct, because it cannot.

Think of it this way: the published code charts show representative glyphs for text that is displayed horizontally. To get the representative glyphs for vertical texts:
- if EAO is U, use the same representative glyph as in the (horizontal) code chart
- if EAO is S or SB, rotate the representative glyph of the (horizontal) code chart 90 degree clockwise
- if EAO is T, get the representative glyph from section 5.4, table 3, column V.

That's all EAO is about. As usual, representative glyphs are just that, representative. There is nothing that prevent a from having different ink for horizontal and vertical texts.

IMO, TR50 is not the place to regulate the interaction between layout engines and fonts, that belongs to things like the OpenType, AAT and Graphite specifications (in particular things like "applications may assume glyphs do not change" are not appropriate).


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 Post subject: Re: Property Values for the East Asian Orientation Property
PostPosted: Sat Jan 07, 2012 4:42 am 
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Joined: Wed Dec 07, 2011 3:01 am
Posts: 71
Thank you for the comment.
emuller wrote:
- if EAO is U, use the same representative glyph as in the (horizontal) code chart

When you say "use the same representative glyph as in the (horizontal) code chart" for U, does it allow slight design changes by horizontal/vertical, or does it force to use exactly the same glyph? Does it allow font designers to put different start/end brush shapes for vertical?
If you want to prohibit such design changes for U (I believe you were thinking so before if I didn't misunderstand,) I'd like to ask several code points to classify to T.
emuller wrote:
- if EAO is S or SB, rotate the representative glyph of the (horizontal) code chart 90 degree clockwise

From the description, S and SB are the exactly the same. What exactly the differences between the two are?
While reviewing S and SB, it's hard to say which value is correct without clear definitions. You know, there are code points that are hard to say "if it's a bracket" or not. Can you please consider clarifying more on these definitions?
emuller wrote:
Quote:
one concern I have for T is that it doesn't indicate orientation at all

Correct, because it cannot.

- if EAO is T, get the representative glyph from section 5.4, table 3, column V.

For instance, U+301C or U+30FC in Table 3 are sideways + glyph change, while U+3041 or U+3300 are upright + glyph change. I would like to distinguish them, as it would help application layers to render better results without good supports in fonts.


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 Post subject: Re: Property Values for the East Asian Orientation Property
PostPosted: Sat Jan 07, 2012 7:02 am 
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Joined: Wed Dec 07, 2011 3:01 am
Posts: 71
emuller wrote:
IMO, TR50 is not the place to regulate the interaction between layout engines and fonts, that belongs to things like the OpenType, AAT and Graphite specifications (in particular things like "applications may assume glyphs do not change" are not appropriate).

Follow up on this part; I agree with you on this.

However, the TR50 should define what the exact meaning of each value, and and how one value differs from another, and that's what I'm asking here.

My wording may not be good, I admit that, but whether vertical glyphs can or should not differ from its horizontal counterpart is also part of TR50 I believe. How to implement it is not.


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