[ttml2] Upright orientation involves more than just glyph orientation

r12a has just created a new issue for https://github.com/w3c/ttml2:

== Upright orientation involves more than just glyph orientation  ==
10.2.46 tts:textOrientation
http://w3c.github.io/ttml2/spec/ttml2.html#style-attribute-textOrientation

> If the value of this attribute is upright, then, in vertical writing modes, glyphs from horizontal scripts are set upright, i.e., using their nominal orientation in horizontal text, while glyphs from vertical scripts are not affected. In addition, for purposes of bidirectional processing, this value causes all affected characters to be treated as strong left-to-right, i.e., to be treated as if a tts:direction of ltr and tts:unicodeOverride of override were applied.

There are additional things to bear in mind here. The treatment as strong left-to-right will put arabic script characters in the correct visual order down the vertical line, but it should also be said that the characters should use the isolated form.  Furthermore, the rotations should be applied to groups of glyphs that constitute a grapheme cluster, so that for example indic syllables remain together. (Although some consonant clusters are not fully encompassed by grapheme clusters even, in scripts like devanagari.)

I think there's some wording to this effect in the CSS spec that you could look at.

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/281 using your GitHub account

Received on Monday, 13 March 2017 20:05:13 UTC