- From: ChangSeok Oh via GitHub <sysbot+gh@w3.org>
- Date: Fri, 05 May 2023 21:11:51 +0000
- To: public-css-archive@w3.org
> So the fallback used is the "average" _vertical_ advance, which in turn is based on the font's ascent + descent, as there's no vertical-mode equivalent to the OS/2 table's `xAvgCharWidth` field. Thanks for the explanation. If I understand correctly, the advance height differs slightly from the height (i.e., the sum of ascent and descent). The advance height indicates the next vertical pen position after a glyph so that it can include some marginal space as well as ascent and descent [1]. So, strictly speaking, the aveCharWidth can also cause a difference from what the spec states. `using the *advance* height of “水”`. Or else, is what the spec really wants to say `using the height of “水”`, not the advance height? [1] https://freetype.org/freetype2/docs/glyphs/glyphs-3.html > I think this is better than falling back to ic-width because of the possibility of significantly non-square fonts. I know most common fonts will have square or near-square glyphs for 水 and other ideographs, but in a highly-stylised (e.g. condensed or expanded) font this might not be true. So Gecko's implementation is instead based on the assumption that in vertical mode, all characters will simply get the same fixed advance (height) if specific vertical metrics are not present. O.K. If we keep ic-height, the spec at least needs to be updated, clarifying a fallback behavior. Otherwise, it would confuse web designers in the fallback situation. So far, we have the following options. 1. Remove ic-height from the spec 2. Use the *average* vertical height as a fallback if “水” is absent as Gecko does. 3. No adjustment if we cannot get a necessary metric from a font, as discussed in #6348. 4. Change the definition of ic-height to something else like ch-height. e.g., `using the advance height of “水”` -> `using the height of “0”` Any other ideas? -- GitHub Notification of comment by shivamidow Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/8792#issuecomment-1536786327 using your GitHub account -- Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config
Received on Friday, 5 May 2023 21:11:53 UTC