[css-writing-modes] baseline tables figures are confusing, do not correspond to OTF BASE table

[macnmm]

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

https://www.w3.org/TR/css-writing-modes-3/images/baselines.gif

Both of these images do not convey a usable embox top or bottom baseline that is the normal line top and bottom for CJK text. The embox top and bottom can be obtained from the 'ideo' baseline and the point size of OpenType fonts' BASE table. These are the preferred measuring points for typographic line top and bottom, and leading measurements for CJK text. They are also the alignment points to be used with text grids and in mixed sized text.

[fantasai]

Heh. These figures are ancient, they were assembled before I even joined the CSSWG. :P @dauwhe Can you help?

[dauwhe]

Here's a sketch as I'm trying to figure out what's going on

@macnmm, so we'd set the ideographic baseline to -120 because of the IDEO baseline value from the metrics, and then add 1000 to that to get the embox top? In this case that matches all the ascent values, but that doesn't appear to be true all the time.

I have some CJK fonts where ascent + descent does not equal the units per em (Arial Unicode MS), but I haven't found one with a base table yet.

[dauwhe]

Here's a font where text-top and text-bottom seem distinct from ideographic top and ideographic bottom.

[frivoal]

@dauwhe Have you been able to make a figure you're happy with?

[dauwhe]

@dauwhe Have you been able to make a figure you're happy with?

The goal was to make a figure @macnmm is happy with :)