- From: Alan Stearns <stearns@adobe.com>
- Date: Sun, 8 Feb 2015 02:45:02 +0000
- To: "public-houdini@w3.org" <public-houdini@w3.org>
- CC: John Daggett <jdaggett@mozilla.com>, Bram Stein <stein@adobe.com>
So we’ve resolved to create a spec for a font interface that contains font metrics information necessary [1] for script to produce interesting typographic effects (drop caps, baseline grids, etc.) I have some initial thoughts about how this information should be exposed, and some concern about how we should rationalize what’s currently specified for canvas TextMetrics [2]. There are quite a few metrics we could expose. I don’t know that it’s necessary to include every possible metric in the first cut of this interface. It seems to me that we could start with a reasonable subset and add more information as needed. I think a reasonable subset would include: alphabetic baseline hanging baseline ideographic baseline ascent descent x height cap height Steve warned that there are several different meanings for ‘ascent’ and ‘descent’ in different fonts. So I assume this interface should pick one and describe how to translate known differences to what the interface provides. The TextMetrics interface has attributes for some of these metrics in CSS pixel units. This makes sense for the canvas measurements being made by that interface, but I’m thinking the font interface we’re designing should be expressed in more abstract units. One possibility is to add a unitsPerEm attribute and express all the other metrics in those font-specific units. That’s probably the most natural thing to do for typographers. But I think it could also work to rationalize on a single unitsPerEm value or use an em percentage. Thanks, Alan [1] but not sufficient - used font and rendered baseline position is also needed. [2] https://html.spec.whatwg.org/multipage/scripting.html#textmetrics
Received on Sunday, 8 February 2015 02:45:34 UTC