Re: [font-metrics-api] font data versus typographic layout results

On 7/30/15, 7:15 AM, "Peter Krautzberger" <peter.krautzberger@mathjax.org>
wrote:

>Hi Alan,
>
>
>It looks like this would provide some global font metrics, but not the
>metrics of individual characters/strings. Is that correct?
>
>
>That would be helpful, particularly the baseline information, but it
>would not be sufficient for a use case like mathematical layout.

Not global - it’s giving the results from the first line box. But you are
correct, this would not be sufficient for mathematical layout. It’s a step
towards what you need, satisfying simpler use cases.

>
>
>
>Best regards,
>Peter.
>
>
>On Wed, Jul 29, 2015 at 3:02 AM, Alan Stearns
><stearns@adobe.com> wrote:
>
>Hey all,
>
>I initially thought that exposing raw font data would be the right first
>step for finding a way to correctly polyfill initial-letter, line grid,
>etc. Conversations I’ve had since the last Houdini meeting have moved me
>towards John Daggett’s point of view, that exposing the typographic
>*results* of line boxes is a better stepping-stone. Getting those results
>and making small changes is better than trying to reverse-engineer what
>the browser is doing with the raw font data.
>
>The box tree API currently talks about DeadFragmentInformation, which
>gives you a basic geometry result. My current thinking is that there
>should be a way to get more fine-grained typographic information within
>that basic geometry. It might look like:
>
>interface DeadFontMetrics {
>        readonly attribute double baseline;
>        readonly attribute double alphabeticBaseline;
>        readonly attribute double ideographicBaseline;
>        readonly attribute double ascent;
>        readonly attribute double descent;
>        readonly attribute double xHeight;
>        readonly attribute double capHeight;
>}
>
>
>partial interface DeadFragmentInformation {
>        Promise<DeadFontMetrics> getFontMetrics();
>};
>
>
>Where the DeadFontMetrics attributes give you the relevant typographic
>position of the first in-flow line box in pixels from the top of the
>fragment.
>
>An interesting idea is that we could work on the box tree and font metrics
>in parallel by adding getFontMetrics() to Element as well, which would
>give you the same typographic positions of the first in-flow line box from
>the element’s top. This might be sufficient to polyfill initial-letter and
>flexbox’s align-items:baseline. Something more complicated like line-grid
>would need to wait for more of the box tree to be exposed.
>
>Thanks,
>
>Alan
>
>
>
>
>
>
>

Received on Thursday, 30 July 2015 14:23:40 UTC