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

Thanks for clarifying, Alan! It would definitely be a helpful step.

Peter.

On Thu, Jul 30, 2015 at 4:23 PM, Alan Stearns <stearns@adobe.com> wrote:

> 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
> >
> >
> >
> >
> >
> >
> >
>
>
>