[MPEG-OTSPEC] Skia-based ot-svg renderer hook to freetype

[Rod Sheeter]

If I'm following correctly
https://gitlab.freedesktop.org/freetype/freetype-demos/-/commit/626b43db566f907fa7b6926705e914259c54b9cf
is working around a bug that results from rsvg taking an svg2
interpretation of width/height. That seems a bit odd as the opentype spec
specifically references http://www.w3.org/TR/SVG11 and the svg documents in
Google-origin ot-svg seem to explicitly indicate that they are in svg 1.1
(<svg ...xmlns... version="1.1">) and thus probably shouldn't be
interpreted using svg 2 conventions.

For context, "Google-origin ot-svg" is likely built by
https://github.com/googlefonts/nanoemoji. Based on a quick glance at some
of our testdata, e.g.
https://github.com/googlefonts/nanoemoji/blob/main/tests/rect_picosvg.ttx,
it looks to me like we followed the examples given in
https://learn.microsoft.com/en-us/typography/opentype/spec/svg#glyph-identifiers
and do not include viewbox or width/height. We assume units to be
interpreted as advised in
https://learn.microsoft.com/en-us/typography/opentype/spec/svg#coordinate-systems-and-glyph-metrics
.

Cheers, Rod S.



On Wed, Jul 5, 2023 at 4:10 PM Hin-Tak Leung <htl10 at users.sourceforge.net>
wrote:

> Okay it says "out-of-memory condition"
> https://gitlab.freedesktop.org/freetype/freetype-demos/-/commit/626b43db566f907fa7b6926705e914259c54b9cf
> instead of "memory exhaustion" (I think that's my subject heading when I
> posted to freetype-devel).
>
> It has my name on it, and is the 3rd most recent commit on freetype2-demos
> (as of now). You didn't look.
>
> On Thursday, 6 July 2023 at 06:43:35 GMT+8, Hin-Tak Leung <
> htl10 at users.sourceforge.net> wrote:
>
>
> Actually Adobe/Mozilla OT-SVG fonts do *not* return EM, EM but something
> like a few hundred, a few hundred.
>
> The bug fix in freetype2-demos I submitted was that, if it comes out as
> 1,1, it means EM, EM (1024, 2048 or there abouts).
>
> Search for "memory exhaustion" in the freetype2-demos commit log, as I
> suggested. It isn't that hard to find.
>
> On Thursday, 6 July 2023 at 06:36:49 GMT+8, Hin-Tak Leung <
> htl10 at users.sourceforge.net> wrote:
>
>
> It is the result from the "intrinsic dimensions" routine - (there is a
> routine of that sort of name in both rsvg and skia). It returns some larger
> numbers, EM,EM I think for Adobe/Mozilla OT-SVG fonts, but 1,1 from rsvg
> and 0,0 from skia for Google-origin OT-SVG fonts.
>
> Clear enough?
>
> On Wednesday, 5 July 2023 at 22:00:54 GMT+8, Cosimo Lupo <
> cosimo at anthrotype.com> wrote:
>
>
> I have no idea what you're talking about. Please, clarify what this
> difference is supposed to be, otherwise this is just spreading rumors.
>
> On Wed, Jul 5, 2023 at 2:33 PM Hin-Tak Leung <htl10 at users.sourceforge.net>
> wrote:
>
>
>
> On Wednesday, 5 July 2023 at 20:49:42 GMT+8, Hin-Tak Leung <
> htl10 at users.sourceforge.net> wrote:
>
>
> > On Wednesday, 5 July 2023 at 03:24:11 GMT+8, Cosimo Lupo <
> cosimo at anthrotype.com> wrote:
>
> > > Hin-Tak, what do you mean by "Google OT-SVG fonts"? They're only one
> OT-SVG format.
>
> > Yes and no. I don't have that many OT-SVG fonts - 3 from Adobe/Mozilla
> sources, and the rest (more than 2 and less than 10) from Google Fonts. The
> two sets behave differently, and get processed by two different code paths
> in freetype2-demos. The Google set triggers the memory exhaustion bug I
> fixed in freetype2-demos about a month ago; the Adobe/Mozilla set does not.
>
> > That was all part of the activities around the time with the Google font
> SVG subsetting bug. Look at the freetype2-demo log around the same time you
> investigated and fixed the subletting bug.
>
> Actually having looked at Skia and skia-python's SVG related functionality
> last night, Skia also follows two slightly different code paths for the two
> "types" of OT-SVG fonts. There will be a small "if x else ..." clause
> separating the two in Skia related code, if /when I finish.
>
>
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