Re: Questions about viewport and metrics

Doug,

Just a quick note for now (I'm at a conference): the latest version of the SVG-in-OpenType spec is at https://groups.yahoo.com/neo/groups/mpeg-OTspec/conversations/messages/1276 (Vlad please correct me if I'm wrong, or if there's a better place for folks to find this). The two docs you point to are initial proposals and definitely out of date. If you have difficulty accessing the latest version above, I'm happy to email it to you for now.

Your ligature flags project utilizing public-domain SVG images is an interesting use case, and I hope the community on this list is able to quickly figure out what's going on.

Sairus

From: Doug Felt <dougfelt@google.com<mailto:dougfelt@google.com>>
Date: Wednesday, February 25, 2015 at 5:34 PM
To: "public-svgopentype@w3.org<mailto:public-svgopentype@w3.org>" <public-svgopentype@w3.org<mailto:public-svgopentype@w3.org>>
Cc: Behdad Esfahbod <behdad@google.com<mailto:behdad@google.com>>
Subject: Re: Questions about viewport and metrics
Resent-From: "public-svgopentype@w3.org<mailto:public-svgopentype@w3.org>" <public-svgopentype@w3.org<mailto:public-svgopentype@w3.org>>
Resent-Date: Wednesday, February 25, 2015 at 5:35 PM

I'm also finding that I can't set a clip-path.  Not sure if this is because clipping isn't supported in this context, or because having the clipPath be a descendant of the referencing svg element isn't supported in this context, or what. It works standalone.

On Mon, Feb 23, 2015 at 1:21 PM, Doug Felt <dougfelt@google.com<mailto:dougfelt@google.com>> wrote:
I'm noticing some behavior with svg opentype in Firefox that I don't fully understand.

The default viewport seems to be 1000x1000 font units. This is mentioned here https://wiki.mozilla.org/SVGOpenTypeFonts#Structure_of_the_SVG_Document but not here http://www.w3.org/2013/10/SVG_in_OpenType/. The latter document leaves it unspecified what the default viewport is, which seems like a problem.

I'm finding that distances in percent will map '100%' to 1000 font units.  The only way I have found to change how lengths in % behave is by changing the transform attribute on the svg element. Specifying a viewBox scales to the 1000x1000 font unit square, and while values without units scale, values in % remain unaffected.  Without a viewBox, specifying width and height attributes on the svg effectively does the same thing as a viewBox of '0 0 width height' (with a viewBox it appears width and height are ignored).  With a font using 2048 upem, if I set transform="translate(0, -ascent) scale(2.048)" I get behavior more in line with what I expected, 100% maps to 2048 font units.  But really what I'd expect is that width and height attributes on the svg element define the view portsize in upem.  It seems a more straightforward way for me to indicate what 100% means.

The 2013/10 document also doesn't say what happens to measurements in other units (em, px, cm...).  Are the units ignored? Disallowed? Is behavior unspecified? Does '1em' map to the font's upem? It would help if the spec were a bit more explicit about these issues.

The way I stumbled across this is by trying to build a font using public-domain SVG images of country flags (from wikipedia) and mapping them to ligatures built from unicode regional indicator symbols.  The SVG's all render fine standalone, but as glyphs they behave very differently depending on the units their drawing commands use. Some are fine, some are too large or too small, and some have a mixture of units and render inconsistently. I was having difficulty using the public spec to resolve this.




--

Doug Felt |      Software Engineer |     dougfelt@google.com<https://mail.google.com/mail/?view=cm&fs=1&tf=1&to=dougfelt@google.com> |   1-650-253-2089