Re: Questions about viewport and metrics

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> 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