RE: SVG in OpenType proposal

After doing a bit more research, I realized that I was wrong. 
PDF stores the widths of each glyph in a separate dictionary entry and uses that to place the glyph.

Maybe having a different bbox for a particular SVG glyph is ok and we should have an internal discussion on how this can fit into our model.
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From: rocallahan@gmail.com [rocallahan@gmail.com] On Behalf Of Robert O'Callahan [robert@ocallahan.org]
Sent: Wednesday, February 06, 2013 5:01 PM
To: Rik Cabanier
Cc: public-svgopentype@w3.org; Leonard Rosenthol; Cameron McCormack
Subject: Re: SVG in OpenType proposal

On Thu, Feb 7, 2013 at 1:44 PM, Rik Cabanier <cabanier@adobe.com<mailto:cabanier@adobe.com>> wrote:
Robert O'Callahan wrote:
> I don't think so. AFAIK glyph bounding-boxes, unlike other text metrics, don't affect shaping. (I hope
> we're talking about the same thing here: by bounding-box I mean a rectangle that encloses everything
> drawn for a glyph.) In Gecko we only use them to optimize painting by ignoring text that doesn't intersect
> the area to be painted. (Except for a very special case involving MathML layout that is not relevant here.)
> There is no particular reason why glyph bounding-boxes need to be constant over time; bounding boxes for
> other kinds of content are not constant over time.

In PDF, the width of the bounding box influences where the next glyph will start.

That seems odd. I would have expected it to rely on advance widths.

So, if you have different sized glyphs between the OpenType and SVG representations, text will come out misaligned.

Text layout should depend only on existing OpenType tables, so a PDF viewer that wants to support SVG glyphs should use the OpenType bounding boxes for text layout. Since PDFs usually aren't dynamic, the true ink bounding box probably isn't even relevant to a PDF viewer.

Rob
--
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Received on Thursday, 7 February 2013 01:39:40 UTC