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Re: A definition for "character cell" is not provide in the spec

From: Doug Schepers <doug.schepers@vectoreal.com>
Date: Wed, 07 Feb 2007 16:20:34 -0500
Message-ID: <45CA42A2.2070609@vectoreal.com>
To: Jonathan Watt <jwatt@jwatt.org>, www-svg@w3.org

Hi, Jonathan-

I'm always interested in comments that allow me, as an author, to have 
reliable interoperability between browsers.  Thanks for bringing this up.

I'm pretty sure we cover this in the SVG 1.1 spec (although we normally 
describe it in terms of bounding boxes rather than glyph cells).  It's 
kind of scattered throughout the spec, but it's perhaps most explicit 
here [1].

We take it a step further in SVG Tiny 1.2, where we unify and clarify 
the various discussions of bounding box [3], and we add the 
pointer-event value 'boundingBox' [4].

This does not allow authors to use the "complete" bbox for text 
elements, but it does do so for textArea.  If you think this is still 
unclear, or if you don't think the functionality will suffice, we could 
add it as an errata item.

[1] http://www.w3.org/TR/SVG11/text.html#ObjectBoundingBoxUnitsTextObjects
[2] http://www.w3.org/TR/SVG11/text.html#TextSelection
[3] http://www.w3.org/TR/SVGMobile12/intro.html#TermBoundingBox
[4] http://www.w3.org/TR/SVGMobile12/interact.html#PointerEventsProperty


Regards-
-Doug

Research and Standards Engineer
6th Sense Analytics
www.6thsenseanalytics.com
mobile: 919.824.5482

Jonathan Watt wrote:
> 
> Dear SVG WG,
> 
> SVG implementations seem to have diverged due to a lack of a definition 
> for the term "character cell" which is used in:
> 
>   http://www.w3.org/TR/SVG11/interact.html#PointerEventsProperty
> 
> Mozilla defines this to be the rectangle that exactly fits to the edges 
> of the painted area of each glyph. This might make sense in the case of 
> text along a path or where each glyph is positioned individually, but in 
> the case of a run of text along a straight line (without any extra 
> character spacing) it leads to hit-test gaps between glyphs. Other 
> implementations seem to use a larger box so they don't have these gaps. 
> Perhaps they simply decide to use a single box around runs of text along 
> a straight line? Or maybe they define "character cell" to be the box 
> that is the advance of the glyph in question wide, by the largest font 
> ascent to largest font decent high? (Details from other implementers 
> would be welcome.)
> 
> At any rate, please define the term "character cell" so that 
> implementors can eliminate this difference between their implementations.
> 
> Regards,
> Jonathan
> 
> 
Received on Wednesday, 7 February 2007 21:20:52 GMT

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