Re: ACTION-2932: Check with patrick about whether IE ran against the latest version of the test (SVG Working Group)

Hi Cam,

--Original Message--:
>Alex Danilo:
>> One more useful reference section:
>> 
>> http://www.w3.org/TR/xsl/#area-alignment
>> 
>> describes the aligment of the various baselines in more detail for
>> mixed scripts.
>
>Also http://dev.w3.org/csswg/css3-linebox/#baseline and
>http://dev.w3.org/csswg/css3-linebox/#BaselineUsage which I think are
>adaptations of the XSL spec text.
>
>I’d like to know whether anyone agrees with my analysis posted here:
>
>  http://lists.w3.org/Archives/Public/public-svg-wg/2011JanMar/0054.html

Most of the analysis is good. Text layout is so simple, isn't it...

Anyway, the first bit about using the alphabetic baseline is
correct but the first image is not. What is happening in the
test is that there is a mixing of different font sizes. So even though
the alphabetic baseline is being used for alignment, when the font
shrinks, the new set of baselines does not.

So the hanging baseline is still at the height of the start of the
text being aligned, namely at the large font size. That's why
the full test now has a horizontal line drawn where the hanging
baseline is for the entire line.

The small Devanagari glyph cannot align to the alphabetic
baseline, since it's not authored that way, so it hangs under the
hanging baseline which is up at the top, and results in the image
you have  at the end of the post.

Regarding the text-script property, SVG has no such property
to explicitly set it. However, UAX#24 describes the mapping of
Unicode points to script names which can be used to derive
the preferred baseline based on the writing system.

There used to be a really good picture of the alignment with
different sizes in an old FO draft but I can't find it.

However, fundamentally the largest font on a line defines the
positioning of the baseline set (not always) in the same way
that the largest font on a line with a single baseline defines
the baseline/ascent/descent. As font size changes, the only
movement of the baselines is to move them further apart,
they never contract or glyphs won't align along the line.
So, we get the result as shown in the last image which
you correctly identified as the expected behaviour.

In additon, SVG saying 'auto' means use UAX#24 or similar
to work out what the initial value for the script should be,
and that may mean scanning forward until you have a
meaningful character to identify that, i.e. not white-space
or neutral, etc. etc.

Alex

>-- 
>Cameron McCormack ≝ http://mcc.id.au/
>
>

Received on Friday, 28 January 2011 01:12:12 UTC