From: Kent Karlsson (firstname.lastname@example.org)
Date: Mon Jul 16 2007 - 13:50:52 CDT
Asmus Freytag wrote:
> > 1) I'm not so sure about that. It's better to have a single defined
> > behaviour (assuming the characters in question are at all supported).
> In cases like this, you not only have the question of which
> are supported, but also which *character sequences* are
> supported. Just
> like a font designed for some language other than Swedish
> might have a
> glyph for the f, and the j, but, which despite supporting an
> fi and fl
> ligature does not support an fj liagature, other parts of the layout
> system may legitimately not support some sequences even if
> they support
> each letter and similar sequences.
While I would appreciate if more fonts supported the fj ligature,
I would expect no rendering system or font to insert a dotted
circle between an f followed by a j just because they don't
support that ligature. Instead they just output an f followed
by a j, though the result sometimes is not perfect (but much
better than getting a dotted circle in-between).
> This is not a conformance issue but
> one of quality and scope of an implementation.
True. But, while formally conforming, it is still a bad idea
to start inserting dotted circles where there is none in the input.
> > 2) NBSP base is for sequences of combining characters preceeded
> > by beginning of string or by a control char. I think using NBSP
> > as the implicit base in such cases is a reasonable behaviour.
> > (Inserting a dotted circle is not.)
> I've always understood that recommendation to be aimed a
> preventing the
> combining mark from being handled in completely weird ways, e.g. by
> trying to overhang it into empty space at the beginning of a
> line. I see
I would say that trying to overhang it into empty space at the
beginning of a line is much LESS weird than getting a dotted cirlce
there (where none was in the text).
> nothing in the standard that prevents a higher level
> protocol, such as Uniscribe, to override this behavior.
Formally, no, but it is still a bad idea.
> > 3) This thread started talking about there actually being a base
> > present in the text just before the combining sequence, just that
> > the base was in another script (or some symbol/punctuation).
> > That is not an error case from a text rendering point of view.
> > There is no reason to start inserting dotted circle, NBSP,
> > or anything else. Ligation, kerning, postioning adjustments
> > are unlikely to work except for special cases, but some rough
> > approximate (assuming again that the individual characters at
> > all are supported by the rendering system and font used) should
> > be output.
> As I have pointed out, I regard the application of the policy
> to these
> cases as one of the 'issues', because it can lead to unintended (and
> limiting) results.
> But I can understand why layout engine creators don't
> want to support an anything goes approach, because doing that
> at *high quality* is extremely expensive.
Yes, but *high quality* for the unexpected cases was not required.
Just that one got a reasonable approximation; dotted-circle-less.
> That said, a better way to do the
> fallback would be appropriate. Johns suggested list of
> generic bases is
> a good way to indicate a minimal level of support.
I agree, for getting better-quality display, but there is still
no reason to insert dotted circles for other cases.
> >> Authors should not have
> >> an expectation of portably exchanging buggy text with perfect
> A buggy text is one that has missing base characters. That's
> how I meant
> this usage in my post. If you construed that differently
> based on some
> real or perceived deficiency in how I worded that, I'm sorry.
I did not. But that was not the case that this thread was mostly
> But also, indicating that a renderer can't support something, *is*
> legitimately the business of the implementation. I think that
> that uses fallbacks for diacritics and that can't rais stacked
> diacritics properly would be better off causing a visible
> clash or even
> spacing the combining marks than silently overstriking them.
> As another example.
That would be better than inserting spurious dotted circles.
This archive was generated by hypermail 2.1.5 : Mon Jul 16 2007 - 13:52:00 CDT