From: Peter Constable (firstname.lastname@example.org)
Date: Sun Jul 15 2007 - 00:14:03 CDT
From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Christopher Fynn
> The Microsoft OpenType shaping engine, Uniscribe, seems to
> automatically insert a dotted circle as a base character
> for isolated combining marks - and this behavior is outside
> of the control of the font developer.
> IMO it would be much better if font developers were
> responsible for defining their own sets of these base glyphs
> for combining marks - including the base for isolated
> combining marks - and their own lookups for rendering the
> resulting combinations.
Uniscribe inserts a dotted circle glyph only when the author has not included a valid base character for the mark. Font developers are always responsible for their own lookups for rendering a mark glyph on a base. But there's nothing the font developer can do about the scenario in which an author fails to include a base.
Perhaps you have in mind that a font developer should control what glyph is used in that situation, but I see a need, on the assumption that authors should, and normally are, explicitly intentional about what is in their document, and that Uniscribe's fallback rendering is just that: a fallback.
> As base glyphs one might want to include the dotted circle;
> non-breaking space or fixed width spaces such as em space or
> en space;
Unicode specifies that combining marks in isolation -- with no visible base -- should be combined with NO-BREAK SPACE, not any of the other space characters in the standard.
> Right now if I have a lookup in an OpenType font to place
> an isolated mark on the dotted circle Uniscribe also inserts
> dotted circle and I end up getting two doted circles...
> Not all OpenType shaping engines exhibhit this behaviour.
A bug, which can be looked at.
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