RE: Generic base characters

From: Peter Constable (
Date: Sun Jul 15 2007 - 00:14:03 CDT

  • Next message: Philippe Verdy: "RE: Generic base characters"

    From: [] 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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