Re: Macrons

From: John Hudson (
Date: Tue Apr 05 2005 - 16:48:41 CST

  • Next message: Mark E. Shoulson: "Re: Macrons"

    Peter Constable wrote:

    >>>I find to my surprise that the Doulos SIL trick (if I can call it
    > that)
    >>It's not a "trick", it's a simple OpenType feature: ccmp.

    > A slight correction: I think you'll find it's the 'mark' feature.

    Indeed. To clarify for non font folk:

    <ccmp> is an OpenType Layout substitution (GSUB) feature that maps from multiple
    characters to individual, precomposed glyphs (it can also be used to map individual
    characters to multiple glyphs, but that is another topic), and which is useful if you have
    a such precomposed glyphs in a font. [Note that if the precomposed glyphs correspond to
    precomposed character combinations in Unicode, e.g. A with macron, you don't need to use
    <ccmp>, because you can map directly to the Unicode value and allow system or application
    software to figure out the character level decompositions; the feature is for accessing
    precomposed glyphs that are not separately encoding in Unicode, e.g. W with macron.]

    <mark> is an OpenType Layout positioning (GPOS) feature that uses anchors to position
    marks relative to base glyphs, e.g. to position a macron over a W. The positioning is done
    on the fly during rendering. It has the advantage over the <ccmp> approach of being more
    efficient in terms of font size, requiring fewer glyphs, but is less efficient in terms of
    processing speed.

    A font may implement a combination of both glyph substitution and mark positioning.

    Adam, understandably, has created a tutorial on how to implement the <ccmp> feature using
    FontLab, because FontLab does not currently support mark positioning lookups. To implement
    the <mark> feature, one needs to use MS VOLT, which is why it is the OTL tool of choice
    for complex script developers.

    John Hudson

    Tiro Typeworks
    Vancouver, BC
    Currently reading:
    A century of philosophy, by Hans Georg Gadamer
    David Jones: artist and poet, ed. Paul Hills

    This archive was generated by hypermail 2.1.5 : Tue Apr 05 2005 - 16:50:21 CST