Re: script or block detection needed for Unicode fonts

From: John H. Jenkins (
Date: Sun Sep 29 2002 - 10:12:45 EDT

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    On Saturday, September 28, 2002, at 03:19 PM, David Starner wrote:

    > On Sat, Sep 28, 2002 at 01:19:58PM -0700, Murray Sargent wrote:
    >> Michael Everson said:
    >>> I don't understand why a particular bit has to be set in
    >>> some table. Why can't the OS just accept what's in the font?
    >> The main reason is performance. If an application has to check the
    >> font
    >> cmap for every character in a file, it slows down reading the file.
    > Try, for example, opening a file for which you have no font coverage in
    > Mozilla on Linux. It will open every font on the system looking for the
    > missing characters, and it will take quite a while, accompanied by much
    > disk thrashing to find they aren't there.

    This just seems wildly inefficient to me, but then I'm coming from an
    OS where this isn't done. The app doesn't keep track of whether or not
    a particular font can draw a particular character; that's handled at
    display time. If a particular font doesn't handle a particular
    character, then a fallback mechanism is invoked by the system, which
    caches the necessary data. I really don't see why an application needs
    to check every character as it reads in a file to make sure it can be
    drawn with the set font.

    John H. Jenkins

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