Re: glyphs, characters and fonts

[Haisam Ido <haisam at ido dot org>]

Wow!  Thank you Chahine.  Perhaps this can be placed in a FAQ?

Quoting \"Chahine M. Hamila\" <mch at chaham dot com>:

> Salaam,
> 
> A character encoding is the way a character is internally encoded,
> ISO-8859-1, ISO-8859-6, CP-1256, Unicode encodings etc...
> 
> For example, let\'s suppose we are using an encoding called AE where s
> is
> in position 50, l in position 55 and m in position 60.
> The string slm (salaam) would be
> char *str = [50, 55, 60,0]; // The 0 being the mark of end of string in
> C
> i.e. str[0]==50, str[1]==55, etc..
> 
> The glyph is the drawing that appears on a screen.
> For example, if we decide we associate the drawing \"s\" to the position
> 50 in the encoding AE, \"l\" to the position 55 and \"m\" to the position
> 60, the string slm would appear on the screen as \"slm\".
> But if we decide we associate the drawing \"a\" to the position 50 in the
> encoding AE, \"c\" to the position 55 and \"e\" to the position 60, the
> string slm would appear on the screen as \"ace\" BUT WOULD STILL MEAN slm
> TO THE COMPUTER!!!
> 
> A font file is in general a file where these drawings are stored at
> given positions.
> Where it\'s easy to make the match between the encoding and the
> drawing\'s
> position (Latin, Hebrew, Russian, etc...) the drawings, better known as
> the glyphs, are stored at the same location their encoding indicate,
> thus making the mapping trivial. For example, the latin glyph \"A\" will
> be stored at position 65 in a font file, like the ISO-8859-1 or most
> other encodings locate the letter A.
> In Arabic (except if you chose to use my experimental position agnostic
> glyphs \"Square Arabic\" in Akka;)), we have shaping, which means, the
> same encoding will not necessarily correspond to the same glyph and we
> have to go through a more complex processing. For example, we could
> decide that AE\'s s, i.e. the char with the code 50 would be associated
> with the first position glyph stored at the element 10 in the glyph
> file, mid position in position 11, end position in element 12, and lone
> position in element 13, and the soft would chose what is the
> appropriate
> glyph to display according to the context. For that reason, it is not
> important where glyphs are stored in a file as long as the soft knows
> where they are, but it is important to use standard encodings because
> files, libraries for string manipulations and other data treatment
> pieces of codes rely on the encoding.
> 
> We might wonder why we don\'t simply make an Arabic encoding using
> directly a trivial code-to-glyph encoding (or use the trivial upper
> Forms maps in unicode\'s tables). Because that would mean making the
> problem harder, moving it in the layer of every data manipulation where
> the same letters would be considered different according to their
> position or context, and thus making a trivial comparison of mid-word s
> and end word s a complex work for example.
> 
> Hope that makes it clearer.
> Salaam,
> Chahine
> 
> \"Haisam K. Ido\" a *crit :
> 
> > Hi Guys:
> >
> > Is there a document which describes the meanings and relationships
> > between glyphs, characters and fonts?
> 
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