>>>> "as" == "Arun Sharma", "keithp" == "Keith Packard"
as> Do you think interpreting the argument to XDrawString()
as> as a sequence of character codes instead of a glyph string would be a
as> violation of the X protocol ?
keithp> Yes. The protocol specification says that the glyphs are
keithp> directly indexed by the character codes delivered over the wire.
as> Yes to bad idea or Yes to illegal (i.e. violation of the protocol) ?
Both.
The X protocol is not specified in terms of code points of character
sets.
Further, it is a bad idea to move code point rendering into the X
server, because the process of rendering code points into visible
artifacts is, in general, application dependent.
as> Is it fair to say that the X protocol doesn't interpret those values (as
as> either character codes or glyph codes) and just uses them as "numbers"
as> used to index a font file ?
Isn't the phrase "directly indexed" clear enough?
The X specification says that its fonts are conceptually arrays of
glyphs and the values specified in the text drawing requests are used
to index into this array.
You can have a linear (one byte index) or two-dimensional index.
Given a glyph index, the glyph retrieval operation can be expressed
as:
one_glyph's_bits = glyph_table_of_font(one-glyph-index)
The important points here are:
o An implementation needs to ensure that a given glyph index into a font
always selects the same glyph (i.e no context sensitivity allowed).
o An implementation is not allowed to substitute a sequence of glyphs
with another (i.e no ligatures).
o An implementation is not allowed to reorder glyphs (as would be needed
when rendering some indic scripts).
o An implementation is not allowed to place glyphs at anything other
than the /precise/ positions in the request (i.e. no kerning).
There seems to be a lot of exciting font-related development happening
in the XFree86 tree (I last looked nearly a decade ago). However, to
my understanding, the requirements of the core protocol have remained
unchanged.
Regards,
Koshy
<[EMAIL PROTECTED]>
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