Re: [Indic-computing-devel] NCST IndiX examined

[<jk...@Fr...>]

Dear Keyur,

Welcome!

ks> Err! Please carefully see the source code of xc/lib/X11/QuTextExt.c
ks> in original XFree86. It also first converts the string into UCS-2
ks> before sending request to the X Server. The only difference between
ks> the conversion is that, originally X Server pads an extra byte to
ks> each element of the string to make it UCS-2. We assume incoming
ks> sequence into UTF-8 and convert it into UCS-2. The changes made in
ks> IndiX was earlier breaking relationship with other foreign languages
ks> like French, German (all with iso-8859-* encoding). But now I am
ks> taking care of this also.

I don't see anything specific to Unicode or UCS-2 in this file.

   http://cvsweb.xfree86.org/cvsweb/xc/lib/X11/QuTextExt.c?rev=1.4&content-type=text/x-cvsweb-markup

There is only one [QueryTextExtents] protocol request in the X11
protocol.  This request is used for both the `XQueryTextExtents16()'
and `XQueryTextExtents()'.  It expects 2 byte glyph indices.

For "linear" (single byte) glyph indices, the X library makes the MSB
of each 2 byte glyph index to be zero (i.e. linear encodings are
treated as row 0 of a 2-D glyph matrix).  All this is explained in the
X Protocol specification.  [See Page 37, QueryTextExtents]

Compare:

   http://cvsweb.xfree86.org/cvsweb/xc/lib/X11/QuTextE16.c?rev=1.4&content-type=text/x-cvsweb-markup

ks> X11 text drawing calls accepts character codes and send them to the
ks> X Server along with other data in the form of a request. We have not
ks> changed this semantic. This character codes are then used by the
ks> subsequent font library to get the glyph codes.

ks> In my view, it is compatible with the X Window System protocol.

You seem to have ignored the part of the X protocol specification
(that I had quoted in my review) that explicitly states that the X
protocol DOES NOT deal with character codes and that the clients just
use indices into the glyph array.

    ``Font: A font is a matrix of glyphs (typically characters).  The
      protocol does no translations or interpretation of character
      sets.  The client simply indicates values used to index the
      glyph array.  A font contains additional metric information to
      determine interglyph and interline spacing.'
          
    X Protocol Specification, Glossary, pp 154.

If you want to see the effect of your changes on protocol compliance,
you could:

    (a) run the X protocol test suite.  In particular,

        /tset/CH06/drwimgstr16/Test{all}
                ... and others in this section ...
        /tset/XPROTO/imgtxt16/Test{all}
        /tset/XPROTO/plytxt16/Test{all}
        /tset/XPROTO/qrytxtextn/Test{all}
        
    (b) attempt to view cryllic, korean or japanese text (i.e
        character encodings whose code points fall outside the
        US-ASCII range)

You are probably the best placed in our group of developers to talk
about the technology behind Indic script rendering.  I am looking
forward to learning from your experience.  Do you have tutorial or
writeup on Indic rendering that you could share with this group?

Regards,
Koshy
<jk...@fr...>