[Pkg-fonts-bugs] Bug#358526: ttf-freefont: problem if letters "s" and "t" are combined when freemono is used

[Jan Willem Stumpel]

This bug occurs in Firefox 1.5.0.2 (not in Mozilla 1.7.12), and in
programs which use the latest version of Pango (e.g. the print
program paps, http://paps.sourceforge.net/). It does not only
occur with the st combination; also in other cases single-width
ligatures are substituted for letter combinations (ff, fi, fl).
This looks weird in a print-out which should be monospaced (like
source code text). It is specially weird with st because the st
"ligature" in FreeMono is in fact only "t".

Other monospaced fonts (like Courier, Courier New) also have
ligatures (in the Unicode block "Alphabetic Presentation Forms",
beginning at U+FB00), but Pango does not substitute them
automatically. It seems that in FreeMono, the ligatures are
encoded in a way that says "use me whenever you can" (they are in
FreeMono's "GSUB" table), while in the other fonts these ligatures
say "use me only when asked for explicitly" (I could not find them
in the Courier New GSUB table). So it seems to be a bug in
Freemono alright. I suppose the bug has been there for ages but
only Pango 1.12, which started to pay (more?) attention to
substitutions, has revealed it.

This makes Freemono unusable (in practice) for monospaced
printing. But it would, I suppose, be a fairly simple matter to
remove these "Alphabetic Presentation Forms" from the freefont
GSUB tables if you understand the syntax of these tables (which I
do not).

Regards, Jan