🚀 go-pugleaf

   A subscript dot is used by the International Phonetic Association to indicate
   a retracted pronunciation. Is there a way to centre the dot with respect
   to the letter it is below by replacing the h'-0.3m' constant below with
   something which is equal in value to half of the width of the preceding
   character?

   ...
   Adapted from James Clark's version of the -me macros' .ds for , (cedilla):

   .ds . \k_\h'-0.3m'\v'.22m'\*(#[.\v'-.22m'\h'|\\n_u'
   .sz 16
   This is a test of the s\*. t\*. r\*. n\*. retroflex in groff.

The definition of `,' in the groff -me macros is

  .ds , \k_\h'-(\\n(.wu)',\h'|\\n_u'

`\n(.w' gives the width of the previous character.

If you want to center the dot under the previous character a suitable
definition would be:

  .ds . \k_\h'-\\n(.wu-\w'.'u/2u'\v'.25m'.\v'-.25m'\h'|\\n_u'

The groff \Z escape sequence is quite convenient here, allowing this
to be written as:

  .ds . \Z'\h'-\\n(.wu-\w'.'u/2u'\v'.25m'.'

This has the deficiency that it will fail if it's used in a macro
argument (because \n(.w gets expanded too soon).  The groff \E escape
sequence allows this problem to be avoided:

  .ds . \Z'\h'-\En(.wu-\w'.'u/2u'\v'.25m'.'

The other problem is that something like `y\*.' won't work.  This
can be fixed using the \n[.cdp] register.  Using this gives:

  .ds . \Z'\h'-\En(.wu-\w'.'u/2u'\v'.25m+\En[.cdp]u'.'

This definition still doesn't work as well as it might for italic
fonts.

James Clark
jjc@jclark.com