Re: [Groff] Underlining, again

[Tadziu Hoffmann]

> As to changing fonts while underlining, it's hard to imagine
> a situation in which it's likely to happen.  Underlining
> should at best be an occasional effect, IMHO.  Still,
> one likes to have solutions that cover every possibility.

Well, for editorial purposes it's sometimes useful to mark
up changes to a document, for example by underlining newly
inserted text and striking through deleted text, and these
have to be available *in addition* to all other markup.

Here's my second attempt, which works a bit better but still
has problems once in a while because grops's output is "too
optimized" (e.g., it sometimes uses "ashow" to produce a space
and can thus occasionally step (invisibly) beyond the end of
the line, but the simple underline algorithm doesn't realize
what grops is doing).  Ultimately I think the only sensible
solution is to make grops itself underline-aware and make
.cu do underlining in troff if not in compatibility mode.


.\"
.\" ----------------------------------------------------------------
.de XX
ps: def
grops begin
/decornone { grops begin /X { } def /Y { } def /y2 -1 def end } def
/decorline { grops begin u neg /uld exch def u /ulw exch def
             /X { currentpoint /y0 exch def /x0 exch def } def
             /Y { currentpoint /y1 exch def /x1 exch def
                  drawline /x2 x1 def /y2 y1 def } def end } def
/drawline { gsave ulw setlinewidth 0 setlinecap x1 y1 uld sub moveto
            y2 y0 eq { x2 y2 } { x0 y0 } ifelse uld sub lineto stroke
            grestore } def
decornone
/uld 0 def
/ulw 0 def
/A { X show Y } def
/B { 0 SC 3 -1 roll X widthshow Y } def
/C { 0 exch X ashow Y } def
/D { 0 exch 0 SC 5 2 roll X awidthshow Y } def
/E { 0 rmoveto X show Y } def
/F { 0 rmoveto 0 SC 3 -1 roll X widthshow Y } def
/G { 0 rmoveto 0 exch X ashow Y } def
/H { 0 rmoveto 0 exch 0 SC 5 2 roll X awidthshow Y } def
/I { 0 exch rmoveto X show Y } def
/J { 0 exch rmoveto 0 SC 3 -1 roll X widthshow Y } def
/K { 0 exch rmoveto 0 exch X ashow Y } def
/L { 0 exch rmoveto 0 exch 0 SC 5 2 roll X awidthshow Y } def
/M { rmoveto X show Y } def
/N { rmoveto 0 SC 3 -1 roll X widthshow Y } def
/O { rmoveto 0 exch X ashow Y } def
/P { rmoveto 0 exch 0 SC 5 2 roll X awidthshow Y } def
/Q { moveto X show Y } def
/R { moveto 0 SC 3 -1 roll X widthshow Y } def
/S { moveto 0 exch X ashow Y } def
/T { moveto 0 exch 0 SC 5 2 roll X awidthshow Y } def
end
..
.de normal
\X'ps: exec decornone'\c
..
.de underline
.ie '\\$1'' .nr _w \\n[.ps]/20
.el         .nr _w \\$1
.ie '\\$2'' .nr _d \\n[.ps]/16
.el         .nr _d \\$2
\X'ps: exec \\n[_w] \\n[_d] decorline'\c
..
.de strikethrough
.ie '\\$1'' .nr _w \\n[.ps]/20
.el         .nr _w \\$1
.ie '\\$2'' .nr _d -\\n[.ps]/4
.el         .nr _d \\$2
\X'ps: exec \\n[_w] \\n[_d] decorline'\c
..
.\" ----------------------------------------------------------------
.sp 3c
.ll 4c
.\" .ps 24
.\" .vs 26
\Y[XX]\c
.strikethrough
The general syntax for writing \fBgroff\fP documents is relatively easy,
but writing extensions to the roff language can be a bit harder.
.normal
The roff language is line-oriented.
.underline
There are only two kinds of lines,
\fIcontrol lines\fP and \fItext lines\fP.
.normal
The control lines start with a \fIcontrol character\fP,
by default a period \(lq.\(rq or a single quote \(lq\^'\^\(rq;
all other lines are text lines.