Branden Your \D description looks good, except perhaps for the word "solid", which I suppose was to avoid overloading "fill". But "fill" is baked into pic, from which I suspect the vast majority of \Ds originate. It's also PostScript terminology.
I wrote the raster ellipse-drawing program for plan 9. Its arc capability was not adopted because the interface was sufficiently ugly that calling it was comparable to writing a trivial floating-point ellipse program from scratch. The main issue is that the endpoints of an arc are hard to specify on a raster. Since groff doesn't know about rasters, perhaps that decision could be revisited. Do you have a good candidate for an interface? Tilted ellipses pose another problem--specification. This difficulty is exaggerated on a raster, where giving two half axes is questionable, because in general roundoff results in non-perpendicular axes, Perhaps the cleanest spec in this setting is to give a bounding box and two points of tangency, but this may not be popular. Again, groff might enable other possibilities. Doug On Tue, Jun 6, 2023 at 4:07 PM G. Branden Robinson <g.branden.robin...@gmail.com> wrote: > > [self-follow-up] > > At 2023-06-05T20:57:37-0500, G. Branden Robinson wrote: > > Hi Doug, > > > > At 2023-06-05T19:48:50-0400, Douglas McIlroy wrote: > > > > I understand that groff has the \D escape which allows you, among > > > > other things, to draw outline and filled polygons. > > > > > > Very helpful. I rely on the old testament book of Ossanna and on > > > groff(7), neither of which cover that option for \D. One must look > > > in "info groff". I hope Branden's extensive edits to groff(7) for > > > 1.23 may correct my myopia. > > > > Regrettably, not yet. I've been kicking that can down the road [...] > > Here's my first cut of this. > > Drawing commands > Drawing commands direct the output device to render geometrical > objects rather than glyphs. Specific devices may support only a > subset, or may feature additional ones; consult the man page for the > output driver in use. Terminal devices in particular implement > almost none. > > Rendering starts at the drawing position; when finished, the drawing > position is left at the rightmost point of the object, even for > closed figures, except where noted. GNU troff draws objects with > the selected stroke color; the interior of solid ones is shaded with > the fill color. See section "Colors" above. Coordinates h and v > are horizontal and vertical motions relative to the drawing position > or previous point in the command. > > \D'~ h1 v1 ... hn vn' > Draw B-spline to each point in sequence, leaving drawing > position at (hn, vn). > \D'a hc hv h v' > Draw circular arc centered at (hc, vc) from the drawing position > to (h, v). > \D'c d' > Draw circle of diameter d with its leftmost point at the drawing > position. > \D'C d' > As \D'C', but the circle is solid. > \D'e h v' > Draw ellipse of diameter d with its leftmost point at the > drawing position. > \D'E h v' > As \D'e', but the ellipse is solid. > \D'l h v' > Draw line from the drawing position to (h, v). > \D'p h1 v1 ... hn vn' > Draw polygon with vertices at drawing position and each point in > sequence. GNU troff closes the polygon by drawing a line from > (hn, vn) back to the initial drawing position. Afterward, the > drawing position is left at (hn, vn). > \D'P h1 v1 ... hn vn' > As \D'p', but the polygon is solid. > \D't n' > Set line thickness of geometric objects to to n basic units. A > zero n selects the minimal supported thickness. A negative n > selects a thickness proportional to the type size; this is the > default. > > Comments? > > How was one supposed to draw a "skewed" ellipse in AT&T troff? That is, > one with its axes rotated non-orthogonally? > > Was any consideration given to elliptical arcs? (Maybe there is a > straightforward transformation of these to B-splines. I don't feel I > understand B-splines very well.) > > Regards, > Branden
