Re: RFC: dashtype, aka separate control of line property descibing the dot-dash pattern

[Tait <gnu...@t4...>]

sfeam said (on 2014/03/10):
> On Sunday, 09 March 2014 11:49:09 PM Juhász Péter wrote:
> > ...
> > So there would be a new line property "dashtype" or "dt", allowed
> > everywhere a line specification is accepted.
> > ...
> > So e.g. "plot for [i=0:10] i*x" would do exactly the same as before.
> > But "plot for [i=0:10] i*x" dashtype 1 would keep the line pattern the
> > same for all plotted lines while still cycling the color ...
> > 
> Sort of.  I think I would typically define all the linetypes to default
> to solid, which I suppose is dt 0.
> 
> > Here we hit a snag: what do the numeric dashtypes exactly mean?
> > ...
> > One final question: what about user-specified patterns? Are they needed
> > at all? If yes, what would be the preferred syntax?
> > Should there be a separate "set dashtype" command where the user could
> > set explicit dash and space lengths? This would offer the most
> > flexibility, but it would be hard to implement it across all terminals.
> 
> See above.  I think we are in agreement.
> 
> > Or should there be separate keywords, like "solid", "dashed", "dot-dash"
> > etc?
> 
> I don't like that in the general case, but I suppose it might be
> useful to accept "solid" as a synonym for "dt 1"  ...

Do you mean synonym for "dt 0"?

Keywords like "dashed" and "dot-dash" seem too limiting if we want to
support user-defined dash types. But predefined dash types are much
easier to implement.

For the user-specified "set dashtype", the user-given pattern is
implicitly assumed to loop around itself?
  set dashtype 1 "--- "
would end up drawing "--- --- --- --- " etc.?

I assume that each character space in the dashtype string maps to a
minimal-length chunk of line? So '-' is a bit of solid line, and ' ' is
presumably nothing drawn, and '=' would be a double-line. I'm not sure
what '.' is expected to produce? A dot, but raised to centerline, like
'·'?

I thought about inserting other glyphs, e.g. '»'. Or normal letters,
e.g.
  set dashtype 2 "----- A --"
  set dashtype 3 "--- B ----"
But then one has to deal with fonts, sizes, weights, rotation, offset,
etc. Maybe it is better to accomplish that sort of idea with just "set
dashtype 2 "-----   --" and then follow with a second line "with labels"
to fill in the glyphs. But now the user has to try and synchronize the
"set samples" and/or "every" so that the letters all fall into the gaps
in the dashes.

What do linewidth and pointsize mean to a dotted/dashed line? Does a
line with dashtype '···········' ignore pointsize and increasing
linewidth just adds to the vertical height of each dot (thus in the
extreme making it look more like '|||||||||||')? Or will linewidth
implicitly also increase the horizontal spacing so '·' -> '•' -> '●' ...
etc. continues to retain its aspect ratio as it grows larger?