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

[sfeam <sf...@us...>]

On Tuesday, 11 March 2014 08:27:29 AM Tait wrote:
> 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"?

Whichever.  Currently "linetype 0" is the dotted one.
It would be kind of weird if the first and possibly only line in a plot
is anything other than solid, but the sequence starts at lt=1.

 
> 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 ----"

This is already possible in version 4.6 using a combination of 
"pointinterval" and "with labels".  This doesn't involve dashtype
that I can see, although one could imagine providing a shortcut 
that accomplishes the same result with a single command rather than
two separate commands. 

> 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.

That is what the existing "pointinterval" property is for.


> 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?

Currently there is a "dashlength" property that is independent of both
"linewidth" and "pointsize".  However right now this is a terminal 
setting rather than a property of the current line or plot.  We might
want to rethink that.

	Ethan