Re: [PATCH] [pic] Add support for arbitrary polygons

[Thomas DUPOND]

Hello Duncan,


Le 2024-09-30 à 09:03, Duncan Losin via a écrit :
> Hi folks,
>
> I have written a patch to add support for drawing arbitrary polygons
> in pic using the existing syntax for multi-segment lines. They can be
> shaded and filled as expected of other closed objects. Examples
> attached in polygon.pdf.

Tried the patch, it's terrific!  I will include it in my tools :) 
Easily beats what I could do with my shallow knowledge of postscript.

> There is also new syntax for referencing the positions of the
> vertices and edge midpoints:
>
> - .v[er[tex]] expr
> - .v[er[tex]] `expr'
> - .p[oint] expr
> - .p[oint] `expr'

Being able to work with points relative to the vertices or midpoints 
with .v `expr' + (1,2) is really a nice touch.  I struggled a bit at 
first because I didn't read the documentation correctly :)

> I must admit I have a very limited computer science education, so I
> expect my implementation could use some improvements; feedback would
> be appreciated. I'm not entirely pleased with how vertex_number is
> set, but I struggled with polygon_object not being instanced until
> the end of object_spec::make_line. That seems to be the general
> structure of the program so I didn't want to change it, but perhaps
> there's a better way to set the value, among other things.

I cannot help here in any way but I had no issues with for me it's good 
enough.

> I've also included the following small documentation update. Where
> referring to ordinals the documentation included the characters " ` "
> and " ' " i.e. the grave accent and apostrophe. These are the correct
> characters, but groff draws these as the left and right quotation
> marks, which confused me when I tried to use this feature. I've
> updated those characters to the appropriate escape sequences "\[ga]"
> and "\[aq]" so that they appear properly.
>
> Future Work: If I understand it correctly (big if), PostScript
> interprets all polygons as a path, much like how pic draws multi-line
> segments. PostScript however can include arcs and splines as segments
> and fill the resulting shape. It doesn't look like it would be
> terribly difficult to implement this in pic, but it would be a lot of
> work. I believe pic, groff, and grops would all need to updated to
> accommodate the new drawing command.

That would be very nice, I wanted to draw the contour of a rail and 
having spline would make this feasible.

Thank you so much for this patch.

--
Best,
Thomas