[AGG] Drawing dashed double-lines

[Phil E. <spa...@ch...>]

Dear Experts,

I am attempting to draw a simple dashed double line, i.e. something like

     - - - - - - - - - - - - -
     - - - - - - - - - - - - -

My first attempt used stroke -> dash -> stroke.  This has two problems: 
the lines wrap around the ends, and the dashes on the sides are not 
aligned especially if the line is not straight:

      - - - - - - - - - - - - - - - - -|
     | - - - - - - - - - - - - - - - - -

Then I tried dash -> stroke -> stroke.  This makes the two sides 
aligned, but of course it adds ends to each segment:

     +--+ +--+ +--+ +--+ +--+
     |  | |  | |  | |  | |  |
     +--+ +--+ +--+ +--+ +--+

My final attempt was using contour to make a "left path" and a "right 
path", and to dash and stroke them separately:

contour(width=+n) -> dash -> stroke
contour(width=-n) -> dash -> stroke

This doesn't work either, and I think I am probably misunderstanding 
what contour should do to a non-closed path.

Alignment of the dashes on each side would be good but is not 
essential.  What is essential is not having stuff that wraps around the ends.

I think the easiest way to make this work would be if stroke had a way 
to specify "none" as the cap style.  Then I could do dash -> 
stroke(cap=none) -> stroke.  Is there some way to achieve that?  Or can 
someone suggest another way to do this?


Thanks,  Phil.