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From: "vovka (vzhbanov AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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Date: Mon, 9 Jul 2018 23:49:44 +0300
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] adventures using arrows (for documentation), or
 cross my lines
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References: <20180702125528 DOT D32CF81F76FE AT turkos DOT aspodata DOT se>
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Hi Karl,

On Mon, Jul 02, 2018 at 02:55:28PM +0200, karl AT aspodata DOT se wrote:
>  I'm trying to make arrows to be used when writing about electronic
> design and theory.
> 
> Here is such a symbol:
> 
> $ cat arrow.sym
> v 20150930 2
> H 3 0 0 0 -1 -1 1 -1 -1 -1 -1 -1 4
> M 0,0
> L -15,74
> L  15,74
> z
> $
> 
> and I can use something like [1] to scale it to a suitable size.
> 
> With thoose symbols I can create things like [2] so I can write about
> the relationship between currents and voltages.
> 
> As can seen from [2] the current arrow looks nice, but the voltage
> arrow goes below the horizontal line, it should stop at the line, not
> go beyond it.
> 
> If we look at the arrow sym (Hierarchy->Down symbol) and set the fill
> type to hollow, we see that the lines has a witdh > 0. Line width = 0
> is useful for filled polygons, since then the corners would be at line
> end coordinates and the arrow wouldn't go below the line in [2].
> 
> There are three ways I could solve the "go below" problem.
> 
> a, nudge the arrow upwards
> b, make the "PATH" object have true line width of 0, at least for filled
>    polygons, i.e. patch gschem/lepton-schematic to make that happen.
> c, use same line width as horiz. line, and use round cap style, i.e. 
>    patch gschem/lepton-schematic so that they honor the cap style entry
>    which is currently completely ignored and and an undocumented cap 
>    style is used instead (called "miter" in postscript), see [3].

You can mitigate the issue a bit by using a smaller line
width. The smallest width is 1, since 0 means "default width"
which is really 10. E.g. use the following path definition line:

H 3 1 0 0 -1 -1 1 -1 -1 -1 -1 -1 4

> 
> I'd prefer c to happen, since that would solve other line corner to 
> straight line situations.
> 
> How difficult is that to implement and would such a patch be accepted ?

Dunno. I implemented capstyle support for lines a few years ago
though some things have changed since then. Please look at
edacairo.c. You can see how it is currently done for lines, and
the eda_cairo_path function is the one to play with in this case,
I believe. You'll probably have to read some docs of how things
are done with cairo. Your patch will be accepted if it works
properly. Just open a PR as described at [1] or send it here.

[1] https://github.com/lepton-eda/lepton-eda/blob/master/CONTRIBUTING.md

-- 
  Vladimir