Hi, transparency is certainly not a good idea, as the length of the line is shortened by the arrow. (The arrow is an ornament at the decorated path, and excludes parts of the original path from drawing.) Furthermore you will keep all the arrow paths in the output; they will just be invisible.
While clearing attributes does look interesting, a deco.arrow.clear in the
lineattrs does not prevent the arrow from being drawn as the arrow decorator is
added after the lineattrs. On the other hand it is correct that the line attrs
are added first, as by that you can for example set the color of the line and
the arrow by setting a color for the lineattrs. Unfortunately there is a strict
rule when merging attrs, that an attr can influence preceeding attrs only, but
not attrs added afterwards. To my mind we should not question this behavior.
The solution Axel proposed in this thread is the way to go. However, you may
just copy the whole arrow style and remove all arrow stuff from it keeping the
lines only.
While I think we should not allow for size=None in the arrow decorator, I don't
see any particular problem to allow arrowsize=0 in the graph.arrow style for a
very simple solution to your problem. I submitted a patch in changeset 3034, so
in case you use the SVN version of PyX, just update, set arrowsize to None and
you're done.
Best,
André
Am 03.12.2010 um 18:49 schrieb William Henney:
> Hi list
>
> I am trying to produce a vector plot with pyx.graph.style.arrow() in
> which the arrow heads do not appear.
>
> The only working solution I have found is to put
>
> pyx.graph.style.arrow(arrowattrs=[pyx.color.transparency(1.0)])
>
> but this does not seem like a "clean" solution.
>
> The following two attempted solutions did not work:
>
> 1. pyx.graph.style.arrow(arrowattrs=[attr.clear])
>
> File
> "/Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/pyx/deco.py",
> line 240, in processPDF
> raise RuntimeError("Path neither to be stroked nor filled nor
> decorated in another way")
>
> 2. pyx.graph.style.arrow(arrowsize=0)
>
> File
> "/Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/pyx/normpath.py",
> line 957, in close
> raise NormpathException("Normsubpath too short, cannot be closed")
>
> Is there a better way than transparency to achieve this? The reason I
> don't want arrow heads is that the field I am plotting is of
> polarization "vectors", for which there is no distinction between the
> angle theta and the angle (theta + 180 deg).
>
> Cheers
>
> Will
>
> --
>
> Dr William Henney, Centro de Radioastronomía y Astrofísica,
> Universidad Nacional Autónoma de México, Campus Morelia
>
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