Hi Will,
On Fri, Dec 03, 2010 at 11:49:20AM -0600, William Henney wrote:
> 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).
Well, the cleanest way I see would be to clone the
graph.style.arrow-class and create a new plot-style which does not plot
an arrow (I call it "arrow_line"). By deriving it from the class
"graph.style.arrow", it behaces exactly as that class. So I only
overwrite one function: the one, which draws the lines+arrows. This
function is a copy from the original function where I just removed the
arrow ;-)
from pyx import *
import math
# derive the class from graph.style.arrow
class arrow_line(graph.style.arrow):
# overload only the plot-function
def drawpoint(self, privatedata, sharedata, graph, point):
if privatedata.lineattrs is not None and privatedata.arrowattrs is not
None and sharedata.vposvalid:
linelength_pt = unit.topt(self.linelength)
x_pt, y_pt = graph.vpos_pt(*sharedata.vpos)
try:
angle = point["angle"] + 0.0
size = point["size"] + 0.0
except:
pass
else:
if point["size"] > self.epsilon:
dx = math.cos(angle*math.pi/180)
dy = math.sin(angle*math.pi/180)
x1 = x_pt-self.arrowpos*dx*linelength_pt*size
y1 = y_pt-self.arrowpos*dy*linelength_pt*size
x2 = x_pt+(1-self.arrowpos)*dx*linelength_pt*size
y2 = y_pt+(1-self.arrowpos)*dy*linelength_pt*size
privatedata.arrowcanvas.stroke(path.line_pt(x1, y1,x2, y2),
privatedata.lineattrs)
# test & use ist:
# just some data to plot
d = [ [i,j,(i+j)/10.,2*math.pi/10.*i] for i in range(10) for j in range(10)]
# the graph...
g = graph.graphxy(width=10)
g.plot(graph.data.points(d,x=1,y=2,size=3,angle=4),[arrow_line()])
g.writePDFfile("p")
(Of course this code is not 100% clean: You can pass the argument
"arrowsize" to my new class "arrow_line", which is quite stupid... From
that point of view, it would be cleaner to rewrite the complete class.
And the most powerfull solution would be a new arrow-class in pyx, where
the arrow can be passed as parameter ;-))
Axel
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