[PyX-devel] [RFC/PATCH] graph.style.arrow: allow fine-tuning of the arrow head size

[Michael J G. <mic...@us...>]

Currently, the length of the arrow as well as the size of the arrow head
are scaled by the value of the "size" column, which can get out of hand
quickly for vector field plots.

Introduce an argument "arrowscale" (defaulting to 1) that makes the
arrow head scale by a convex combination of "1" and the value of "size":

1 (default): scale by "size" as before
0: fixed size (as if the value of "size" were 1, just for the arrow
head)

Signed-off-by: Michael J Gruber <mic...@us...>
---
I'll try and reply with two PNGs showing the output for arrowscale=0 (default)
and arrowscale=1.

Alternative to the RFC here, one could think about abstracting to graph.style.deco()
with general decoargs and decokwargs arguments (defaulting to [arrowpos=0.5] and such).
That would make it more complicated to specify a decorator which takes into account "size", though.

 pyx/graph/style.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pyx/graph/style.py b/pyx/graph/style.py
index 1d1e283..57cf2de 100644
--- a/pyx/graph/style.py
+++ b/pyx/graph/style.py
@@ -880,12 +880,13 @@ class arrow(_styleneedingpointpos):
     defaultlineattrs = []
     defaultarrowattrs = []
 
-    def __init__(self, linelength=0.25*unit.v_cm, arrowsize=0.15*unit.v_cm, lineattrs=[], arrowattrs=[], arrowpos=0.5, epsilon=1e-5, decorator=deco.earrow):
+    def __init__(self, linelength=0.25*unit.v_cm, arrowsize=0.15*unit.v_cm, lineattrs=[], arrowattrs=[], arrowpos=0.5, arrowscale=1, epsilon=1e-5, decorator=deco.earrow):
         self.linelength = linelength
         self.arrowsize = arrowsize
         self.lineattrs = lineattrs
         self.arrowattrs = arrowattrs
         self.arrowpos = arrowpos
+        self.arrowscale = arrowscale
         self.epsilon = epsilon
         self.decorator = decorator
 
@@ -930,7 +931,7 @@ class arrow(_styleneedingpointpos):
                     y2 = y_pt+(1-self.arrowpos)*dy*linelength_pt*size
                     if self.decorator:
                         privatedata.arrowcanvas.stroke(path.line_pt(x1, y1, x2, y2),
-                                                       privatedata.lineattrs+[self.decorator(privatedata.arrowattrs, size=self.arrowsize*size)])
+                                                       privatedata.lineattrs+[self.decorator(privatedata.arrowattrs, size=self.arrowsize*((1-self.arrowscale) + self.arrowscale*size))])
                     else:
                         privatedata.arrowcanvas.stroke(path.line_pt(x1, y1, x2, y2), privatedata.lineattrs)
 
-- 
2.7.0.341.gc1754cc