[PyX-devel] [PATCH] deco.arrow: introduce relarclenpos and friends

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

The pos argument of deco.arrow() maps the range [0,1] to the range of
available positions such that the arrow head can be constructed from the
path without extrapolation. This is useful especially for begin and end
heads, but different from the positioning of other decorators such as
deco.text().

Introduce additional position parameters relarclenpos, arclenfrombegin
and arclendfromend which work exactly like for other decorators. They
all default to None, which means that the pos argument is used and the
behaviour of deco.arrow() is unchanged unless you specify a value for
one of the new arguments.

Also, introduce a new center argument which specifies the center of the
arrow head (multiples of its size). It defaults to the center of mass of
a solid triangular arrow head but is used only when any of the new
position parameters is specified.

Signed-off-by: Michael J Gruber <mic...@us...>
---
 pyx/deco.py | 40 ++++++++++++++++++++++++++++++++++------
 1 file changed, 34 insertions(+), 6 deletions(-)

diff --git a/pyx/deco.py b/pyx/deco.py
index e41e88e..58b9712 100644
--- a/pyx/deco.py
+++ b/pyx/deco.py
@@ -432,14 +432,19 @@ class arrow(deco, attr.attr):
 
     """arrow is a decorator which adds an arrow to either side of the path"""
 
-    def __init__(self, attrs=[], pos=1, reversed=0, size=_base, angle=45, constriction=0.8):
+    def __init__(self, attrs=[], pos=1, relarclenpos=None, arclenfrombegin=None, arclenfromend=None,
+                       reversed=0, size=_base, angle=45, constriction=0.8, center=0.666667):
         self.attrs = attr.mergeattrs([style.linestyle.solid, filled] + attrs)
         attr.checkattrs(self.attrs, [deco, style.fillstyle, style.strokestyle])
         self.pos = pos
+        self.relarclenpos = relarclenpos
+        self.arclenfrombegin = arclenfrombegin
+        self.arclenfromend = arclenfromend
         self.reversed = reversed
         self.size = size
         self.angle = angle
         self.constriction = constriction
+        self.center = center
 
         # calculate absolute arc length of constricition
         # Note that we have to correct this length because the arrowtemplates are rotated
@@ -453,11 +458,18 @@ class arrow(deco, attr.attr):
             # need constrictionlen for cutting the path
             self.constrictionlen = self.size * 1 * math.cos(math.radians(self.angle/2.0))
 
-    def __call__(self, attrs=None, pos=None, reversed=None, size=None, angle=None, constriction=_marker):
+    def __call__(self, attrs=None, pos=None, relarclenpos=None, arclenfrombegin=None, arclenfromend=None,
+                       reversed=None, size=None, angle=None, constriction=_marker, center=None):
         if attrs is None:
             attrs = self.attrs
         if pos is None:
             pos = self.pos
+        if relarclenpos is None:
+            arelrclenpos = self.relarclenpos
+        if arclenfrombegin is None:
+            arclenfrombegin = self.arclenfrombegin
+        if arclenfromend is None:
+            arclenfromend = self.arclenfromend
         if reversed is None:
             reversed = self.reversed
         if size is None:
@@ -466,14 +478,30 @@ class arrow(deco, attr.attr):
             angle = self.angle
         if constriction is _marker:
             constriction = self.constriction
-        return arrow(attrs=attrs, pos=pos, reversed=reversed, size=size, angle=angle, constriction=constriction)
+        if center is None:
+            center = self.center
+        return arrow(attrs=attrs, pos=pos, relarclenpos=relarclenpos, arclenfrombegin=arclenfrombegin,
+                     arclenfromend=arclenfromend, reversed=reversed, size=size, angle=angle, constriction=constriction, center=center)
 
     def decorate(self, dp, texrunner):
         dp.ensurenormpath()
         anormpath = dp.path
 
-        arclenfrombegin = (1-self.reversed)*self.size + self.pos * (anormpath.arclen() - self.size)
+        pos = None
+        if self.arclenfrombegin is not None:
+            arclenfrombegin = self.arclenfrombegin
+        elif self.arclenfromend is not None:
+            arclenfrombegin = anormpath.end() - self.arclenfromend
+        elif self.relarclenpos is not None:
+            # relarcpos is used if neither arcfrombegin nor arcfromend is given
+            arclenfrombegin = self.relarclenpos * anormpath.arclen()
+        else:
+            # pos is used if neither of the above are given
+            pos = self.pos
+            arclenfrombegin = (1-self.reversed)*self.size + pos * (anormpath.arclen() - self.size)
         direction = self.reversed and -1 or 1
+        if pos is None:
+            arclenfrombegin += direction * self.center * self.size
         arrowhead = _arrowhead(anormpath, arclenfrombegin, direction, self.size, self.angle,
                                self.constriction is not None, self.constrictionlen)
 
@@ -481,12 +509,12 @@ class arrow(deco, attr.attr):
         dp.ornaments.draw(arrowhead, self.attrs)
 
         # exlude part of the path from stroking when the arrow is strictly at the begin or the end
-        if self.pos == 0:
+        if pos == 0:
             if self.reversed:
                 dp.excluderange(0, min(self.size, self.constrictionlen))
             else:
                 dp.excluderange(0, min(self.size, self.size - self.constrictionlen))
-        elif self.pos == 1:
+        elif pos == 1:
             if self.reversed:
                 dp.excluderange(anormpath.end() - min(self.size, self.size - self.constrictionlen), anormpath.end())
             else:
-- 
1.7.11.rc0.281.g0a17a8c