Twirler; add extra_zeta

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/moebius.py b/moebius.py
index 944ea9b32f63695d1c2a803071a6bed9992b6a2b..3b7ad4684379c25c31f0e55d9e443323c9e48468 100644 (file)
--- a/moebius.py
+++ b/moebius.py
@@ -42,8 +42,8 @@ class Twirler(ParametricCircle):
     tw._cycles = cycles
     tw._begin_zeta = begin_zeta
     tw._axis = np.cross(r0, r1)
-  def dirn(tw, theta):
-    zeta = tw._begin_zeta + theta * tw._cycles
+  def dirn(tw, theta, extra_zeta=0):
+    zeta = tw._begin_zeta + theta * tw._cycles + extra_zeta
     r = tw.radius(theta)
     return cos(zeta) * r + sin(zeta) * tw._axis