1 files changed, 21 insertions, 0 deletions
diff --git a/third_party/spiro/curves/offset.py b/third_party/spiro/curves/offset.py
new file mode 100644
index 0000000..c528aec
--- /dev/null
+++ b/third_party/spiro/curves/offset.py
@@ -0,0 +1,21 @@
+# offset curve of piecewise cornu curves
+
+from math import *
+
+import pcorn
+from clothoid import mod_2pi
+
+def seg_offset(seg, d):
+    th0 = seg.th(0)
+    th1 = seg.th(seg.arclen)
+    z0 = [seg.z0[0] + d * sin(th0), seg.z0[1] - d * cos(th0)]
+    z1 = [seg.z1[0] + d * sin(th1), seg.z1[1] - d * cos(th1)]
+    chth = atan2(z1[1] - z0[1], z1[0] - z0[0])
+    return [pcorn.Segment(z0, z1, mod_2pi(chth - th0), mod_2pi(th1 - chth))]
+
+
+def offset(curve, d):
+    segs = []
+    for seg in curve.segs:
+        segs.extend(seg_offset(seg, d))
+    return pcorn.Curve(segs)