From 69bf8eafc6d36977504a21dc97bcc4b455ff037e Mon Sep 17 00:00:00 2001
From: Michael Schindler <m-schindler@users.sourceforge.net>
Date: Thu, 4 Aug 2005 11:35:07 +0000
Subject: [PATCH] Add the knot example for showing the parallel deformer

git-svn-id: https://pyx.svn.sourceforge.net/svnroot/pyx/trunk/pyx@2327 069f4177-920e-0410-937b-c2a4a81bcd90
---
 examples/path/INDEX   |  1 +
 examples/path/knot.py | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 examples/path/knot.py

diff --git a/examples/path/INDEX b/examples/path/INDEX
index 9ad535a5..b159f1cf 100644
--- a/examples/path/INDEX
+++ b/examples/path/INDEX
@@ -2,3 +2,4 @@ circles
 sierpinski
 tree
 springs
+knot
diff --git a/examples/path/knot.py b/examples/path/knot.py
new file mode 100644
index 00000000..42a0b704
--- /dev/null
+++ b/examples/path/knot.py
@@ -0,0 +1,67 @@
+from pyx import *
+unit.set(uscale=3, wscale=3)
+
+dist = 0.15           # distance between the ropes
+thick = 0.08          # distance between the ropes
+
+# build the basepath of the knot. This is the curve that lies
+# between both ropes.
+A = 1.0, 0.1    # point where the knot starts after the straight line
+B = 1.3, 0      # point where the knot is curved, overlying the straight line
+t = -0.8, -0.1  # direction at A
+s =  0.3, 1.2   # direction at B
+pts = [
+  ( A[0]-t[0], A[1]-t[1]), ( A[0]     , A[1]     ),
+  ( A[0]+t[0], A[1]+t[1]), (-B[0]-s[0],-B[1]-s[1]),
+  (-B[0]     ,-B[1]     ), (-B[0]+s[0],-B[1]+s[1]),
+  ( B[0]-s[0], B[1]-s[1]), ( B[0]     , B[1]     ),
+  ( B[0]+s[0], B[1]+s[1]), (-A[0]-t[0],-A[1]-t[1]),
+  (-A[0]     ,-A[1]     ), (-A[0]+t[0],-A[1]+t[1]) ]
+seam = path.path(
+  path.moveto(*(pts[0])),
+  path.lineto(*(pts[1])),
+  path.curveto(pts[2][0],pts[2][1],pts[3][0],pts[3][1],pts[4][0],pts[4][1]),
+  path.curveto(pts[5][0],pts[5][1],pts[6][0],pts[6][1],pts[7][0],pts[7][1]),
+  path.curveto(pts[8][0],pts[8][1],pts[9][0],pts[9][1],pts[10][0],pts[10][1]),
+  path.lineto(*(pts[11])) )
+# We smooth this curve a little because we used curveto together with lineto
+seam = deformer.smoothed(0.4).deform(seam)
+
+
+# The ropes, when drawn later, will have to overlap in a very specific way.
+# We need to split them at appropriate points.
+# This gives a list of segments for the middle curve
+l = seam.arclen()
+seam_segs = seam.split([0.28*l,0.42*l, 0.58*l, 0.72*l])
+
+
+# For each segment two shifted paths build the boundaries of each rope
+ropes_segs = []
+for seam_seg in seam_segs:
+    ropes_segs.append([])
+    for ropeshift in [-0.5*dist, 0.5*dist]:
+        ropes_segs[-1].append([])
+        for edgeshift in [-0.5*thick, 0.5*thick]:
+            # We use the parallel deformer to create the parallel segments
+            # for each rope from the base curve:
+            ropes_segs[-1][-1].append(
+              deformer.parallel(ropeshift + edgeshift).deform(seam_seg))
+# Now, ropes_segs is a list of segments, containing a list of ropes,
+# each containing the two bounding paths of the rope segment
+
+
+rope_colors = [color.rgb.blue, color.rgb.red]
+
+c = canvas.canvas()
+# Because the segments should overlap in a very specific manner
+# we have to draw them in the correct order
+for index in [1, 4, 2, 0, 3]:
+    for rope_seg, col in zip(ropes_segs[index], rope_colors):
+        seg = rope_seg[0].joined(rope_seg[1].reversed())
+        seg.append(path.closepath())
+        c.fill(seg, [col])
+        c.stroke(rope_seg[0], [style.linecap.round, style.linejoin.round])
+        c.stroke(rope_seg[1], [style.linecap.round, style.linejoin.round])
+
+c.writeEPSfile("knot")
+c.writePDFfile("knot")
-- 
2.11.4.GIT