From db33246d6ee680da326d1a2d71d396730fd49d0d Mon Sep 17 00:00:00 2001
From: Andy <andyaport@gmail.com>
Date: Thu, 6 Apr 2017 21:57:20 -0700
Subject: [PATCH] add direction_field.py

---
 svgpathtools/directional_field.py | 79 +++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 svgpathtools/directional_field.py

diff --git a/svgpathtools/directional_field.py b/svgpathtools/directional_field.py
new file mode 100644
index 0000000..fa39abb
--- /dev/null
+++ b/svgpathtools/directional_field.py
@@ -0,0 +1,79 @@
+# External dependencies
+from __future__ import division, absolute_import, print_function
+import numpy as np
+
+# Internal dependencies
+from svgpathtools import *
+
+
+def directional_field(curve, tvals=3, asize=1e-2,
+                      colored=False):
+    """Creates/Displays a directional_field for the given curve.
+
+    Parameters
+    ----------
+
+    curve: `Path` or any path segment object
+        the curve to find the directional field for.
+
+    tvals: iterable or `int`
+        if  tvals is a `int`, then will determine the number of arrows per
+        segment.  Otherwise, an arrow will be placed at `curve.point(t)` for
+        each `t` in `tvals`.
+
+    asize: float-like or int-like
+        relative size of the arrowheads (relative to `curve.length()`).
+
+    colored: `bool`
+        if true (defaults `False`), will return a 3-tuple of (arrowhead paths,
+        tvals, colors).
+
+    Returns
+    -------
+
+    A path composed of arrowheads, unless `colored` is true, see above for that
+    case.
+
+    Example Usages
+    -------------_
+
+    >>> p = Path(Line(0,1), Line(1,1+1j), Line(1+1j,1j), Line(1j,1))
+    >>> disvg([p, directional_field(p)])
+
+    >>> p = Path(Line(0,1), Line(1,1+1j), Line(1+1j,1j), Line(1j,1))
+    >>> arrows, tvals, colors  = directional_field(p, colored=True)
+    >>> disvg([p]+arrows, ['green']+colors)
+
+    """
+
+    if isinstance(tvals, int):
+        if isinstance(curve, Path):
+            tvals = [curve.t2T(k, t) for k in range(tvals)
+                                      for t in np.linspace(0, 1, tvals)]
+        else:
+            tvals = np.linspace(0, 1, tvals)
+
+    size = asize * curve.length()
+
+    arrows = []
+    for t in tvals:
+        pt = curve.point(t)
+        ut = curve.unit_tangent(t)
+        un = curve.normal(t)
+        l1 = Line(pt, pt + size*(un - ut)/2).reversed()
+        l2 = Line(pt, pt + size*(-un - ut)/2)
+        if colored:
+            arrows.append(Path(l1, l2))
+        else:
+            arrows += [l1, l2]
+
+    if colored:
+        colors = [(int(255*t), 0, 0) for t in tvals]
+        return arrows, tvals, colors
+    else:
+        return Path(*arrows)
+
+
+
+p = Path(Line(0,1), Line(1,1+1j), Line(1+1j,1j), Line(1j,0))
+disvg([p, directional_field(p)])