matplotlib · dstansby · Jan 1, 2023 · Dec 29, 2022
diff --git a/examples/event_handling/poly_editor.py b/examples/event_handling/poly_editor.py
@@ -14,37 +14,24 @@
     You can copy and paste individual parts, or download the entire example
     using the link at the bottom of the page.
 """
+
 import numpy as np
 from matplotlib.lines import Line2D
 from matplotlib.artist import Artist
 
 
-def dist(x, y):
-    """
-    Return the distance between two points.
-    """
-    d = x - y
-    return np.sqrt(np.dot(d, d))
-
-
 def dist_point_to_segment(p, s0, s1):
     """
-    Get the distance of a point to a segment.
-      *p*, *s0*, *s1* are *xy* sequences
-    This algorithm from
-    http://www.geomalgorithms.com/algorithms.html
+    Get the distance from the point *p* to the segment (*s0*, *s1*), where
+    *p*, *s0*, *s1* are ``[x, y]`` arrays.
     """
-    v = s1 - s0
-    w = p - s0
-    c1 = np.dot(w, v)
-    if c1 <= 0:
-        return dist(p, s0)
-    c2 = np.dot(v, v)
-    if c2 <= c1:
-        return dist(p, s1)
-    b = c1 / c2
-    pb = s0 + b * v
-    return dist(p, pb)
+    s01 = s1 - s0
+    s0p = p - s0
+    if (s01 == 0).all():
+        return np.hypot(*s0p)
+    # Project onto segment, without going past segment ends.
+    p1 = s0 + np.clip((s0p @ s01) / (s01 @ s01), 0, 1) * s01
+    return np.hypot(*(p - p1))
 
 
 class PolygonInteractor:

diff --git a/lib/mpl_toolkits/mplot3d/axes3d.py b/lib/mpl_toolkits/mplot3d/axes3d.py
@@ -1066,7 +1066,7 @@ def format_coord(self, xd, yd):
         # nearest edge
         p0, p1 = min(self._tunit_edges(),
                      key=lambda edge: proj3d._line2d_seg_dist(
-                         edge[0], edge[1], (xd, yd)))
+                         (xd, yd), edge[0][:2], edge[1][:2]))
 
         # scale the z value to match
         x0, y0, z0 = p0

diff --git a/lib/mpl_toolkits/mplot3d/proj3d.py b/lib/mpl_toolkits/mplot3d/proj3d.py
@@ -6,31 +6,27 @@
 import numpy.linalg as linalg
 
 
-def _line2d_seg_dist(p1, p2, p0):
+def _line2d_seg_dist(p, s0, s1):
     """
-    Return the distance(s) from line defined by p1 - p2 to point(s) p0.
+    Return the distance(s) from point(s) *p* to segment(s) (*s0*, *s1*).
 
-    p0[0] = x(s)
-    p0[1] = y(s)
-
-    intersection point p = p1 + u*(p2-p1)
-    and intersection point lies within segment if u is between 0 and 1.
-
-    If p1 and p2 are identical, the distance between them and p0 is returned.
-    """
-
-    x01 = np.asarray(p0[0]) - p1[0]
-    y01 = np.asarray(p0[1]) - p1[1]
-    if np.all(p1[0:2] == p2[0:2]):
-        return np.hypot(x01, y01)
-
-    x21 = p2[0] - p1[0]
-    y21 = p2[1] - p1[1]
-    u = (x01*x21 + y01*y21) / (x21**2 + y21**2)
-    u = np.clip(u, 0, 1)
-    d = np.hypot(x01 - u*x21, y01 - u*y21)
-
-    return d
+    Parameters
+    ----------
+    p : (ndim,) or (N, ndim) array-like
+        The points from which the distances are computed.
+    s0, s1 : (ndim,) or (N, ndim) array-like
+        The xy(z...) coordinates of the segment endpoints.
+    """
+    s0 = np.asarray(s0)
+    s01 = s1 - s0  # shape (ndim,) or (N, ndim)
+    s0p = p - s0  # shape (ndim,) or (N, ndim)
+    l2 = s01 @ s01  # squared segment length
+    # Avoid div. by zero for degenerate segments (for them, s01 = (0, 0, ...)
+    # so the value of l2 doesn't matter; this just replaces 0/0 by 0/1).
+    l2 = np.where(l2, l2, 1)
+    # Project onto segment, without going past segment ends.
+    p1 = s0 + np.multiply.outer(np.clip(s0p @ s01 / l2, 0, 1), s01)
+    return ((p - p1) ** 2).sum(axis=-1) ** (1/2)
 
 
 def world_transformation(xmin, xmax,

diff --git a/lib/mpl_toolkits/mplot3d/tests/test_axes3d.py b/lib/mpl_toolkits/mplot3d/tests/test_axes3d.py
@@ -1120,8 +1120,8 @@ def test_lines_dists():
     ys = (100, 150, 30, 200)
     ax.scatter(xs, ys)
 
-    dist0 = proj3d._line2d_seg_dist(p0, p1, (xs[0], ys[0]))
-    dist = proj3d._line2d_seg_dist(p0, p1, np.array((xs, ys)))
+    dist0 = proj3d._line2d_seg_dist((xs[0], ys[0]), p0, p1)
+    dist = proj3d._line2d_seg_dist(np.array((xs, ys)).T, p0, p1)
     assert dist0 == dist[0]
 
     for x, y, d in zip(xs, ys, dist):
@@ -1133,15 +1133,11 @@ def test_lines_dists():
 
 
 def test_lines_dists_nowarning():
-    # Smoke test to see that no RuntimeWarning is emitted when two first
-    # arguments are the same, see GH#22624
-    p0 = (10, 30, 50)
-    p1 = (10, 30, 20)
-    p2 = (20, 150)
-    proj3d._line2d_seg_dist(p0, p0, p2)
-    proj3d._line2d_seg_dist(p0, p1, p2)
-    p0 = np.array(p0)
-    proj3d._line2d_seg_dist(p0, p0, p2)
+    # No RuntimeWarning must be emitted for degenerate segments, see GH#22624.
+    s0 = (10, 30, 50)
+    p = (20, 150, 180)
+    proj3d._line2d_seg_dist(p, s0, s0)
+    proj3d._line2d_seg_dist(np.array(p), s0, s0)
 
 
 def test_autoscale():