1 files changed, 66 insertions, 0 deletions
diff --git a/lib/stitches/running_stitch.py b/lib/stitches/running_stitch.py
new file mode 100644
index 00000000..81124339
--- /dev/null
+++ b/lib/stitches/running_stitch.py
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+""" Utility functions to produce running stitches. """
+
+
+def running_stitch(points, stitch_length):
+    """Generate running stitch along a path.
+
+    Given a path and a stitch length, walk along the path in increments of the
+    stitch length.  If sharp corners are encountered, an extra stitch will be
+    added at the corner to avoid rounding the corner.  The starting and ending
+    point are always stitched.
+
+    The path is described by a set of line segments, each connected to the next.
+    The line segments are described by a sequence of points.
+    """
+
+    if len(points) < 2:
+        return []
+
+    output = [points[0]]
+    segment_start = points[0]
+    last_segment_direction = None
+
+    # This tracks the distance we've travelled along the current segment so
+    # far.  Each time we make a stitch, we add the stitch_length to this
+    # value.  If we fall off the end of the current segment, we carry over
+    # the remainder to the next segment.
+    distance = 0.0
+
+    for segment_end in points[1:]:
+        segment = segment_end - segment_start
+        segment_length = segment.length()
+
+        if segment_length == 0:
+            continue
+
+        segment_direction = segment.unit()
+
+        # corner detection
+        if last_segment_direction:
+            cos_angle_between = segment_direction * last_segment_direction
+
+            # This checks whether the corner is sharper than 45 degrees.
+            if cos_angle_between < 0.5:
+                # Only add the corner point if it's more than 0.1mm away to
+                # avoid a double-stitch.
+                if (segment_start - output[-1]).length() > 0.1:
+                    # add a stitch at the corner
+                    output.append(segment_start)
+
+                    # next stitch needs to be stitch_length along this segment
+                    distance = stitch_length
+
+        while distance < segment_length:
+            output.append(segment_start + distance * segment_direction)
+            distance += stitch_length
+
+        # prepare for the next segment
+        segment_start = segment_end
+        last_segment_direction = segment_direction
+        distance -= segment_length
+
+    # stitch the last point unless we're already almos there
+    if (segment_start - points[-1]).length() > 0.1:
+        output.append(segment_start)
+
+    return output