tidy path_to_curves

lib/stitches/running_stitch.py

@@ -183,7 +183,7 @@ def take_stitch(start: Point, points: typing.Sequence[Point], idx: int, stitch_l
     return points[-1], None
 
 
-def stitch_curve_even(points: typing.Sequence[Point], stitch_length: float, tolerance: float):
+def stitch_curve_evenly(points: typing.Sequence[Point], stitch_length: float, tolerance: float):
     # Will split a straight line into even-length stitches while still handling curves correctly.
     # Includes end point but not start point.
     if len(points) < 2:
@@ -216,23 +216,29 @@ def path_to_curves(points: typing.List[Point], min_len: float):
     if len(points) < 3:
         return [points]
     curves = []
+
     last = 0
     last_seg = points[1] - points[0]
     seg_len = last_seg.length()
     for i in range(1, len(points) - 1):
+        # vectors of the last and next segments
         a = last_seg
         b = points[i + 1] - points[i]
         aabb = (a * a) * (b * b)
         abab = (a * b) * abs(a * b)
+
+        # Test if the turn angle from vectors a to b is more than 45 degrees
+        # Uses the property of inner products that abab = ± aabb * cos(angle(a,b))**2
         if aabb > 0 and abab < 0.5 * aabb:
-            # inner angle of at most 135 deg
             if seg_len >= min_len:
                 curves.append(points[last: i + 1])
                 last = i
             seg_len = 0
+
         if b * b > 0:
             last_seg = b
         seg_len += b.length()
+
     curves.append(points[last:])
     return curves
 
@@ -242,7 +248,7 @@ def running_stitch(points, stitch_length, tolerance):
     stitches = [points[0]]
     for curve in path_to_curves(points, 2 * tolerance):
         # segments longer than twice the tollerance will usually be forced by it, so set that as the minimum for corner detection
-        stitches.extend(stitch_curve_even(curve, stitch_length, tolerance))
+        stitches.extend(stitch_curve_evenly(curve, stitch_length, tolerance))
     return stitches