3 files changed, 58 insertions, 0 deletions
diff --git a/lib/utils/clamp_path.py b/lib/utils/clamp_path.py
index 0f58f83c..fcb34a4b 100644
--- a/lib/utils/clamp_path.py
+++ b/lib/utils/clamp_path.py
@@ -1,5 +1,6 @@
 from shapely.geometry import LineString, MultiPolygon
 from shapely.geometry import Point as ShapelyPoint
+from shapely.ops import nearest_points
 from shapely.prepared import prep
 
 from .geometry import (Point, ensure_geometry_collection,
@@ -14,6 +15,9 @@ def path_to_segments(path):
 
 def segments_to_path(segments):
     """Convert a list of contiguous LineStrings into a list of Points."""
+    if not segments:
+        return []
+
     coords = [segments[0].coords[0]]
 
     for segment in segments:
@@ -68,6 +72,22 @@ def find_border(polygon, point):
         return polygon.exterior
 
 
+def clamp_fully_external_path(path, polygon):
+    """Clamp a path that lies entirely outside a polygon."""
+
+    start = ShapelyPoint(path[0])
+    end = ShapelyPoint(path[-1])
+
+    start_on_outline = nearest_points(start, polygon.exterior)[1].buffer(0.01, resolution=1)
+    end_on_outline = nearest_points(end, polygon.exterior)[1].buffer(0.01, resolution=1)
+
+    border_pieces = ensure_multi_line_string(polygon.exterior.difference(MultiPolygon((start_on_outline, end_on_outline)))).geoms
+    border_pieces = fix_starting_point(border_pieces)
+    shorter = min(border_pieces, key=lambda piece: piece.length)
+
+    return adjust_line_end(shorter, start)
+
+
 def clamp_path_to_polygon(path, polygon):
     """Constrain a path to a Polygon.
 
@@ -143,4 +163,7 @@ def clamp_path_to_polygon(path, polygon):
         else:
             was_inside = False
 
+    if not result:
+        return clamp_fully_external_path(path, polygon)
+
     return segments_to_path(result)
diff --git a/lib/utils/geometry.py b/lib/utils/geometry.py
index 24cf8459..541d9cbc 100644
--- a/lib/utils/geometry.py
+++ b/lib/utils/geometry.py
@@ -197,6 +197,37 @@ def cut_path(points, length):
     return [Point(*point) for point in subpath.coords]
 
 
+def offset_points(pos1, pos2, offset_px, offset_proportional):
+    """Expand or contract two points about their midpoint.
+
+    This is useful for pull compensation and insetting underlay.
+    """
+
+    distance = (pos1 - pos2).length()
+
+    if distance < 0.0001:
+        # if they're the same point, we don't know which direction
+        # to offset in, so we have to just return the points
+        return pos1, pos2
+
+    # calculate the offset for each side
+    offset_a = offset_px[0] + (distance * offset_proportional[0])
+    offset_b = offset_px[1] + (distance * offset_proportional[1])
+    offset_total = offset_a + offset_b
+
+    # don't contract beyond the midpoint, or we'll start expanding
+    if offset_total < -distance:
+        scale = -distance / offset_total
+        offset_a = offset_a * scale
+        offset_b = offset_b * scale
+
+    # convert offset to float before using because it may be a numpy.float64
+    out1 = pos1 + (pos1 - pos2).unit() * float(offset_a)
+    out2 = pos2 + (pos2 - pos1).unit() * float(offset_b)
+
+    return out1, out2
+
+
 class Point:
     def __init__(self, x: typing.Union[float, numpy.float64], y: typing.Union[float, numpy.float64]):
         self.x = float(x)
diff --git a/lib/utils/list.py b/lib/utils/list.py
index efa3969e..e5838b5a 100644
--- a/lib/utils/list.py
+++ b/lib/utils/list.py
@@ -21,3 +21,7 @@ def poprandom(sequence, rng=_rng):
         sequence[index] = last_item
 
     return item
+
+
+def is_all_zeroes(sequence):
+    return all(item == 0 for item in sequence)