From 612f18dc711c6a0fbf554465174b449604abb374 Mon Sep 17 00:00:00 2001
From: Kaalleen <36401965+kaalleen@users.noreply.github.com>
Date: Sun, 31 Aug 2025 11:25:46 +0200
Subject: stroke to satin: ensure a good starting point for closed paths
 (#3944)

starting point for the conversion, not necessarily the resulting column
---
 lib/elements/element.py               |  4 +++
 lib/elements/satin_column.py          |  4 ++-
 lib/elements/utils/stroke_to_satin.py | 47 +++++++++++++++++++++++++++++------
 3 files changed, 46 insertions(+), 9 deletions(-)

(limited to 'lib/elements')

diff --git a/lib/elements/element.py b/lib/elements/element.py
index d830012f..fdc0233f 100644
--- a/lib/elements/element.py
+++ b/lib/elements/element.py
@@ -467,6 +467,10 @@ class EmbroideryElement(object):
 
         return inkex.Path(d).to_superpath()
 
+    @property
+    def is_closed_path(self):
+        return isinstance(self.node.get_path()[-1], inkex.paths.ZoneClose)
+
     @cache
     def parse_path(self):
         return apply_transforms(self.path, self.node)
diff --git a/lib/elements/satin_column.py b/lib/elements/satin_column.py
index 4951f8bf..26b4d534 100644
--- a/lib/elements/satin_column.py
+++ b/lib/elements/satin_column.py
@@ -26,7 +26,7 @@ from ..utils import Point, cache, cut, cut_multiple, offset_points, prng
 from ..utils.param import ParamOption
 from ..utils.threading import check_stop_flag
 from .element import PIXELS_PER_MM, EmbroideryElement, param
-from .utils.stroke_to_satin import convert_path_to_satin
+from .utils.stroke_to_satin import convert_path_to_satin, set_first_node
 from .validation import ValidationError, ValidationWarning
 
 
@@ -625,6 +625,8 @@ class SatinColumn(EmbroideryElement):
         paths = [path for path in self.paths if len(path) > 1]
         if len(paths) == 1:
             style_args = get_join_style_args(self)
+            if self.is_closed_path:
+                set_first_node(paths, self.stroke_width)
             new_satin = convert_path_to_satin(paths[0], self.stroke_width, style_args, rungs_at_nodes=True)
             if new_satin:
                 rails, rungs = new_satin
diff --git a/lib/elements/utils/stroke_to_satin.py b/lib/elements/utils/stroke_to_satin.py
index e75ca5d3..0b8ec819 100644
--- a/lib/elements/utils/stroke_to_satin.py
+++ b/lib/elements/utils/stroke_to_satin.py
@@ -3,18 +3,19 @@
 # Copyright (c) 2025 Authors
 # Licensed under the GNU GPL version 3.0 or later.  See the file LICENSE for details.
 
-from numpy import zeros, convolve, int32, diff, setdiff1d, sign
-from math import degrees, acos
-from ...svg import PIXELS_PER_MM
+import sys
+from math import acos, degrees
 
-from ...utils import Point
-from shapely import geometry as shgeo
 from inkex import errormsg
-from ...utils.geometry import remove_duplicate_points
+from numpy import convolve, diff, int32, setdiff1d, sign, zeros
+from shapely import geometry as shgeo
+from shapely.affinity import rotate, scale
 from shapely.ops import substring
-from shapely.affinity import scale
+
 from ...i18n import _
-import sys
+from ...svg import PIXELS_PER_MM
+from ...utils import Point, roll_linear_ring
+from ...utils.geometry import remove_duplicate_points
 
 
 class SelfIntersectionError(Exception):
@@ -305,3 +306,33 @@ def _merge(section, other_section):
     rungs.extend(other_rungs)
 
     return (rails, rungs)
+
+
+def set_first_node(paths, stroke_width):
+    """
+    Rolls the first path in paths to a starting node which has no intersections and is not within a sharp corner
+
+    paths is expected to be a list with only one closed path.
+    """
+    path = paths[0]
+
+    ring = shgeo.LinearRing(path)
+    buffered_ring = ring.buffer(stroke_width / 2).boundary
+
+    for point1, point2 in zip(path[:-1], path[1:]):
+        line = shgeo.LineString([point1, point2])
+        if line.length == 0:
+            continue
+
+        # create a rung at the center of the line
+        # we know that the line (and therefore it's center) is always straight
+        scale_factor = (stroke_width + 0.001) / line.length
+        rung = rotate(line, 90)
+        rung = scale(rung, xfact=scale_factor, yfact=scale_factor)
+
+        # when the rung intersects twice with the buffered ring, we assume a good starting point
+        intersection = rung.intersection(buffered_ring)
+        if isinstance(intersection, shgeo.MultiPoint) and len(intersection.geoms) == 2:
+            distance = ring.project(line.centroid)
+            paths[0] = list(roll_linear_ring(ring, distance).coords)
+            break
-- 
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