generalize Element.shape and implement in all element types

lib/elements/element.py

@@ -205,6 +205,10 @@ class EmbroideryElement(object):
     def parse_path(self):
         return apply_transforms(self.path, self.node)
 
+    @property
+    def shape(self):
+        raise NotImplementedError("INTERNAL ERROR: %s must implement shape()", self.__class__)
+
     @property
     @cache
     def commands(self):

lib/elements/polyline.py

@@ -1,3 +1,5 @@
+from shapely import geometry as shgeo
+
 from .element import param, EmbroideryElement, Patch
 from ..i18n import _
 from ..utils.geometry import Point
@@ -27,6 +29,11 @@ class Polyline(EmbroideryElement):
 
        return points
 
+    @property
+    @cache
+    def shape(self):
+        return shgeo.LineString(self.points)
+
     @property
     def path(self):
         # A polyline is a series of connected line segments described by their

lib/elements/satin_column.py

@@ -87,6 +87,17 @@ class SatinColumn(EmbroideryElement):
         # the edges of the satin column.
         return self.get_float_param("zigzag_underlay_inset_mm") or self.contour_underlay_inset / 2.0
 
+    @property
+    @cache
+    def shape(self):
+        # This isn't used for satins at all, but other parts of the code
+        # may need to know the general shape of a satin column.
+
+        flattened = self.flatten(self.parse_path())
+        line_strings = [shgeo.LineString(path) for path in flattened]
+
+        return shgeo.MultiLineString(line_strings)
+
     @property
     @cache
     def csp(self):

lib/elements/stroke.py

@@ -1,4 +1,5 @@
 import sys
+import shapely.geometry
 
 from .element import param, EmbroideryElement, Patch
 from ..i18n import _
@@ -50,6 +51,12 @@ class Stroke(EmbroideryElement):
         else:
             return self.flatten(path)
 
+    @property
+    @cache
+    def shape(self):
+        line_strings = [shapely.geometry.LineString(path) for path in self.paths]
+        return shapely.geometry.MultiLineString(line_strings)
+
     @property
     @param('manual_stitch', _('Manual stitch placement'), tooltip=_("Stitch every node in the path.  Stitch length and zig-zag spacing are ignored."), type='boolean', default=False)
     def manual_stitch_mode(self):