1 files changed, 119 insertions, 0 deletions
diff --git a/lib/extensions/convert_to_satin.py b/lib/extensions/convert_to_satin.py
new file mode 100644
index 00000000..715853c4
--- /dev/null
+++ b/lib/extensions/convert_to_satin.py
@@ -0,0 +1,119 @@
+import inkex
+from shapely import geometry as shgeo
+from itertools import chain
+
+from .base import InkstitchExtension
+from ..svg.tags import SVG_PATH_TAG
+from ..svg import get_correction_transform, PIXELS_PER_MM
+from ..elements import Stroke
+from ..utils import Point
+
+
+class ConvertToSatin(InkstitchExtension):
+    """Convert a line to a satin column of the same width."""
+
+    def effect(self):
+        if not self.get_elements():
+            return
+
+        if not self.selected:
+            inkex.errormsg(_("Please select at least one line to convert to a satin column."))
+            return
+
+        if not all(isinstance(item, Stroke) for item in self.elements):
+            # L10N: Convert To Satin extension, user selected one or more objects that were not lines.
+            inkex.errormsg(_("Only simple lines may be converted to satin columns."))
+            return
+
+        for element in self.elements:
+            parent = element.node.getparent()
+            index = parent.index(element.node)
+            correction_transform = get_correction_transform(element.node)
+
+            for path in element.paths:
+                try:
+                    rails, rungs = self.path_to_satin(path, element.stroke_width)
+                except ValueError:
+                    inkex.errormsg(_("Cannot convert %s to a satin column because it intersects itself.  Try breaking it up into multiple paths.") % element.node.get('id'))
+
+                parent.insert(index, self.satin_to_svg_node(rails, rungs, correction_transform))
+
+            parent.remove(element.node)
+
+    def path_to_satin(self, path, stroke_width):
+        path = shgeo.LineString(path)
+
+        left_rail = path.parallel_offset(stroke_width / 2.0, 'left')
+        right_rail = path.parallel_offset(stroke_width / 2.0, 'right')
+
+        if not isinstance(left_rail, shgeo.LineString) or \
+           not isinstance(right_rail, shgeo.LineString):
+                # If the parallel offsets come out as anything but a LineString, that means the
+                # path intersects itself, when taking its stroke width into consideration.  See
+                # the last example for parallel_offset() in the Shapely documentation:
+                #   https://shapely.readthedocs.io/en/latest/manual.html#object.parallel_offset
+                raise ValueError()
+
+        # for whatever reason, shapely returns a right-side offset's coordinates in reverse
+        left_rail = list(left_rail.coords)
+        right_rail = list(reversed(right_rail.coords))
+
+        rungs = self.generate_rungs(path, stroke_width)
+
+        return (left_rail, right_rail), rungs
+
+    def generate_rungs(self, path, stroke_width):
+        rungs = []
+
+        # approximately 1cm between rungs, and we don't want them at the very start or end
+        num_rungs = int(path.length / PIXELS_PER_MM / 10) - 1
+
+        if num_rungs < 1 or num_rungs == 2:
+            # avoid 2 rungs because it can be ambiguous (which are the rails and which are the
+            # rungs?)
+            num_rungs += 1
+
+        distance_between_rungs = path.length / (num_rungs + 1)
+
+        for i in xrange(num_rungs):
+            rung_center = path.interpolate((i + 1) * distance_between_rungs)
+            rung_center = Point(rung_center.x, rung_center.y)
+
+            # TODO: use bezierslopeatt or whatever
+            # we need to calculate the normal at this point so grab another point just a little
+            # further down the path, effectively grabbing a small segment of the path
+            segment_end = path.interpolate((i + 1) * distance_between_rungs + 0.1)
+            segment_end = Point(segment_end.x, segment_end.y)
+
+            tangent = segment_end - rung_center
+            normal = tangent.unit().rotate_left()
+            offset = normal * stroke_width * 0.75
+
+            rung_start = rung_center + offset
+            rung_end = rung_center - offset
+
+            rungs.append((rung_start.as_tuple(), rung_end.as_tuple()))
+
+        return rungs
+        import sys
+        print >> sys.stderr, rails, rungs
+
+
+
+    def satin_to_svg_node(self, rails, rungs, correction_transform):
+        d = ""
+        for path in chain(rails, rungs):
+            d += "M"
+            for x, y in path:
+                d += "%s,%s " % (x, y)
+            d += " "
+
+        return inkex.etree.Element(SVG_PATH_TAG,
+            {
+                "id": self.uniqueId("path"),
+                "style": "stroke:#000000;stroke-width:1px;fill:none",
+                "transform": correction_transform,
+                "d": d,
+                "embroider_satin_column": "true",
+            }
+        )