user can specify origin for embroidery output by setting up guides (#52)

* user can specify origin using guides

* embroidery origin defaults to center of canvas

embroider.py

@@ -1763,7 +1763,7 @@ class Embroider(inkex.Effect):
 
         patches = elements_to_patches(self.elements)
         stitches = patches_to_stitches(patches, self.options.collapse_length_mm * PIXELS_PER_MM)
-        inkstitch.write_embroidery_file(self.get_output_path(), stitches)
+        inkstitch.write_embroidery_file(self.get_output_path(), stitches, self.document.getroot())
 
         new_layer = inkex.etree.SubElement(self.document.getroot(), SVG_GROUP_TAG, {})
         new_layer.set('id', self.uniqueId("embroidery"))

inkstitch.py

@@ -14,6 +14,7 @@ import simpletransform
 from bezmisc import bezierlength, beziertatlength, bezierpointatt
 from cspsubdiv import cspsubdiv
 import cubicsuperpath
+from shapely import geometry as shgeo
 
 
 try:
@@ -126,12 +127,17 @@ def convert_length(length):
     raise ValueError(_("Unknown unit: %s") % units)
 
 
+@cache
+def get_doc_size(svg):
+    doc_width = convert_length(svg.get('width'))
+    doc_height = convert_length(svg.get('height'))
+
+    return doc_width, doc_height
+
 @cache
 def get_viewbox_transform(node):
     # somewhat cribbed from inkscape-silhouette
-
-    doc_width = convert_length(node.get('width'))
-    doc_height = convert_length(node.get('height'))
+    doc_width, doc_height = get_doc_size(node)
 
     viewbox = node.get('viewBox').strip().replace(',', ' ').split()
 
@@ -504,12 +510,70 @@ def get_flags(stitch):
 
     return flags
 
-def write_embroidery_file(file_path, stitches):
-    # Embroidery machines don't care about our canvas size, so we relocate the
-    # design to the origin.  It might make sense to center it about the origin
-    # instead.
-    min_x = min(stitch.x for stitch in stitches)
-    min_y = min(stitch.y for stitch in stitches)
+
+def _string_to_floats(string):
+    floats = string.split(',')
+    return [float(num) for num in floats]
+
+
+def get_origin(svg):
+    # The user can specify the embroidery origin by defining two guides
+    # named "embroidery origin" that intersect.
+
+    namedview = svg.find(inkex.addNS('namedview', 'sodipodi'))
+    all_guides = namedview.findall(inkex.addNS('guide', 'sodipodi'))
+    label_attribute = inkex.addNS('label', 'inkscape')
+    guides = [guide for guide in all_guides
+                    if guide.get(label_attribute, "").startswith("embroidery origin")]
+
+    # document size used below
+    doc_size = list(get_doc_size(svg))
+
+    # convert the size from viewbox-relative to real-world pixels
+    viewbox_transform = get_viewbox_transform(svg)
+    simpletransform.applyTransformToPoint(simpletransform.invertTransform(viewbox_transform), doc_size)
+
+    default = [doc_size[0] / 2.0, doc_size[1] / 2.0]
+    simpletransform.applyTransformToPoint(viewbox_transform, default)
+    default = Point(*default)
+
+    if len(guides) < 2:
+        return default
+
+    # Find out where the guides intersect.  Only pay attention to the first two.
+    guides = guides[:2]
+
+    lines = []
+    for guide in guides:
+        # inkscape's Y axis is reversed from SVG's, and the guide is in inkscape coordinates
+        position = Point(*_string_to_floats(guide.get('position')))
+        position.y = doc_size[1] - position.y
+
+
+        # This one baffles me.  I think inkscape might have gotten the order of
+        # their vector wrong?
+        parts = _string_to_floats(guide.get('orientation'))
+        direction = Point(parts[1], parts[0])
+
+        # We have a theoretically infinite line defined by a point on the line
+        # and a vector direction.  Shapely can only deal in concrete line
+        # segments, so we'll pick points really far in either direction on the
+        # line and call it good enough.
+        lines.append(shgeo.LineString((position + 100000 * direction, position - 100000 * direction)))
+
+    intersection = lines[0].intersection(lines[1])
+
+    if isinstance(intersection, shgeo.Point):
+        origin = [intersection.x, intersection.y]
+        simpletransform.applyTransformToPoint(viewbox_transform, origin)
+        return Point(*origin)
+    else:
+        # Either the two guides are the same line, or they're parallel.
+        return default
+
+
+def write_embroidery_file(file_path, stitches, svg):
+    origin = get_origin(svg)
 
     pattern = libembroidery.embPattern_create()
     last_color = None
@@ -520,9 +584,9 @@ def write_embroidery_file(file_path, stitches):
             last_color = stitch.color
 
         flags = get_flags(stitch)
-        libembroidery.embPattern_addStitchAbs(pattern, stitch.x - min_x, stitch.y - min_y, flags, 1)
+        libembroidery.embPattern_addStitchAbs(pattern, stitch.x - origin.x, stitch.y - origin.y, flags, 1)
 
-    libembroidery.embPattern_addStitchAbs(pattern, stitch.x - min_x, stitch.y - min_y, libembroidery.END, 1)
+    libembroidery.embPattern_addStitchAbs(pattern, stitch.x - origin.x, stitch.y - origin.y, libembroidery.END, 1)
 
     # convert from pixels to millimeters
     libembroidery.embPattern_scale(pattern, 1/PIXELS_PER_MM)

messages.po

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2018-02-24 20:25-0500\n"
+"POT-Creation-Date: 2018-02-26 19:33-0500\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -312,29 +312,29 @@ msgstr ""
 msgid "Embroidery Simulation"
 msgstr ""
 
-#: inkstitch.py:94
+#: inkstitch.py:95
 #, python-format
 msgid "parseLengthWithUnits: unknown unit %s"
 msgstr ""
 
-#: inkstitch.py:126
+#: inkstitch.py:127
 #, python-format
 msgid "Unknown unit: %s"
 msgstr ""
 
-#: inkstitch.py:329
+#: inkstitch.py:335
 msgid "TRIM after"
 msgstr ""
 
-#: inkstitch.py:330
+#: inkstitch.py:336
 msgid "Trim thread after this object (for supported machines and file formats)"
 msgstr ""
 
-#: inkstitch.py:339
+#: inkstitch.py:345
 msgid "STOP after"
 msgstr ""
 
-#: inkstitch.py:340
+#: inkstitch.py:346
 msgid ""
 "Add STOP instruction after this object (for supported machines and file "
 "formats)"