Initial commit Export Paper Model by emu: T51199 T50357

1 files changed, 2520 insertions, 0 deletions

diff --git a/io_export_paper_model.py b/io_export_paper_model.py
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+++ b/io_export_paper_model.py
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+# -*- coding: utf-8 -*-
+# ##### BEGIN GPL LICENSE BLOCK #####
+#
+#  This program is free software: you can redistribute it and/or modify
+#  it under the terms of the GNU General Public License as published by
+#  the Free Software Foundation, either version 2 of the License, or
+#  (at your option) any later version.
+#
+#  This program is distributed in the hope that it will be useful,
+#  but without any warranty; without even the implied warranty of
+#  merchantability or fitness for a particular purpose.  See the
+#  GNU General Public License for more details.
+#
+#  You should have received a copy of the GNU General Public License
+#  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# ##### END GPL LICENSE BLOCK #####
+
+bl_info = {
+    "name": "Export Paper Model",
+    "author": "Addam Dominec",
+    "version": (0, 9),
+    "blender": (2, 70, 0),
+    "location": "File > Export > Paper Model",
+    "warning": "",
+    "description": "Export printable net of the active mesh",
+    "category": "Import-Export",
+    "wiki_url": "http://wiki.blender.org/index.php/Extensions:2.6/Py/"
+                "Scripts/Import-Export/Paper_Model",
+    "tracker_url": "https://developer.blender.org/T38441"
+}
+
+#### TODO:
+# sanitize the constructors so that they don't edit their parent object
+# rename verts -> vertices, edge.vect -> edge.vector
+# SVG object doesn't need a 'pure_net' argument in constructor
+# remember selected objects before baking, except selected to active
+# islands with default names should be excluded while matching
+# add 'estimated number of pages' to the export UI
+# profile QuickSweepline vs. BruteSweepline with/without blist: for which nets is it faster?
+# rotate islands to minimize area -- and change that only if necessary to fill the page size
+# Sticker.vertices should be of type Vector
+
+# check conflicts in island naming and either:
+#  * append a number to the conflicting names or
+#  * enumerate faces uniquely within all islands of the same name (requires a check that both label and abbr. equals)
+
+
+"""
+
+Additional links:
+    e-mail: adominec {at} gmail {dot} com
+
+"""
+import bpy
+import bl_operators
+import bgl
+import mathutils as M
+from re import compile as re_compile
+from itertools import chain, repeat
+from math import pi, ceil
+
+try:
+    import os.path as os_path
+except ImportError:
+    os_path = None
+
+try:
+    from blist import blist
+except ImportError:
+    blist = list
+
+default_priority_effect = {
+    'CONVEX': 0.5,
+    'CONCAVE': 1,
+    'LENGTH': -0.05
+}
+
+
+def first_letters(text):
+    """Iterator over the first letter of each word"""
+    for match in first_letters.pattern.finditer(text):
+        yield text[match.start()]
+first_letters.pattern = re_compile("((?<!\w)\w)|\d")
+
+
+def is_upsidedown_wrong(name):
+    """Tell if the string would get a different meaning if written upside down"""
+    chars = set(name)
+    mistakable = set("69NZMWpbqd")
+    rotatable = set("80oOxXIl").union(mistakable)
+    return chars.issubset(rotatable) and not chars.isdisjoint(mistakable)
+
+
+def pairs(sequence):
+    """Generate consecutive pairs throughout the given sequence; at last, it gives elements last, first."""
+    i = iter(sequence)
+    previous = first = next(i)
+    for this in i:
+        yield previous, this
+        previous = this
+    yield this, first
+
+
+def argmax_pair(array, key):
+    """Find an (unordered) pair of indices that maximize the given function"""
+    l = len(array)
+    mi, mj, m = None, None, None
+    for i in range(l):
+        for j in range(i+1, l):
+            k = key(array[i], array[j])
+            if not m or k > m:
+                mi, mj, m = i, j, k
+    return mi, mj
+
+
+def fitting_matrix(v1, v2):
+    """Get a matrix that rotates v1 to the same direction as v2"""
+    return (1 / v1.length_squared) * M.Matrix((
+        (v1.x*v2.x + v1.y*v2.y, v1.y*v2.x - v1.x*v2.y),
+        (v1.x*v2.y - v1.y*v2.x, v1.x*v2.x + v1.y*v2.y)))
+
+
+def z_up_matrix(n):
+    """Get a rotation matrix that aligns given vector upwards."""
+    b = n.xy.length
+    l = n.length
+    if b > 0:
+        return M.Matrix((
+            (n.x*n.z/(b*l), n.y*n.z/(b*l), -b/l),
+            (-n.y/b, n.x/b, 0),
+            (0, 0, 0)
+        ))
+    else:
+        # no need for rotation
+        return M.Matrix((
+            (1, 0, 0),
+            (0, (-1 if n.z < 0 else 1), 0),
+            (0, 0, 0)
+        ))
+
+
+def create_blank_image(image_name, dimensions, alpha=1):
+    """Create a new image and assign white color to all its pixels"""
+    image_name = image_name[:64]
+    width, height = int(dimensions.x), int(dimensions.y)
+    image = bpy.data.images.new(image_name, width, height, alpha=True)
+    if image.users > 0:
+        raise UnfoldError("There is something wrong with the material of the model. "
+            "Please report this on the BlenderArtists forum. Export failed.")
+    image.pixels = [1, 1, 1, alpha] * (width * height)
+    image.file_format = 'PNG'
+    return image
+
+
+def bake(face_indices, uvmap, image):
+    import bpy
+    is_cycles = (bpy.context.scene.render.engine == 'CYCLES')
+    if is_cycles:
+        # please excuse the following mess. Cycles baking API does not seem to allow better.
+        ob = bpy.context.active_object
+        me = ob.data
+        mat = bpy.data.materials.new("unfolder dummy")
+        mat.use_nodes = True
+        img = mat.node_tree.nodes.new('ShaderNodeTexImage')
+        img.image = image
+        mat.node_tree.nodes.active = img
+        uv = mat.node_tree.nodes.new('ShaderNodeUVMap')
+        uv.uv_map = uvmap.name
+        mat.node_tree.links.new(uv.outputs['UV'], img.inputs['Vector'])
+        uvmap.active = True
+        recall_object_slots, recall_mesh_slots = [slot.material for slot in ob.material_slots], me.materials[:]
+        for i, slot in enumerate(ob.material_slots):
+            slot.material = me.materials[i] = mat
+        me.materials.append(mat)
+        loop = me.uv_layers[me.uv_layers.active_index].data
+        face_indices = set(face_indices)
+        ignored_uvs = [face.loop_start + i for face in me.polygons if face.index not in face_indices for i, v in enumerate(face.vertices)]
+        for vid in ignored_uvs:
+            loop[vid].uv[0] *= -1
+            loop[vid].uv[1] *= -1
+        bake_type = bpy.context.scene.cycles.bake_type
+        sta = bpy.context.scene.render.bake.use_selected_to_active
+        try:
+            bpy.ops.object.bake(type=bake_type, margin=0, use_selected_to_active=sta, cage_extrusion=100, use_clear=False)
+        except RuntimeError as e:
+            raise UnfoldError(*e.args)
+        finally:
+            me.materials.pop()
+            for slot, recall in zip(ob.material_slots, recall_object_slots):
+                slot.material = recall
+            for i, recall in enumerate(recall_mesh_slots):
+                me.materials[i] = recall
+            bpy.data.materials.remove(mat)
+        for vid in ignored_uvs:
+            loop[vid].uv[0] *= -1
+            loop[vid].uv[1] *= -1
+    else:
+        texfaces = uvmap.data
+        for fid in face_indices:
+            texfaces[fid].image = image
+        bpy.ops.object.bake_image()
+        for fid in face_indices:
+            texfaces[fid].image = None
+
+
+class UnfoldError(ValueError):
+    pass
+
+
+class Unfolder:
+    def __init__(self, ob):
+        self.ob = ob
+        self.mesh = Mesh(ob.data, ob.matrix_world)
+        self.mesh.check_correct()
+        self.tex = None
+
+    def prepare(self, cage_size=None, create_uvmap=False, mark_seams=False, priority_effect=default_priority_effect, scale=1):
+        """Create the islands of the net"""
+        self.mesh.generate_cuts(cage_size / scale if cage_size else None, priority_effect)
+        is_landscape = cage_size and cage_size.x > cage_size.y
+        self.mesh.finalize_islands(is_landscape)
+        self.mesh.enumerate_islands()
+        if create_uvmap:
+            self.tex = self.mesh.save_uv()
+        if mark_seams:
+            self.mesh.mark_cuts()
+
+    def copy_island_names(self, island_list):
+        """Copy island label and abbreviation from the best matching island in the list"""
+        orig_islands = [{face.id for face in item.faces} for item in island_list]
+        matching = list()
+        for i, island in enumerate(self.mesh.islands):
+            islfaces = {uvface.face.index for uvface in island.faces}
+            matching.extend((len(islfaces.intersection(item)), i, j) for j, item in enumerate(orig_islands))
+        matching.sort(reverse=True)
+        available_new = [True for island in self.mesh.islands]
+        available_orig = [True for item in island_list]
+        for face_count, i, j in matching:
+            if available_new[i] and available_orig[j]:
+                available_new[i] = available_orig[j] = False
+                self.mesh.islands[i].label = island_list[j].label
+                self.mesh.islands[i].abbreviation = island_list[j].abbreviation
+
+    def save(self, properties):
+        """Export the document"""
+        # Note about scale: input is direcly in blender length
+        # Mesh.scale_islands multiplies everything by a user-defined ratio
+        # exporters (SVG or PDF) multiply everything by 1000 (output in millimeters)
+        Exporter = SVG if properties.file_format == 'SVG' else PDF
+        filepath = properties.filepath
+        extension = properties.file_format.lower()
+        filepath = bpy.path.ensure_ext(filepath, "." + extension)
+        # page size in meters
+        page_size = M.Vector((properties.output_size_x, properties.output_size_y))
+        # printable area size in meters
+        printable_size = page_size - 2 * properties.output_margin * M.Vector((1, 1))
+        unit_scale = bpy.context.scene.unit_settings.scale_length
+        ppm = properties.output_dpi * 100 / 2.54  # pixels per meter
+
+        # after this call, all dimensions will be in meters
+        self.mesh.scale_islands(unit_scale/properties.scale)
+        if properties.do_create_stickers:
+            self.mesh.generate_stickers(properties.sticker_width, properties.do_create_numbers)
+        elif properties.do_create_numbers:
+            self.mesh.generate_numbers_alone(properties.sticker_width)
+
+        text_height = properties.sticker_width if (properties.do_create_numbers and len(self.mesh.islands) > 1) else 0
+        aspect_ratio = printable_size.x / printable_size.y
+        # title height must be somewhat larger that text size, glyphs go below the baseline
+        self.mesh.finalize_islands(is_landscape=(printable_size.x > printable_size.y), title_height=text_height * 1.2)
+        self.mesh.fit_islands(cage_size=printable_size)
+
+        if properties.output_type != 'NONE':
+            # bake an image and save it as a PNG to disk or into memory
+            image_packing = properties.image_packing if properties.file_format == 'SVG' else 'ISLAND_EMBED'
+            use_separate_images = image_packing in ('ISLAND_LINK', 'ISLAND_EMBED')
+            tex = self.mesh.save_uv(cage_size=printable_size, separate_image=use_separate_images, tex=self.tex)
+            if not tex:
+                raise UnfoldError("The mesh has no UV Map slots left. Either delete a UV Map or export the net without textures.")
+
+            sce = bpy.context.scene
+            rd = sce.render
+            bk = rd.bake
+            if rd.engine == 'CYCLES':
+                recall = sce.cycles.bake_type, bk.use_selected_to_active, bk.margin, bk.cage_extrusion, bk.use_cage, bk.use_clear
+                lookup = {'TEXTURE': 'DIFFUSE_COLOR', 'AMBIENT_OCCLUSION': 'AO', 'RENDER': 'COMBINED', 'SELECTED_TO_ACTIVE': 'COMBINED'}
+                sce.cycles.bake_type = lookup[properties.output_type]
+                bk.use_selected_to_active = (properties.output_type == 'SELECTED_TO_ACTIVE')
+                bk.margin, bk.cage_extrusion, bk.use_cage, bk.use_clear = 0, 10, False, False
+            else:
+                recall = rd.engine, rd.bake_type, rd.use_bake_to_vertex_color, rd.use_bake_selected_to_active, rd.bake_distance, rd.bake_bias, rd.bake_margin, rd.use_bake_clear
+                rd.engine = 'BLENDER_RENDER'
+                lookup = {'TEXTURE': 'TEXTURE', 'AMBIENT_OCCLUSION': 'AO', 'RENDER': 'FULL', 'SELECTED_TO_ACTIVE': 'FULL'}
+                rd.bake_type = lookup[properties.output_type]
+                rd.use_bake_selected_to_active = (properties.output_type == 'SELECTED_TO_ACTIVE')
+                rd.bake_margin, rd.bake_distance, rd.bake_bias, rd.use_bake_to_vertex_color, rd.use_bake_clear = 0, 0, 0.001, False, False
+
+            if image_packing == 'PAGE_LINK':
+                self.mesh.save_image(tex, printable_size * ppm, filepath)
+            elif image_packing == 'ISLAND_LINK':
+                self.mesh.save_separate_images(tex, ppm, filepath)
+            elif image_packing == 'ISLAND_EMBED':
+                self.mesh.save_separate_images(tex, ppm, filepath, embed=Exporter.encode_image)
+
+            # revoke settings
+            if rd.engine == 'CYCLES':
+                sce.cycles.bake_type, bk.use_selected_to_active, bk.margin, bk.cage_extrusion, bk.use_cage, bk.use_clear = recall
+            else:
+                rd.engine, rd.bake_type, rd.use_bake_to_vertex_color, rd.use_bake_selected_to_active, rd.bake_distance, rd.bake_bias, rd.bake_margin, rd.use_bake_clear = recall
+            if not properties.do_create_uvmap:
+                tex.active = True
+                bpy.ops.mesh.uv_texture_remove()
+
+        exporter = Exporter(page_size, properties.style, properties.output_margin, (properties.output_type == 'NONE'), properties.angle_epsilon)
+        exporter.do_create_stickers = properties.do_create_stickers
+        exporter.text_size = properties.sticker_width
+        exporter.write(self.mesh, filepath)
+
+
+class Mesh:
+    """Wrapper for Bpy Mesh"""
+
+    def __init__(self, mesh, matrix):
+        self.verts = dict()
+        self.edges = dict()
+        self.edges_by_verts_indices = dict()
+        self.faces = dict()
+        self.islands = list()
+        self.data = mesh
+        self.pages = list()
+        for bpy_vertex in mesh.vertices:
+            self.verts[bpy_vertex.index] = Vertex(bpy_vertex, matrix)
+        for bpy_edge in mesh.edges:
+            edge = Edge(bpy_edge, self, matrix)
+            self.edges[bpy_edge.index] = edge
+            self.edges_by_verts_indices[(edge.va.index, edge.vb.index)] = edge
+            self.edges_by_verts_indices[(edge.vb.index, edge.va.index)] = edge
+        for bpy_face in mesh.polygons:
+            face = Face(bpy_face, self)
+            self.faces[bpy_face.index] = face
+        for edge in self.edges.values():
+            edge.choose_main_faces()
+            if edge.main_faces:
+                edge.calculate_angle()
+
+    def check_correct(self, epsilon=1e-6):
+        """Check for invalid geometry"""
+        null_edges = {i for i, e in self.edges.items() if e.length < epsilon and e.faces}
+        null_faces = {i for i, f in self.faces.items() if f.normal.length_squared < epsilon}
+        twisted_faces = {i for i, f in self.faces.items() if f.is_twisted()}
+        if not (null_edges or null_faces or twisted_faces):
+            return
+        bpy.context.tool_settings.mesh_select_mode = False, bool(null_edges), bool(null_faces or twisted_faces)
+        for vertex in self.data.vertices:
+            vertex.select = False
+        for edge in self.data.edges:
+            edge.select = (edge.index in null_edges)
+        for face in self.data.polygons:
+            face.select = (face.index in null_faces or face.index in twisted_faces)
+        cure = "Remove Doubles and Triangulate" if (null_edges or null_faces) and twisted_faces else "Triangulate" if twisted_faces else "Remove Doubles"
+        raise UnfoldError("The model contains:\n" +
+            (" {} zero-length edge(s)\n".format(len(null_edges)) if null_edges else "") +
+            (" {} zero-area face(s)\n".format(len(null_faces)) if null_faces else "") +
+            (" {} twisted polygon(s)\n".format(len(twisted_faces)) if twisted_faces else "") +
+            "The offenders are selected and you can use {} to fix them. Export failed.".format(cure))
+
+    def generate_cuts(self, page_size, priority_effect):
+        """Cut the mesh so that it can be unfolded to a flat net."""
+        # warning: this constructor modifies its parameter (face)
+        islands = {Island(face) for face in self.faces.values()}
+        # check for edges that are cut permanently
+        edges = [edge for edge in self.edges.values() if not edge.force_cut and len(edge.faces) > 1]
+
+        if edges:
+            average_length = sum(edge.length for edge in edges) / len(edges)
+            for edge in edges:
+                edge.generate_priority(priority_effect, average_length)
+            edges.sort(reverse=False, key=lambda edge: edge.priority)
+            for edge in edges:
+                if edge.length == 0:
+                    continue
+                face_a, face_b = edge.main_faces
+                island_a, island_b = face_a.uvface.island, face_b.uvface.island
+                if island_a is not island_b:
+                    if len(island_b.faces) > len(island_a.faces):
+                        island_a, island_b = island_b, island_a
+                    if island_a.join(island_b, edge, size_limit=page_size):
+                        islands.remove(island_b)
+
+        self.islands = sorted(islands, reverse=True, key=lambda island: len(island.faces))
+
+        for edge in self.edges.values():
+            # some edges did not know until now whether their angle is convex or concave
+            if edge.main_faces and (edge.main_faces[0].uvface.flipped or edge.main_faces[1].uvface.flipped):
+                edge.calculate_angle()
+            # ensure that the order of faces corresponds to the order of uvedges
+            if edge.main_faces:
+                reordered = [None, None]
+                for uvedge in edge.uvedges:
+                    try:
+                        index = edge.main_faces.index(uvedge.uvface.face)
+                        reordered[index] = uvedge
+                    except ValueError:
+                        reordered.append(uvedge)
+                edge.uvedges = reordered
+
+        for island in self.islands:
+            # if the normals are ambiguous, flip them so that there are more convex edges than concave ones
+            if any(uvface.flipped for uvface in island.faces):
+                island_edges = {uvedge.edge for uvedge in island.edges if not uvedge.edge.is_cut(uvedge.uvface.face)}
+                balance = sum((+1 if edge.angle > 0 else -1) for edge in island_edges)
+                if balance < 0:
+                    island.is_inside_out = True
+
+            # construct a linked list from each island's boundary
+            # uvedge.neighbor_right is clockwise = forward = via uvedge.vb if not uvface.flipped
+            neighbor_lookup, conflicts = dict(), dict()
+            for uvedge in island.boundary:
+                uvvertex = uvedge.va if uvedge.uvface.flipped else uvedge.vb
+                if uvvertex not in neighbor_lookup:
+                    neighbor_lookup[uvvertex] = uvedge
+                else:
+                    if uvvertex not in conflicts:
+                        conflicts[uvvertex] = [neighbor_lookup[uvvertex], uvedge]
+                    else:
+                        conflicts[uvvertex].append(uvedge)
+
+            for uvedge in island.boundary:
+                uvvertex = uvedge.vb if uvedge.uvface.flipped else uvedge.va
+                if uvvertex not in conflicts:
+                    # using the 'get' method so as to handle single-connected vertices properly
+                    uvedge.neighbor_right = neighbor_lookup.get(uvvertex, uvedge)
+                    uvedge.neighbor_right.neighbor_left = uvedge
+                else:
+                    conflicts[uvvertex].append(uvedge)
+
+            # resolve merged vertices with more boundaries crossing
+            def direction_to_float(vector):
+                return (1 - vector.x/vector.length) if vector.y > 0 else (vector.x/vector.length - 1)
+            for uvvertex, uvedges in conflicts.items():
+                def is_inwards(uvedge):
+                    return uvedge.uvface.flipped == (uvedge.va is uvvertex)
+
+                def uvedge_sortkey(uvedge):
+                    if is_inwards(uvedge):
+                        return direction_to_float(uvedge.va.co - uvedge.vb.co)
+                    else:
+                        return direction_to_float(uvedge.vb.co - uvedge.va.co)
+
+                uvedges.sort(key=uvedge_sortkey)
+                for right, left in zip(uvedges[:-1:2], uvedges[1::2]) if is_inwards(uvedges[0]) else zip([uvedges[-1]] + uvedges[1::2], uvedges[:-1:2]):
+                    left.neighbor_right = right
+                    right.neighbor_left = left
+        return True
+
+    def mark_cuts(self):
+        """Mark cut edges in the original mesh so that the user can see"""
+        for bpy_edge in self.data.edges:
+            edge = self.edges[bpy_edge.index]
+            bpy_edge.use_seam = len(edge.uvedges) > 1 and edge.is_main_cut
+
+    def generate_stickers(self, default_width, do_create_numbers=True):
+        """Add sticker faces where they are needed."""
+        def uvedge_priority(uvedge):
+            """Retuns whether it is a good idea to stick something on this edge's face"""
+            # TODO: it should take into account overlaps with faces and with other stickers
+            return uvedge.uvface.face.area / sum((vb.co - va.co).length for (va, vb) in pairs(uvedge.uvface.verts))
+
+        def add_sticker(uvedge, index, target_island):
+            uvedge.sticker = Sticker(uvedge, default_width, index, target_island)
+            uvedge.island.add_marker(uvedge.sticker)
+
+        for edge in self.edges.values():
+            if edge.is_main_cut and len(edge.uvedges) >= 2 and edge.vect.length_squared > 0:
+                uvedge_a, uvedge_b = edge.uvedges[:2]
+                if uvedge_priority(uvedge_a) < uvedge_priority(uvedge_b):
+                    uvedge_a, uvedge_b = uvedge_b, uvedge_a
+                target_island = uvedge_a.island
+                left_edge, right_edge = uvedge_a.neighbor_left.edge, uvedge_a.neighbor_right.edge
+                if do_create_numbers:
+                    for uvedge in [uvedge_b] + edge.uvedges[2:]:
+                        if ((uvedge.neighbor_left.edge is not right_edge or uvedge.neighbor_right.edge is not left_edge) and
+                                uvedge not in (uvedge_a.neighbor_left, uvedge_a.neighbor_right)):
+                            # it will not be clear to see that these uvedges should be sticked together
+                            # So, create an arrow and put the index on all stickers
+                            target_island.sticker_numbering += 1
+                            index = str(target_island.sticker_numbering)
+                            if is_upsidedown_wrong(index):
+                                index += "."
+                            target_island.add_marker(Arrow(uvedge_a, default_width, index))
+                            break
+                    else:
+                        # if all uvedges to be sticked are easy to see, create no numbers
+                        index = None
+                else:
+                    index = None
+                add_sticker(uvedge_b, index, target_island)
+            elif len(edge.uvedges) > 2:
+                index = None
+                target_island = edge.uvedges[0].island
+            if len(edge.uvedges) > 2:
+                for uvedge in edge.uvedges[2:]:
+                    add_sticker(uvedge, index, target_island)
+
+    def generate_numbers_alone(self, size):
+        global_numbering = 0
+        for edge in self.edges.values():
+            if edge.is_main_cut and len(edge.uvedges) >= 2:
+                global_numbering += 1
+                index = str(global_numbering)
+                if is_upsidedown_wrong(index):
+                    index += "."
+                for uvedge in edge.uvedges:
+                    uvedge.island.add_marker(NumberAlone(uvedge, index, size))
+
+    def enumerate_islands(self):
+        for num, island in enumerate(self.islands, 1):
+            island.number = num
+            island.generate_label()
+
+    def scale_islands(self, scale):
+        for island in self.islands:
+            for point in chain((vertex.co for vertex in island.verts), island.fake_verts):
+                point *= scale
+
+    def finalize_islands(self, is_landscape=False, title_height=0):
+        for island in self.islands:
+            if title_height:
+                island.title = "[{}] {}".format(island.abbreviation, island.label)
+            points = list(vertex.co for vertex in island.verts) + island.fake_verts
+            angle = M.geometry.box_fit_2d(points)
+            rot = M.Matrix.Rotation(angle, 2)
+            # ensure that the island matches page orientation (portrait/landscape)
+            dimensions = M.Vector(max(r * v for v in points) - min(r * v for v in points) for r in rot)
+            if dimensions.x > dimensions.y != is_landscape:
+                rot = M.Matrix.Rotation(angle + pi / 2, 2)
+            for point in points:
+                # note: we need an in-place operation, and Vector.rotate() seems to work for 3d vectors only
+                point[:] = rot * point
+            for marker in island.markers:
+                marker.rot = rot * marker.rot
+            bottom_left = M.Vector((min(v.x for v in points), min(v.y for v in points) - title_height))
+            for point in points:
+                point -= bottom_left
+            island.bounding_box = M.Vector((max(v.x for v in points), max(v.y for v in points)))
+
+    def largest_island_ratio(self, page_size):
+        return max(i / p for island in self.islands for (i, p) in zip(island.bounding_box, page_size))
+
+    def fit_islands(self, cage_size):
+        """Move islands so that they fit onto pages, based on their bounding boxes"""
+
+        def try_emplace(island, page_islands, cage_size, stops_x, stops_y, occupied_cache):
+            """Tries to put island to each pair from stops_x, stops_y
+            and checks if it overlaps with any islands present on the page.
+            Returns True and positions the given island on success."""
+            bbox_x, bbox_y = island.bounding_box.xy
+            for x in stops_x:
+                if x + bbox_x > cage_size.x:
+                    continue
+                for y in stops_y:
+                    if y + bbox_y > cage_size.y or (x, y) in occupied_cache:
+                        continue
+                    for i, obstacle in enumerate(page_islands):
+                        # if this obstacle overlaps with the island, try another stop
+                        if (x + bbox_x > obstacle.pos.x and
+                                obstacle.pos.x + obstacle.bounding_box.x > x and
+                                y + bbox_y > obstacle.pos.y and
+                                obstacle.pos.y + obstacle.bounding_box.y > y):
+                            if x >= obstacle.pos.x and y >= obstacle.pos.y:
+                                occupied_cache.add((x, y))
+                            # just a stupid heuristic to make subsequent searches faster
+                            if i > 0:
+                                page_islands[1:i+1] = page_islands[:i]
+                                page_islands[0] = obstacle
+                            break
+                    else:
+                        # if no obstacle called break, this position is okay
+                        island.pos.xy = x, y
+                        page_islands.append(island)
+                        stops_x.append(x + bbox_x)
+                        stops_y.append(y + bbox_y)
+                        return True
+            return False
+
+        def drop_portion(stops, border, divisor):
+            stops.sort()
+            # distance from left neighbor to the right one, excluding the first stop
+            distances = [right - left for left, right in zip(stops, chain(stops[2:], [border]))]
+            quantile = sorted(distances)[len(distances) // divisor]
+            return [stop for stop, distance in zip(stops, chain([quantile], distances)) if distance >= quantile]
+
+        if any(island.bounding_box.x > cage_size.x or island.bounding_box.y > cage_size.y for island in self.islands):
+            raise UnfoldError("An island is too big to fit onto page of the given size. "
+                "Either downscale the model or find and split that island manually.\n"
+                "Export failed, sorry.")
+        # sort islands by their diagonal... just a guess
+        remaining_islands = sorted(self.islands, reverse=True, key=lambda island: island.bounding_box.length_squared)
+        page_num = 1
+
+        while remaining_islands:
+            # create a new page and try to fit as many islands onto it as possible
+            page = Page(page_num)
+            page_num += 1
+            occupied_cache = set()
+            stops_x, stops_y = [0], [0]
+            for island in remaining_islands:
+                try_emplace(island, page.islands, cage_size, stops_x, stops_y, occupied_cache)
+                # if overwhelmed with stops, drop a quarter of them
+                if len(stops_x)**2 > 4 * len(self.islands) + 100:
+                    stops_x = drop_portion(stops_x, cage_size.x, 4)
+                    stops_y = drop_portion(stops_y, cage_size.y, 4)
+            remaining_islands = [island for island in remaining_islands if island not in page.islands]
+            self.pages.append(page)
+
+    def save_uv(self, cage_size=M.Vector((1, 1)), separate_image=False, tex=None):
+        # TODO: mode switching should be handled by higher-level code
+        bpy.ops.object.mode_set()
+        # note: assuming that the active object's data is self.mesh
+        if not tex:
+            tex = self.data.uv_textures.new()
+            if not tex:
+                return None
+        tex.name = "Unfolded"
+        tex.active = True
+        # TODO: this is somewhat dirty, but I do not see a nicer way in the API
+        loop = self.data.uv_layers[self.data.uv_layers.active_index]
+        if separate_image:
+            for island in self.islands:
+                island.save_uv_separate(loop)
+        else:
+            for island in self.islands:
+                island.save_uv(loop, cage_size)
+        return tex
+
+    def save_image(self, tex, page_size_pixels: M.Vector, filename):
+        for page in self.pages:
+            image = create_blank_image("{} {} Unfolded".format(self.data.name[:14], page.name), page_size_pixels, alpha=1)
+            image.filepath_raw = page.image_path = "{}_{}.png".format(filename, page.name)
+            faces = [uvface.face.index for island in page.islands for uvface in island.faces]
+            bake(faces, tex, image)
+            image.save()
+            image.user_clear()
+            bpy.data.images.remove(image)
+
+    def save_separate_images(self, tex, scale, filepath, embed=None):
+        for i, island in enumerate(self.islands, 1):
+            image_name = "{} isl{}".format(self.data.name[:15], i)
+            image = create_blank_image(image_name, island.bounding_box * scale, alpha=0)
+            bake([uvface.face.index for uvface in island.faces], tex, image)
+            if embed:
+                island.embedded_image = embed(image)
+            else:
+                from os import makedirs
+                image_dir = filepath
+                makedirs(image_dir, exist_ok=True)
+                image_path = os_path.join(image_dir, "island{}.png".format(i))
+                image.filepath_raw = image_path
+                image.save()
+                island.image_path = image.path
+            image.user_clear()
+            bpy.data.images.remove(image)
+
+
+class Vertex:
+    """BPy Vertex wrapper"""
+    __slots__ = ('index', 'co', 'edges', 'uvs')
+
+    def __init__(self, bpy_vertex, matrix):
+        self.index = bpy_vertex.index
+        self.co = matrix * bpy_vertex.co
+        self.edges = list()
+        self.uvs = list()
+
+    def __hash__(self):
+        return hash(self.index)
+
+    def __eq__(self, other):
+        return self.index == other.index
+
+
+class Edge:
+    """Wrapper for BPy Edge"""
+    __slots__ = ('va', 'vb', 'faces', 'main_faces', 'uvedges',
+        'vect', 'length', 'angle',
+        'is_main_cut', 'force_cut', 'priority', 'freestyle')
+
+    def __init__(self, edge, mesh, matrix=1):
+        self.va = mesh.verts[edge.vertices[0]]
+        self.vb = mesh.verts[edge.vertices[1]]
+        self.vect = self.vb.co - self.va.co
+        self.length = self.vect.length
+        self.faces = list()
+        # if self.main_faces is set, then self.uvedges[:2] must correspond to self.main_faces, in their order
+        # this constraint is assured at the time of finishing mesh.generate_cuts
+        self.uvedges = list()
+
+        self.force_cut = edge.use_seam  # such edges will always be cut
+        self.main_faces = None  # two faces that may be connected in the island
+        # is_main_cut defines whether the two main faces are connected
+        # all the others will be assumed to be cut
+        self.is_main_cut = True
+        self.priority = None
+        self.angle = None
+        self.freestyle = getattr(edge, "use_freestyle_mark", False) # freestyle edges will be highlighted
+        self.va.edges.append(self)  #FIXME: editing foreign attribute
+        self.vb.edges.append(self)  #FIXME: editing foreign attribute
+
+    def choose_main_faces(self):
+        """Choose two main faces that might get connected in an island"""
+        if len(self.faces) == 2:
+            self.main_faces = self.faces
+        elif len(self.faces) > 2:
+            # find (with brute force) the pair of indices whose faces have the most similar normals
+            i, j = argmax_pair(self.faces, key=lambda a, b: abs(a.normal.dot(b.normal)))
+            self.main_faces = [self.faces[i], self.faces[j]]
+
+    def calculate_angle(self):
+        """Calculate the angle between the main faces"""
+        face_a, face_b = self.main_faces
+        if face_a.normal.length_squared == 0 or face_b.normal.length_squared == 0:
+            self.angle = -3 # just a very sharp angle
+            return
+        # correction if normals are flipped
+        a_is_clockwise = ((face_a.verts.index(self.va) - face_a.verts.index(self.vb)) % len(face_a.verts) == 1)
+        b_is_clockwise = ((face_b.verts.index(self.va) - face_b.verts.index(self.vb)) % len(face_b.verts) == 1)
+        is_equal_flip = True
+        if face_a.uvface and face_b.uvface:
+            a_is_clockwise ^= face_a.uvface.flipped
+            b_is_clockwise ^= face_b.uvface.flipped
+            is_equal_flip = (face_a.uvface.flipped == face_b.uvface.flipped)
+            # TODO: maybe this need not be true in _really_ ugly cases: assert(a_is_clockwise != b_is_clockwise)
+        if a_is_clockwise != b_is_clockwise:
+            if (a_is_clockwise == (face_b.normal.cross(face_a.normal).dot(self.vect) > 0)) == is_equal_flip:
+                # the angle is convex
+                self.angle = face_a.normal.angle(face_b.normal)
+            else:
+                # the angle is concave
+                self.angle = -face_a.normal.angle(face_b.normal)
+        else:
+            # normals are flipped, so we know nothing
+            # so let us assume the angle be convex
+            self.angle = face_a.normal.angle(-face_b.normal)
+
+    def generate_priority(self, priority_effect, average_length):
+        """Calculate the priority value for cutting"""
+        angle = self.angle
+        if angle > 0:
+            self.priority = priority_effect['CONVEX'] * angle / pi
+        else:
+            self.priority = priority_effect['CONCAVE'] * (-angle) / pi
+        self.priority += (self.length / average_length) * priority_effect['LENGTH']
+
+    def is_cut(self, face):
+        """Return False if this edge will the given face to another one in the resulting net
+        (useful for edges with more than two faces connected)"""
+        # Return whether there is a cut between the two main faces
+        if self.main_faces and face in self.main_faces:
+            return self.is_main_cut
+        # All other faces (third and more) are automatically treated as cut
+        else:
+            return True
+
+    def other_uvedge(self, this):
+        """Get an uvedge of this edge that is not the given one
+        causes an IndexError if case of less than two adjacent edges"""
+        return self.uvedges[1] if this is self.uvedges[0] else self.uvedges[0]
+
+
+class Face:
+    """Wrapper for BPy Face"""
+    __slots__ = ('index', 'edges', 'verts', 'uvface',
+        'loop_start', 'area', 'normal')
+
+    def __init__(self, bpy_face, mesh):
+        self.index = bpy_face.index
+        self.edges = list()
+        self.verts = [mesh.verts[i] for i in bpy_face.vertices]
+        self.loop_start = bpy_face.loop_start
+        self.area = bpy_face.area
+        self.uvface = None
+        self.normal = M.geometry.normal(v.co for v in self.verts)
+        for verts_indices in bpy_face.edge_keys:
+            edge = mesh.edges_by_verts_indices[verts_indices]
+            self.edges.append(edge)
+            edge.faces.append(self)  #FIXME: editing foreign attribute
+
+    def is_twisted(self):
+        if len(self.verts) > 3:
+            center = sum((vertex.co for vertex in self.verts), M.Vector((0, 0, 0))) / len(self.verts)
+            plane_d = center.dot(self.normal)
+            diameter = max((center - vertex.co).length for vertex in self.verts)
+            for vertex in self.verts:
+                # check coplanarity
+                if abs(vertex.co.dot(self.normal) - plane_d) > diameter * 0.01:
+                    return True
+        return False
+
+    def __hash__(self):
+        return hash(self.index)
+
+
+class Island:
+    """Part of the net to be exported"""
+    __slots__ = ('faces', 'edges', 'verts', 'fake_verts', 'uvverts_by_id', 'boundary', 'markers',
+        'pos', 'bounding_box',
+        'image_path', 'embedded_image',
+        'number', 'label', 'abbreviation', 'title',
+        'has_safe_geometry', 'is_inside_out',
+        'sticker_numbering')
+
+    def __init__(self, face=None):
+        """Create an Island from a single Face"""
+        self.faces = list()
+        self.edges = set()
+        self.verts = set()
+        self.fake_verts = list()
+        self.markers = list()
+        self.label = None
+        self.abbreviation = None
+        self.title = None
+        self.pos = M.Vector((0, 0))
+        self.image_path = None
+        self.embedded_image = None
+        self.is_inside_out = False  # swaps concave <-> convex edges
+        self.has_safe_geometry = True
+        self.sticker_numbering = 0
+
+        if face:
+            uvface = UVFace(face, self)
+            self.verts.update(uvface.verts)
+            self.edges.update(uvface.edges)
+            self.faces.append(uvface)
+        # speedup for Island.join
+        self.uvverts_by_id = {uvvertex.vertex.index: [uvvertex] for uvvertex in self.verts}
+        # UVEdges on the boundary
+        self.boundary = list(self.edges)
+
+    def join(self, other, edge: Edge, size_limit=None, epsilon=1e-6) -> bool:
+        """
+        Try to join other island on given edge
+        Returns False if they would overlap
+        """
+
+        class Intersection(Exception):
+            pass
+
+        class GeometryError(Exception):
+            pass
+
+        def is_below(self, other, correct_geometry=True):
+            if self is other:
+                return False
+            if self.top < other.bottom:
+                return True
+            if other.top < self.bottom:
+                return False
+            if self.max.tup <= other.min.tup:
+                return True
+            if other.max.tup <= self.min.tup:
+                return False
+            self_vector = self.max.co - self.min.co
+            min_to_min = other.min.co - self.min.co
+            cross_b1 = self_vector.cross(min_to_min)
+            cross_b2 = self_vector.cross(other.max.co - self.min.co)
+            if cross_b2 < cross_b1:
+                cross_b1, cross_b2 = cross_b2, cross_b1
+            if cross_b2 > 0 and (cross_b1 > 0 or (cross_b1 == 0 and not self.is_uvface_upwards())):
+                return True
+            if cross_b1 < 0 and (cross_b2 < 0 or (cross_b2 == 0 and self.is_uvface_upwards())):
+                return False
+            other_vector = other.max.co - other.min.co
+            cross_a1 = other_vector.cross(-min_to_min)
+            cross_a2 = other_vector.cross(self.max.co - other.min.co)
+            if cross_a2 < cross_a1:
+                cross_a1, cross_a2 = cross_a2, cross_a1
+            if cross_a2 > 0 and (cross_a1 > 0 or (cross_a1 == 0 and not other.is_uvface_upwards())):
+                return False
+            if cross_a1 < 0 and (cross_a2 < 0 or (cross_a2 == 0 and other.is_uvface_upwards())):
+                return True
+            if cross_a1 == cross_b1 == cross_a2 == cross_b2 == 0:
+                if correct_geometry:
+                    raise GeometryError
+                elif self.is_uvface_upwards() == other.is_uvface_upwards():
+                    raise Intersection
+                return False
+            if self.min.tup == other.min.tup or self.max.tup == other.max.tup:
+                return cross_a2 > cross_b2
+            raise Intersection
+
+        class QuickSweepline:
+            """Efficient sweepline based on binary search, checking neighbors only"""
+            def __init__(self):
+                self.children = blist()
+
+            def add(self, item, cmp=is_below):
+                low, high = 0, len(self.children)
+                while low < high:
+                    mid = (low + high) // 2
+                    if cmp(self.children[mid], item):
+                        low = mid + 1
+                    else:
+                        high = mid
+                self.children.insert(low, item)
+
+            def remove(self, item, cmp=is_below):
+                index = self.children.index(item)
+                self.children.pop(index)
+                if index > 0 and index < len(self.children):
+                    # check for intersection
+                    if cmp(self.children[index], self.children[index-1]):
+                        raise GeometryError
+
+        class BruteSweepline:
+            """Safe sweepline which checks all its members pairwise"""
+            def __init__(self):
+                self.children = set()
+                self.last_min = None, []
+                self.last_max = None, []
+
+            def add(self, item, cmp=is_below):
+                for child in self.children:
+                    if child.min is not item.min and child.max is not item.max:
+                        cmp(item, child, False)
+                self.children.add(item)
+
+            def remove(self, item):
+                self.children.remove(item)
+
+        def sweep(sweepline, segments):
+            """Sweep across the segments and raise an exception if necessary"""
+            # careful, 'segments' may be a use-once iterator
+            events_add = sorted(segments, reverse=True, key=lambda uvedge: uvedge.min.tup)
+            events_remove = sorted(events_add, reverse=True, key=lambda uvedge: uvedge.max.tup)
+            while events_remove:
+                while events_add and events_add[-1].min.tup <= events_remove[-1].max.tup:
+                    sweepline.add(events_add.pop())
+                sweepline.remove(events_remove.pop())
+
+        def root_find(value, tree):
+            """Find the root of a given value in a forest-like dictionary
+            also updates the dictionary using path compression"""
+            parent, relink = tree.get(value), list()
+            while parent is not None:
+                relink.append(value)
+                value, parent = parent, tree.get(parent)
+            tree.update(dict.fromkeys(relink, value))
+            return value
+
+        def slope_from(position):
+            def slope(uvedge):
+                vec = (uvedge.vb.co - uvedge.va.co) if uvedge.va.tup == position else (uvedge.va.co - uvedge.vb.co)
+                return (vec.y / vec.length + 1) if ((vec.x, vec.y) > (0, 0)) else (-1 - vec.y / vec.length)
+            return slope
+
+        # find edge in other and in self
+        for uvedge in edge.uvedges:
+            if uvedge.uvface.face in uvedge.edge.main_faces:
+                if uvedge.uvface.island is self and uvedge in self.boundary:
+                    uvedge_a = uvedge
+                elif uvedge.uvface.island is other and uvedge in other.boundary:
+                    uvedge_b = uvedge
+                else:
+                    return False
+
+        # check if vertices and normals are aligned correctly
+        verts_flipped = uvedge_b.va.vertex is uvedge_a.va.vertex
+        flipped = verts_flipped ^ uvedge_a.uvface.flipped ^ uvedge_b.uvface.flipped
+        # determine rotation
+        # NOTE: if the edges differ in length, the matrix will involve uniform scaling.
+        # Such situation may occur in the case of twisted n-gons
+        first_b, second_b = (uvedge_b.va, uvedge_b.vb) if not verts_flipped else (uvedge_b.vb, uvedge_b.va)
+        if not flipped:
+            rot = fitting_matrix(first_b.co - second_b.co, uvedge_a.vb.co - uvedge_a.va.co)
+        else:
+            flip = M.Matrix(((-1, 0), (0, 1)))
+            rot = fitting_matrix(flip * (first_b.co - second_b.co), uvedge_a.vb.co - uvedge_a.va.co) * flip
+        trans = uvedge_a.vb.co - rot * first_b.co
+        # extract and transform island_b's boundary
+        phantoms = {uvvertex: UVVertex(rot*uvvertex.co + trans, uvvertex.vertex) for uvvertex in other.verts}
+
+        # check the size of the resulting island
+        if size_limit:
+            # first check: bounding box
+            bbox_width = max(max(seg.max.co.x for seg in self.boundary), max(vertex.co.x for vertex in phantoms)) - min(min(seg.min.co.x for seg in self.boundary), min(vertex.co.x for vertex in phantoms))
+            bbox_height = max(max(seg.top for seg in self.boundary), max(vertex.co.y for vertex in phantoms)) - min(min(seg.bottom for seg in self.boundary), min(vertex.co.y for vertex in phantoms))
+            if min(bbox_width, bbox_height)**2 > size_limit.x**2 + size_limit.y**2:
+                return False
+            if (bbox_width > size_limit.x or bbox_height > size_limit.y) and (bbox_height > size_limit.x or bbox_width > size_limit.y):
+                # further checks (TODO!)
+                # for the time being, just throw this piece away
+                return False
+
+        distance_limit = edge.vect.length_squared * epsilon
+        # try and merge UVVertices closer than sqrt(distance_limit)
+        merged_uvedges = set()
+        merged_uvedge_pairs = list()
+
+        # merge all uvvertices that are close enough using a union-find structure
+        # uvvertices will be merged only in cases other->self and self->self
+        # all resulting groups are merged together to a uvvertex of self
+        is_merged_mine = False
+        shared_vertices = self.uvverts_by_id.keys() & other.uvverts_by_id.keys()
+        for vertex_id in shared_vertices:
+            uvs = self.uvverts_by_id[vertex_id] + other.uvverts_by_id[vertex_id]
+            len_mine = len(self.uvverts_by_id[vertex_id])
+            merged = dict()
+            for i, a in enumerate(uvs[:len_mine]):
+                i = root_find(i, merged)
+                for j, b in enumerate(uvs[i+1:], i+1):
+                    b = b if j < len_mine else phantoms[b]
+                    j = root_find(j, merged)
+                    if i == j:
+                        continue
+                    i, j = (j, i) if j < i else (i, j)
+                    if (a.co - b.co).length_squared < distance_limit:
+                        merged[j] = i
+            for source, target in merged.items():
+                target = root_find(target, merged)
+                phantoms[uvs[source]] = uvs[target]
+                is_merged_mine |= (source < len_mine)  # remember that a vertex of this island has been merged
+
+        for uvedge in (chain(self.boundary, other.boundary) if is_merged_mine else other.boundary):
+            for partner in uvedge.edge.uvedges:
+                if partner is not uvedge:
+                    paired_a, paired_b = phantoms.get(partner.vb, partner.vb), phantoms.get(partner.va, partner.va)
+                    if (partner.uvface.flipped ^ flipped) != uvedge.uvface.flipped:
+                        paired_a, paired_b = paired_b, paired_a
+                    if phantoms.get(uvedge.va, uvedge.va) is paired_a and phantoms.get(uvedge.vb, uvedge.vb) is paired_b:
+                        # if these two edges will get merged, add them both to the set
+                        merged_uvedges.update((uvedge, partner))
+                        merged_uvedge_pairs.append((uvedge, partner))
+                        break
+
+        if uvedge_b not in merged_uvedges:
+            raise UnfoldError("Export failed. Please report this error, including the model if you can.")
+
+        boundary_other = [PhantomUVEdge(phantoms[uvedge.va], phantoms[uvedge.vb], flipped ^ uvedge.uvface.flipped)
+            for uvedge in other.boundary if uvedge not in merged_uvedges]
+        # TODO: if is_merged_mine, it might make sense to create a similar list from self.boundary as well
+
+        incidence = {vertex.tup for vertex in phantoms.values()}.intersection(vertex.tup for vertex in self.verts)
+        incidence = {position: list() for position in incidence}  # from now on, 'incidence' is a dict
+        for uvedge in chain(boundary_other, self.boundary):
+            if uvedge.va.co == uvedge.vb.co:
+                continue
+            for vertex in (uvedge.va, uvedge.vb):
+                site = incidence.get(vertex.tup)
+                if site is not None:
+                    site.append(uvedge)
+        for position, segments in incidence.items():
+            if len(segments) <= 2:
+                continue
+            segments.sort(key=slope_from(position))
+            for right, left in pairs(segments):
+                is_left_ccw = left.is_uvface_upwards() ^ (left.max.tup == position)
+                is_right_ccw = right.is_uvface_upwards() ^ (right.max.tup == position)
+                if is_right_ccw and not is_left_ccw and type(right) is not type(left) and right not in merged_uvedges and left not in merged_uvedges:
+                    return False
+                if (not is_right_ccw and right not in merged_uvedges) ^ (is_left_ccw and left not in merged_uvedges):
+                    return False
+
+        # check for self-intersections
+        try:
+            try:
+                sweepline = QuickSweepline() if self.has_safe_geometry and other.has_safe_geometry else BruteSweepline()
+                sweep(sweepline, (uvedge for uvedge in chain(boundary_other, self.boundary)))
+                self.has_safe_geometry &= other.has_safe_geometry
+            except GeometryError:
+                sweep(BruteSweepline(), (uvedge for uvedge in chain(boundary_other, self.boundary)))
+                self.has_safe_geometry = False
+        except Intersection:
+            return False
+
+        # mark all edges that connect the islands as not cut
+        for uvedge in merged_uvedges:
+            uvedge.edge.is_main_cut = False
+
+        # include all trasformed vertices as mine
+        self.verts.update(phantoms.values())
+
+        # update the uvverts_by_id dictionary
+        for source, target in phantoms.items():
+            present = self.uvverts_by_id.get(target.vertex.index)
+            if not present:
+                self.uvverts_by_id[target.vertex.index] = [target]
+            else:
+                # emulation of set behavior... sorry, it is faster
+                if source in present:
+                    present.remove(source)
+                if target not in present:
+                    present.append(target)
+
+        # re-link uvedges and uvfaces to their transformed locations
+        for uvedge in other.edges:
+            uvedge.island = self
+            uvedge.va = phantoms[uvedge.va]
+            uvedge.vb = phantoms[uvedge.vb]
+            uvedge.update()
+        if is_merged_mine:
+            for uvedge in self.edges:
+                uvedge.va = phantoms.get(uvedge.va, uvedge.va)
+                uvedge.vb = phantoms.get(uvedge.vb, uvedge.vb)
+        self.edges.update(other.edges)
+
+        for uvface in other.faces:
+            uvface.island = self
+            uvface.verts = [phantoms[uvvertex] for uvvertex in uvface.verts]
+            uvface.uvvertex_by_id = {index: phantoms[uvvertex]
+                for index, uvvertex in uvface.uvvertex_by_id.items()}
+            uvface.flipped ^= flipped
+        if is_merged_mine:
+            # there may be own uvvertices that need to be replaced by phantoms
+            for uvface in self.faces:
+                if any(uvvertex in phantoms for uvvertex in uvface.verts):
+                    uvface.verts = [phantoms.get(uvvertex, uvvertex) for uvvertex in uvface.verts]
+                    uvface.uvvertex_by_id = {index: phantoms.get(uvvertex, uvvertex)
+                        for index, uvvertex in uvface.uvvertex_by_id.items()}
+        self.faces.extend(other.faces)
+
+        self.boundary = [uvedge for uvedge in
+            chain(self.boundary, other.boundary) if uvedge not in merged_uvedges]
+
+        for uvedge, partner in merged_uvedge_pairs:
+            # make sure that main faces are the ones actually merged (this changes nothing in most cases)
+            uvedge.edge.main_faces[:] = uvedge.uvface.face, partner.uvface.face
+
+        # everything seems to be OK
+        return True
+
+    def add_marker(self, marker):
+        self.fake_verts.extend(marker.bounds)
+        self.markers.append(marker)
+
+    def generate_label(self, label=None, abbreviation=None):
+        """Assign a name to this island automatically"""
+        abbr = abbreviation or self.abbreviation or str(self.number)
+        # TODO: dots should be added in the last instant when outputting any text
+        if is_upsidedown_wrong(abbr):
+            abbr += "."
+        self.label = label or self.label or "Island {}".format(self.number)
+        self.abbreviation = abbr
+
+    def save_uv(self, tex, cage_size):
+        """Save UV Coordinates of all UVFaces to a given UV texture
+        tex: UV Texture layer to use (BPy MeshUVLoopLayer struct)
+        page_size: size of the page in pixels (vector)"""
+        texface = tex.data
+        for uvface in self.faces:
+            for i, uvvertex in enumerate(uvface.verts):
+                uv = uvvertex.co + self.pos
+                texface[uvface.face.loop_start + i].uv[0] = uv.x / cage_size.x
+                texface[uvface.face.loop_start + i].uv[1] = uv.y / cage_size.y
+
+    def save_uv_separate(self, tex):
+        """Save UV Coordinates of all UVFaces to a given UV texture, spanning from 0 to 1
+        tex: UV Texture layer to use (BPy MeshUVLoopLayer struct)
+        page_size: size of the page in pixels (vector)"""
+        texface = tex.data
+        scale_x, scale_y = 1 / self.bounding_box.x, 1 / self.bounding_box.y
+        for uvface in self.faces:
+            for i, uvvertex in enumerate(uvface.verts):
+                texface[uvface.face.loop_start + i].uv[0] = uvvertex.co.x * scale_x
+                texface[uvface.face.loop_start + i].uv[1] = uvvertex.co.y * scale_y
+
+
+class Page:
+    """Container for several Islands"""
+    __slots__ = ('islands', 'name', 'image_path')
+
+    def __init__(self, num=1):
+        self.islands = list()
+        self.name = "page{}".format(num)
+        self.image_path = None
+
+
+class UVVertex:
+    """Vertex in 2D"""
+    __slots__ = ('co', 'vertex', 'tup')
+
+    def __init__(self, vector, vertex=None):
+        self.co = vector.xy
+        self.vertex = vertex
+        self.tup = tuple(self.co)
+
+    def __repr__(self):
+        if self.vertex:
+            return "UV {} [{:.3f}, {:.3f}]".format(self.vertex.index, self.co.x, self.co.y)
+        else:
+            return "UV * [{:.3f}, {:.3f}]".format(self.co.x, self.co.y)
+
+
+class UVEdge:
+    """Edge in 2D"""
+    # Every UVEdge is attached to only one UVFace
+    # UVEdges are doubled as needed because they both have to point clockwise around their faces
+    __slots__ = ('va', 'vb', 'island', 'uvface', 'edge',
+        'min', 'max', 'bottom', 'top',
+        'neighbor_left', 'neighbor_right', 'sticker')
+
+    def __init__(self, vertex1: UVVertex, vertex2: UVVertex, island: Island, uvface, edge):
+        self.va = vertex1
+        self.vb = vertex2
+        self.update()
+        self.island = island
+        self.uvface = uvface
+        self.sticker = None
+        self.edge = edge
+
+    def update(self):
+        """Update data if UVVertices have moved"""
+        self.min, self.max = (self.va, self.vb) if (self.va.tup < self.vb.tup) else (self.vb, self.va)
+        y1, y2 = self.va.co.y, self.vb.co.y
+        self.bottom, self.top = (y1, y2) if y1 < y2 else (y2, y1)
+
+    def is_uvface_upwards(self):
+        return (self.va.tup < self.vb.tup) ^ self.uvface.flipped
+
+    def __repr__(self):
+        return "({0.va} - {0.vb})".format(self)
+
+
+class PhantomUVEdge:
+    """Temporary 2D Segment for calculations"""
+    __slots__ = ('va', 'vb', 'min', 'max', 'bottom', 'top')
+
+    def __init__(self, vertex1: UVVertex, vertex2: UVVertex, flip):
+        self.va, self.vb = (vertex2, vertex1) if flip else (vertex1, vertex2)
+        self.min, self.max = (self.va, self.vb) if (self.va.tup < self.vb.tup) else (self.vb, self.va)
+        y1, y2 = self.va.co.y, self.vb.co.y
+        self.bottom, self.top = (y1, y2) if y1 < y2 else (y2, y1)
+
+    def is_uvface_upwards(self):
+        return self.va.tup < self.vb.tup
+
+    def __repr__(self):
+        return "[{0.va} - {0.vb}]".format(self)
+
+
+class UVFace:
+    """Face in 2D"""
+    __slots__ = ('verts', 'edges', 'face', 'island', 'flipped', 'uvvertex_by_id')
+
+    def __init__(self, face: Face, island: Island):
+        """Creace an UVFace from a Face and a fixed edge.
+        face: Face to take coordinates from
+        island: Island to register itself in
+        fixed_edge: Edge to connect to (that already has UV coordinates)"""
+        self.verts = list()
+        self.face = face
+        face.uvface = self
+        self.island = island
+        self.flipped = False  # a flipped UVFace has edges clockwise
+
+        rot = z_up_matrix(face.normal)
+        self.uvvertex_by_id = {vertex.index: UVVertex(rot * vertex.co, vertex) for vertex in face.verts}
+        self.verts = [self.uvvertex_by_id[vertex.index] for vertex in face.verts]
+        self.edges = list()
+        edge_by_verts = dict()
+        for edge in face.edges:
+            edge_by_verts[(edge.va.index, edge.vb.index)] = edge
+            edge_by_verts[(edge.vb.index, edge.va.index)] = edge
+        for va, vb in pairs(self.verts):
+            edge = edge_by_verts[(va.vertex.index, vb.vertex.index)]
+            uvedge = UVEdge(va, vb, island, self, edge)
+            self.edges.append(uvedge)
+            edge.uvedges.append(uvedge)  #FIXME: editing foreign attribute
+
+
+class Arrow:
+    """Mark in the document: an arrow denoting the number of the edge it points to"""
+    __slots__ = ('bounds', 'center', 'rot', 'text', 'size')
+
+    def __init__(self, uvedge, size, index):
+        self.text = str(index)
+        edge = (uvedge.vb.co - uvedge.va.co) if not uvedge.uvface.flipped else (uvedge.va.co - uvedge.vb.co)
+        self.center = (uvedge.va.co + uvedge.vb.co) / 2
+        self.size = size
+        sin, cos = edge.y / edge.length, edge.x / edge.length
+        self.rot = M.Matrix(((cos, -sin), (sin, cos)))
+        tangent = edge.normalized()
+        normal = M.Vector((tangent.y, -tangent.x))
+        self.bounds = [self.center, self.center + (1.2*normal + tangent)*size, self.center + (1.2*normal - tangent)*size]
+
+
+class Sticker:
+    """Mark in the document: sticker tab"""
+    __slots__ = ('bounds', 'center', 'rot', 'text', 'width', 'vertices')
+
+    def __init__(self, uvedge, default_width=0.005, index=None, target_island=None):
+        """Sticker is directly attached to the given UVEdge"""
+        first_vertex, second_vertex = (uvedge.va, uvedge.vb) if not uvedge.uvface.flipped else (uvedge.vb, uvedge.va)
+        edge = first_vertex.co - second_vertex.co
+        sticker_width = min(default_width, edge.length / 2)
+        other = uvedge.edge.other_uvedge(uvedge)  # This is the other uvedge - the sticking target
+
+        other_first, other_second = (other.va, other.vb) if not other.uvface.flipped else (other.vb, other.va)
+        other_edge = other_second.co - other_first.co
+
+        # angle a is at vertex uvedge.va, b is at uvedge.vb
+        cos_a = cos_b = 0.5
+        sin_a = sin_b = 0.75**0.5
+        # len_a is length of the side adjacent to vertex a, len_b likewise
+        len_a = len_b = sticker_width / sin_a
+
+        # fix overlaps with the most often neighbour - its sticking target
+        if first_vertex == other_second:
+            cos_a = max(cos_a, (edge*other_edge) / (edge.length**2))  # angles between pi/3 and 0
+        elif second_vertex == other_first:
+            cos_b = max(cos_b, (edge*other_edge) / (edge.length**2))  # angles between pi/3 and 0
+
+        # Fix tabs for sticking targets with small angles
+        # Index of other uvedge in its face (not in its island)
+        other_idx = other.uvface.edges.index(other)
+        # Left and right neighbors in the face
+        other_face_neighbor_left = other.uvface.edges[(other_idx+1) % len(other.uvface.edges)]
+        other_face_neighbor_right = other.uvface.edges[(other_idx-1) % len(other.uvface.edges)]
+        other_edge_neighbor_a = other_face_neighbor_left.vb.co - other.vb.co
+        other_edge_neighbor_b = other_face_neighbor_right.va.co - other.va.co
+        # Adjacent angles in the face
+        cos_a = max(cos_a, (-other_edge*other_edge_neighbor_a) / (other_edge.length*other_edge_neighbor_a.length))
+        cos_b = max(cos_b, (other_edge*other_edge_neighbor_b) / (other_edge.length*other_edge_neighbor_b.length))
+
+        # Calculate the lengths of the glue tab edges using the possibly smaller angles
+        sin_a = abs(1 - cos_a**2)**0.5
+        len_b = min(len_a, (edge.length*sin_a) / (sin_a*cos_b + sin_b*cos_a))
+        len_a = 0 if sin_a == 0 else min(sticker_width / sin_a, (edge.length - len_b*cos_b) / cos_a)
+
+        sin_b = abs(1 - cos_b**2)**0.5
+        len_a = min(len_a, (edge.length*sin_b) / (sin_a*cos_b + sin_b*cos_a))
+        len_b = 0 if sin_b == 0 else min(sticker_width / sin_b, (edge.length - len_a*cos_a) / cos_b)
+
+        v3 = UVVertex(second_vertex.co + M.Matrix(((cos_b, -sin_b), (sin_b, cos_b))) * edge *len_b / edge.length)
+        v4 = UVVertex(first_vertex.co + M.Matrix(((-cos_a, -sin_a), (sin_a, -cos_a))) * edge * len_a / edge.length)
+        if v3.co != v4.co:
+            self.vertices = [second_vertex, v3, v4, first_vertex]
+        else:
+            self.vertices = [second_vertex, v3, first_vertex]
+
+        sin, cos = edge.y / edge.length, edge.x / edge.length
+        self.rot = M.Matrix(((cos, -sin), (sin, cos)))
+        self.width = sticker_width * 0.9
+        if index and target_island is not uvedge.island:
+            self.text = "{}:{}".format(target_island.abbreviation, index)
+        else:
+            self.text = index
+        self.center = (uvedge.va.co + uvedge.vb.co) / 2 + self.rot*M.Vector((0, self.width*0.2))
+        self.bounds = [v3.co, v4.co, self.center] if v3.co != v4.co else [v3.co, self.center]
+
+
+class NumberAlone:
+    """Mark in the document: numbering inside the island denoting edges to be sticked"""
+    __slots__ = ('bounds', 'center', 'rot', 'text', 'size')
+
+    def __init__(self, uvedge, index, default_size=0.005):
+        """Sticker is directly attached to the given UVEdge"""
+        edge = (uvedge.va.co - uvedge.vb.co) if not uvedge.uvface.flipped else (uvedge.vb.co - uvedge.va.co)
+
+        self.size = default_size
+        sin, cos = edge.y / edge.length, edge.x / edge.length
+        self.rot = M.Matrix(((cos, -sin), (sin, cos)))
+        self.text = index
+        self.center = (uvedge.va.co + uvedge.vb.co) / 2 - self.rot*M.Vector((0, self.size*1.2))
+        self.bounds = [self.center]
+
+
+class SVG:
+    """Simple SVG exporter"""
+
+    def __init__(self, page_size: M.Vector, style, margin, pure_net=True, angle_epsilon=0.01):
+        """Initialize document settings.
+        page_size: document dimensions in meters
+        pure_net: if True, do not use image"""
+        self.page_size = page_size
+        self.pure_net = pure_net
+        self.style = style
+        self.margin = margin
+        self.text_size = 12
+        self.angle_epsilon = angle_epsilon
+
+    @classmethod
+    def encode_image(cls, bpy_image):
+        import tempfile
+        import base64
+        with tempfile.TemporaryDirectory() as directory:
+            filename = directory + "/i.png"
+            bpy_image.filepath_raw = filename
+            bpy_image.save()
+            return base64.encodebytes(open(filename, "rb").read()).decode('ascii')
+
+    def format_vertex(self, vector, pos=M.Vector((0, 0))):
+        """Return a string with both coordinates of the given vertex."""
+        x, y = vector + pos
+        return "{:.6f} {:.6f}".format((x + self.margin) * 1000, (self.page_size.y - y - self.margin) * 1000)
+
+    def write(self, mesh, filename):
+        """Write data to a file given by its name."""
+        line_through = " L ".join  # used for formatting of SVG path data
+        rows = "\n".join
+
+        dl = ["{:.2f}".format(length * self.style.line_width * 1000) for length in (2, 5, 10)]
+        format_style = {'SOLID': "none", 'DOT': "{0},{1}".format(*dl), 'DASH': "{1},{2}".format(*dl), 'LONGDASH': "{2},{1}".format(*dl), 'DASHDOT': "{2},{1},{0},{1}".format(*dl)}
+
+        def format_color(vec):
+            return "#{:02x}{:02x}{:02x}".format(round(vec[0] * 255), round(vec[1] * 255), round(vec[2] * 255))
+
+        def format_matrix(matrix):
+            return " ".join("{:.6f}".format(cell) for column in matrix for cell in column)
+
+        def path_convert(string, relto=os_path.dirname(filename)):
+            assert(os_path)  # check the module was imported
+            string = os_path.relpath(string, relto)
+            if os_path.sep != '/':
+                string = string.replace(os_path.sep, '/')
+            return string
+
+        styleargs = {name: format_color(getattr(self.style, name)) for name in
+            ("outer_color", "outbg_color", "convex_color", "concave_color", "freestyle_color",
+            "inbg_color", "sticker_fill", "text_color")}
+        styleargs.update({name: format_style[getattr(self.style, name)] for name in
+            ("outer_style", "convex_style", "concave_style", "freestyle_style")})
+        styleargs.update({name: getattr(self.style, attr)[3] for name, attr in
+            (("outer_alpha", "outer_color"), ("outbg_alpha", "outbg_color"),
+            ("convex_alpha", "convex_color"), ("concave_alpha", "concave_color"),
+            ("freestyle_alpha", "freestyle_color"),
+            ("inbg_alpha", "inbg_color"), ("sticker_alpha", "sticker_fill"),
+            ("text_alpha", "text_color"))})
+        styleargs.update({name: getattr(self.style, name) * self.style.line_width * 1000 for name in
+            ("outer_width", "convex_width", "concave_width", "freestyle_width", "outbg_width", "inbg_width")})
+        for num, page in enumerate(mesh.pages):
+            page_filename = "{}_{}.svg".format(filename[:filename.rfind(".svg")], page.name) if len(mesh.pages) > 1 else filename
+            with open(page_filename, 'w') as f:
+                print(self.svg_base.format(width=self.page_size.x*1000, height=self.page_size.y*1000), file=f)
+                print(self.css_base.format(**styleargs), file=f)
+                if page.image_path:
+                    print(self.image_linked_tag.format(
+                        pos="{0:.6f} {0:.6f}".format(self.margin*1000),
+                        width=(self.page_size.x - 2 * self.margin)*1000,
+                        height=(self.page_size.y - 2 * self.margin)*1000,
+                        path=path_convert(page.image_path)),
+                        file=f)
+                if len(page.islands) > 1:
+                    print("<g>", file=f)
+
+                for island in page.islands:
+                    print("<g>", file=f)
+                    if island.image_path:
+                        print(self.image_linked_tag.format(
+                            pos=self.format_vertex(island.pos + M.Vector((0, island.bounding_box.y))),
+                            width=island.bounding_box.x*1000,
+                            height=island.bounding_box.y*1000,
+                            path=path_convert(island.image_path)),
+                            file=f)
+                    elif island.embedded_image:
+                        print(self.image_embedded_tag.format(
+                                pos=self.format_vertex(island.pos + M.Vector((0, island.bounding_box.y))),
+                                width=island.bounding_box.x*1000,
+                                height=island.bounding_box.y*1000,
+                                path=island.image_path),
+                            island.embedded_image, "'/>",
+                            file=f, sep="")
+                    if island.title:
+                        print(self.text_tag.format(
+                            size=1000 * self.text_size,
+                            x=1000 * (island.bounding_box.x*0.5 + island.pos.x + self.margin),
+                            y=1000 * (self.page_size.y - island.pos.y - self.margin - 0.2 * self.text_size),
+                            label=island.title), file=f)
+
+                    data_markers, data_stickerfill, data_outer, data_convex, data_concave, data_freestyle = (list() for i in range(6))
+                    for marker in island.markers:
+                        if isinstance(marker, Sticker):
+                            data_stickerfill.append("M {} Z".format(
+                                line_through(self.format_vertex(vertex.co, island.pos) for vertex in marker.vertices)))
+                            if marker.text:
+                                data_markers.append(self.text_transformed_tag.format(
+                                    label=marker.text,
+                                    pos=self.format_vertex(marker.center, island.pos),
+                                    mat=format_matrix(marker.rot),
+                                    size=marker.width * 1000))
+                        elif isinstance(marker, Arrow):
+                            size = marker.size * 1000
+                            position = marker.center + marker.rot*marker.size*M.Vector((0, -0.9))
+                            data_markers.append(self.arrow_marker_tag.format(
+                                index=marker.text,
+                                arrow_pos=self.format_vertex(marker.center, island.pos),
+                                scale=size,
+                                pos=self.format_vertex(position, island.pos - marker.size*M.Vector((0, 0.4))),
+                                mat=format_matrix(size * marker.rot)))
+                        elif isinstance(marker, NumberAlone):
+                            data_markers.append(self.text_transformed_tag.format(
+                                label=marker.text,
+                                pos=self.format_vertex(marker.center, island.pos),
+                                mat=format_matrix(marker.rot),
+                                size=marker.size * 1000))
+                    if data_stickerfill and self.style.sticker_fill[3] > 0:
+                        print("<path class='sticker' d='", rows(data_stickerfill), "'/>", file=f)
+
+                    outer_edges = set(island.boundary)
+                    while outer_edges:
+                        data_loop = list()
+                        uvedge = outer_edges.pop()
+                        while 1:
+                            if uvedge.sticker:
+                                data_loop.extend(self.format_vertex(vertex.co, island.pos) for vertex in uvedge.sticker.vertices[1:])
+                            else:
+                                vertex = uvedge.vb if uvedge.uvface.flipped else uvedge.va
+                                data_loop.append(self.format_vertex(vertex.co, island.pos))
+                            uvedge = uvedge.neighbor_right
+                            try:
+                                outer_edges.remove(uvedge)
+                            except KeyError:
+                                break
+                        data_outer.append("M {} Z".format(line_through(data_loop)))
+
+                    for uvedge in island.edges:
+                        edge = uvedge.edge
+                        if edge.is_cut(uvedge.uvface.face) and not uvedge.sticker:
+                            continue
+                        data_uvedge = "M {}".format(
+                            line_through(self.format_vertex(vertex.co, island.pos) for vertex in (uvedge.va, uvedge.vb)))
+                        if edge.freestyle:
+                            data_freestyle.append(data_uvedge)
+                        # each uvedge is in two opposite-oriented variants; we want to add each only once
+                        if uvedge.sticker or uvedge.uvface.flipped != (uvedge.va.vertex.index > uvedge.vb.vertex.index):
+                            if edge.angle > self.angle_epsilon:
+                                data_convex.append(data_uvedge)
+                            elif edge.angle < -self.angle_epsilon:
+                                data_concave.append(data_uvedge)
+                    if island.is_inside_out:
+                        data_convex, data_concave = data_concave, data_convex
+
+                    if data_freestyle:
+                        print("<path class='freestyle' d='", rows(data_freestyle), "'/>", file=f)
+                    if (data_convex or data_concave) and not self.pure_net and self.style.use_inbg:
+                        print("<path class='inner_background' d='", rows(data_convex + data_concave), "'/>", file=f)
+                    if data_convex:
+                        print("<path class='convex' d='", rows(data_convex), "'/>", file=f)
+                    if data_concave:
+                        print("<path class='concave' d='", rows(data_concave), "'/>", file=f)
+                    if data_outer:
+                        if not self.pure_net and self.style.use_outbg:
+                            print("<path class='outer_background' d='", rows(data_outer), "'/>", file=f)
+                        print("<path class='outer' d='", rows(data_outer), "'/>", file=f)
+                    if data_markers:
+                        print(rows(data_markers), file=f)
+                    print("</g>", file=f)
+
+                if len(page.islands) > 1:
+                    print("</g>", file=f)
+                print("</svg>", file=f)
+
+    image_linked_tag = "<image transform='translate({pos})' width='{width:.6f}' height='{height:.6f}' xlink:href='{path}'/>"
+    image_embedded_tag = "<image transform='translate({pos})' width='{width:.6f}' height='{height:.6f}' xlink:href='data:image/png;base64,"
+    text_tag = "<text transform='translate({x} {y})' style='font-size:{size:.2f}'><tspan>{label}</tspan></text>"
+    text_transformed_tag = "<text transform='matrix({mat} {pos})' style='font-size:{size:.2f}'><tspan>{label}</tspan></text>"
+    arrow_marker_tag = "<g><path transform='matrix({mat} {arrow_pos})' class='arrow' d='M 0 0 L 1 1 L 0 0.25 L -1 1 Z'/>" \
+        "<text transform='translate({pos})' style='font-size:{scale:.2f}'><tspan>{index}</tspan></text></g>"
+
+    svg_base = """<?xml version='1.0' encoding='UTF-8' standalone='no'?>
+    <svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' version='1.1'
+    width='{width:.2f}mm' height='{height:.2f}mm' viewBox='0 0 {width:.2f} {height:.2f}'>"""
+
+    css_base = """<style type="text/css">
+    path {{
+        fill: none;
+        stroke-linecap: butt;
+        stroke-linejoin: bevel;
+        stroke-dasharray: none;
+    }}
+    path.outer {{
+        stroke: {outer_color};
+        stroke-dasharray: {outer_style};
+        stroke-dashoffset: 0;
+        stroke-width: {outer_width:.2};
+        stroke-opacity: {outer_alpha:.2};
+    }}
+    path.convex {{
+        stroke: {convex_color};
+        stroke-dasharray: {convex_style};
+        stroke-dashoffset:0;
+        stroke-width:{convex_width:.2};
+        stroke-opacity: {convex_alpha:.2}
+    }}
+    path.concave {{
+        stroke: {concave_color};
+        stroke-dasharray: {concave_style};
+        stroke-dashoffset: 0;
+        stroke-width: {concave_width:.2};
+        stroke-opacity: {concave_alpha:.2}
+    }}
+    path.freestyle {{
+        stroke: {freestyle_color};
+        stroke-dasharray: {freestyle_style};
+        stroke-dashoffset: 0;
+        stroke-width: {freestyle_width:.2};
+        stroke-opacity: {freestyle_alpha:.2}
+    }}
+    path.outer_background {{
+        stroke: {outbg_color};
+        stroke-opacity: {outbg_alpha};
+        stroke-width: {outbg_width:.2}
+    }}
+    path.inner_background {{
+        stroke: {inbg_color};
+        stroke-opacity: {inbg_alpha};
+        stroke-width: {inbg_width:.2}
+    }}
+    path.sticker {{
+        fill: {sticker_fill};
+        stroke: none;
+        fill-opacity: {sticker_alpha:.2};
+    }}
+    path.arrow {{
+        fill: #000;
+    }}
+    text {{
+        font-style: normal;
+        fill: {text_color};
+        fill-opacity: {text_alpha:.2};
+        stroke: none;
+    }}
+    text, tspan {{
+        text-anchor:middle;
+    }}
+    </style>"""
+
+
+class PDF:
+    """Simple PDF exporter"""
+
+    mm_to_pt = 72 / 25.4
+    def __init__(self, page_size: M.Vector, style, margin, pure_net=True, angle_epsilon=0.01):
+        self.page_size = page_size
+        self.style = style
+        self.margin = M.Vector((margin, margin))
+        self.pure_net = pure_net
+        self.angle_epsilon = angle_epsilon
+
+    character_width_packed = {833: 'mM', 834: '¼½¾', 260: '¦|', 389: '*', 584: '>~+¬±<×÷=', 778: 'ÒGÖÕQÔØÓO', 333: '¹\xad\x98\x84²¨\x94\x9b¯¡´()\x8b\x93¸³-\x88`r', 334: '{}', 400: '°', 722: 'DÛÚUÑwRÐÜCÇNÙH', 611: '¿øTßZF\x8e', 469: '^', 278: 'ì\x05\x06 ;\x01/\x08I\x07,\x13\x11\x04\\.![\x15\r\x10:\x18]\x0c\x00\x1bÍf\xa0\x14\x1c\n\t\x1e\x1dïí\x12·\x16\x0bî\x0e\x03tÏ\x17\x1fÎ\x19\x0f\x02Ì\x1a', 537: '¶', 667: 'ÄË\x8aÃÀBÊVX&AKSÈÞPÁYÉ\x9fÝEÅÂ', 222: 'jl\x92\x91i\x82', 737: '©®', 355: '"', 1000: '\x89\x97\x8c\x99\x85Æ', 556: 'éhòúd»§ùþ5\x803õ¢åëûa64_ã\x83ñ¤8n?g2e#9«oqL$âö1päuð\x86¥µ\x967üóê\x87bá0àèô£', 365: 'º', 944: '\x9cW', 370: 'ª', 500: 'Js\x9eçyÿ\x9aývckzx', 350: '\x90\x8d\x81\x8f\x95\x7f\x9d', 1015: '@', 889: 'æ%', 191: "'"}
+    character_width = {c: value for (value, chars) in character_width_packed.items() for c in chars}
+    def text_width(self, text, scale=None):
+        return (scale or self.text_size) * sum(self.character_width.get(c, 556) for c in text) / 1000
+
+    @classmethod
+    def encode_image(cls, bpy_image):
+        data = bytes(int(255 * px) for (i, px) in enumerate(bpy_image.pixels) if i % 4 != 3)
+        image = {"Type": "XObject", "Subtype": "Image", "Width": bpy_image.size[0], "Height": bpy_image.size[1], "ColorSpace": "DeviceRGB", "BitsPerComponent": 8, "Interpolate": True, "Filter": ["ASCII85Decode", "FlateDecode"], "stream": data}
+        return image
+
+
+    def write(self, mesh, filename):
+        def format_dict(obj, refs=tuple()):
+            return "<< " + "".join("/{} {}\n".format(key, format_value(value, refs)) for (key, value) in obj.items()) + ">>"
+
+        def line_through(seq):
+            return "".join("{0.x:.6f} {0.y:.6f} {1} ".format(1000*v.co, c) for (v, c) in zip(seq, chain("m", repeat("l"))))
+
+        def format_value(value, refs=tuple()):
+            if value in refs:
+                return "{} 0 R".format(refs.index(value) + 1)
+            elif type(value) is dict:
+                return format_dict(value, refs)
+            elif type(value) in (list, tuple):
+                return "[ " + " ".join(format_value(item, refs) for item in value) + " ]"
+            elif type(value) is int:
+                return str(value)
+            elif type(value) is float:
+                return "{:.6f}".format(value)
+            elif type(value) is bool:
+                return "true" if value else "false"
+            else:
+                return "/{}".format(value)  # this script can output only PDF names, no strings
+
+        def write_object(index, obj, refs, f, stream=None):
+            byte_count = f.write("{} 0 obj\n".format(index))
+            if type(obj) is not dict:
+                stream, obj = obj, dict()
+            elif "stream" in obj:
+                stream = obj.pop("stream")
+            if stream:
+                if True or type(stream) is bytes:
+                    obj["Filter"] = ["ASCII85Decode", "FlateDecode"]
+                    stream = encode(stream)
+                obj["Length"] = len(stream)
+            byte_count += f.write(format_dict(obj, refs))
+            if stream:
+                byte_count += f.write("\nstream\n")
+                byte_count += f.write(stream)
+                byte_count += f.write("\nendstream")
+            return byte_count + f.write("\nendobj\n")
+
+        def encode(data):
+            from base64 import a85encode
+            from zlib import compress
+            if hasattr(data, "encode"):
+                data = data.encode()
+            return a85encode(compress(data), adobe=True, wrapcol=250)[2:].decode()
+
+        page_size_pt = 1000 * self.mm_to_pt * self.page_size
+        root = {"Type": "Pages", "MediaBox": [0, 0, page_size_pt.x, page_size_pt.y], "Kids": list()}
+        catalog = {"Type": "Catalog", "Pages": root}
+        font = {"Type": "Font", "Subtype": "Type1", "Name": "F1", "BaseFont": "Helvetica", "Encoding": "MacRomanEncoding"}
+
+        dl = [length * self.style.line_width * 1000 for length in (1, 4, 9)]
+        format_style = {'SOLID': list(), 'DOT': [dl[0], dl[1]], 'DASH': [dl[1], dl[2]], 'LONGDASH': [dl[2], dl[1]], 'DASHDOT': [dl[2], dl[1], dl[0], dl[1]]}
+        styles = {
+            "Gtext": {"ca": self.style.text_color[3], "Font": [font, 1000 * self.text_size]},
+            "Gsticker": {"ca": self.style.sticker_fill[3]}}
+        for name in ("outer", "convex", "concave", "freestyle"):
+            gs = {
+                "LW": self.style.line_width * 1000 * getattr(self.style, name + "_width"),
+                "CA": getattr(self.style, name + "_color")[3],
+                "D": [format_style[getattr(self.style, name + "_style")], 0]}
+            styles["G" + name] = gs
+        for name in ("outbg", "inbg"):
+            gs = {
+                "LW": self.style.line_width * 1000 * getattr(self.style, name + "_width"),
+                "CA": getattr(self.style, name + "_color")[3],
+                "D": [format_style['SOLID'], 0]}
+            styles["G" + name] = gs
+
+        objects = [root, catalog, font]
+        objects.extend(styles.values())
+
+        for page in mesh.pages:
+            commands = ["{0:.6f} 0 0 {0:.6f} 0 0 cm".format(self.mm_to_pt)]
+            resources = {"Font": {"F1": font}, "ExtGState": styles, "XObject": dict()}
+            for island in page.islands:
+                commands.append("q 1 0 0 1 {0.x:.6f} {0.y:.6f} cm".format(1000*(self.margin + island.pos)))
+                if island.embedded_image:
+                    identifier = "Im{}".format(len(resources["XObject"]) + 1)
+                    commands.append("q {0.x:.6f} 0 0 {0.y:.6f} 0 0 cm 1 0 0 -1 0 1 cm /{1} Do Q".format(1000 * island.bounding_box, identifier))
+                    objects.append(island.embedded_image)
+                    resources["XObject"][identifier] = island.embedded_image
+
+                if island.title:
+                    commands.append("/Gtext gs BT {x:.6f} {y:.6f} Td ({label}) Tj ET".format(
+                        size=1000*self.text_size,
+                        x=500 * (island.bounding_box.x - self.text_width(island.title)),
+                        y=1000 * 0.2 * self.text_size,
+                        label=island.title))
+
+                data_markers, data_stickerfill, data_outer, data_convex, data_concave, data_freestyle = (list() for i in range(6))
+                for marker in island.markers:
+                    if isinstance(marker, Sticker):
+                        data_stickerfill.append(line_through(marker.vertices) + "f")
+                        if marker.text:
+                            data_markers.append("q {mat[0][0]:.6f} {mat[1][0]:.6f} {mat[0][1]:.6f} {mat[1][1]:.6f} {pos.x:.6f} {pos.y:.6f} cm BT {align:.6f} 0 Td /F1 {size:.6f} Tf ({label}) Tj ET Q".format(
+                                label=marker.text,
+                                pos=1000*marker.center,
+                                mat=marker.rot,
+                                align=-500 * self.text_width(marker.text, marker.width),
+                                size=1000*marker.width))
+                    elif isinstance(marker, Arrow):
+                        size = 1000 * marker.size
+                        position = 1000 * (marker.center + marker.rot*marker.size*M.Vector((0, -0.9)))
+                        data_markers.append("q BT {pos.x:.6f} {pos.y:.6f} Td /F1 {size:.6f} Tf ({index}) Tj ET {mat[0][0]:.6f} {mat[1][0]:.6f} {mat[0][1]:.6f} {mat[1][1]:.6f} {arrow_pos.x:.6f} {arrow_pos.y:.6f} cm 0 0 m 1 -1 l 0 -0.25 l -1 -1 l f Q".format(
+                            index=marker.text,
+                            arrow_pos=1000 * marker.center,
+                            pos=position - 1000 * M.Vector((0.5 * self.text_width(marker.text), 0.4 * self.text_size)),
+                            mat=size * marker.rot,
+                            size=size))
+                    elif isinstance(marker, NumberAlone):
+                        data_markers.append("q {mat[0][0]:.6f} {mat[1][0]:.6f} {mat[0][1]:.6f} {mat[1][1]:.6f} {pos.x:.6f} {pos.y:.6f} cm BT /F1 {size:.6f} Tf ({label}) Tj ET Q".format(
+                            label=marker.text,
+                            pos=1000*marker.center,
+                            mat = marker.rot,
+                            size=1000*marker.size))
+
+                outer_edges = set(island.boundary)
+                while outer_edges:
+                    data_loop = list()
+                    uvedge = outer_edges.pop()
+                    while 1:
+                        if uvedge.sticker:
+                            data_loop.extend(uvedge.sticker.vertices[1:])
+                        else:
+                            vertex = uvedge.vb if uvedge.uvface.flipped else uvedge.va
+                            data_loop.append(vertex)
+                        uvedge = uvedge.neighbor_right
+                        try:
+                            outer_edges.remove(uvedge)
+                        except KeyError:
+                            break
+                    data_outer.append(line_through(data_loop) + "s")
+
+                for uvedge in island.edges:
+                    edge = uvedge.edge
+                    if edge.is_cut(uvedge.uvface.face) and not uvedge.sticker:
+                        continue
+                    data_uvedge = line_through((uvedge.va, uvedge.vb)) + "S"
+                    if edge.freestyle:
+                        data_freestyle.append(data_uvedge)
+                    # each uvedge is in two opposite-oriented variants; we want to add each only once
+                    if uvedge.sticker or uvedge.uvface.flipped != (uvedge.va.vertex.index > uvedge.vb.vertex.index):
+                        if edge.angle > self.angle_epsilon:
+                            data_convex.append(data_uvedge)
+                        elif edge.angle < -self.angle_epsilon:
+                            data_concave.append(data_uvedge)
+                if island.is_inside_out:
+                    data_convex, data_concave = data_concave, data_convex
+
+                if data_stickerfill and self.style.sticker_fill[3] > 0:
+                    commands.append("/Gsticker gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} rg".format(self.style.sticker_fill))
+                    commands.extend(data_stickerfill)
+                if data_freestyle:
+                    commands.append("/Gfreestyle gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} RG".format(self.style.freestyle_color))
+                    commands.extend(data_freestyle)
+                if (data_convex or data_concave) and not self.pure_net and self.style.use_inbg:
+                    commands.append("/Ginbg gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} RG".format(self.style.inbg_color))
+                    commands.extend(chain(data_convex, data_concave))
+                if data_convex:
+                    commands.append("/Gconvex gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} RG".format(self.style.convex_color))
+                    commands.extend(data_convex)
+                if data_concave:
+                    commands.append("/Gconcave gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} RG".format(self.style.concave_color))
+                    commands.extend(data_concave)
+                if data_outer:
+                    if not self.pure_net and self.style.use_outbg:
+                        commands.append("/Goutbg gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} RG".format(self.style.outbg_color))
+                        commands.extend(data_outer)
+                    commands.append("/Gouter gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} RG".format(self.style.outer_color))
+                    commands.extend(data_outer)
+                commands.append("/Gtext gs {0[0]:.3f} {0[1]:.3f} {0[2]:.3f} rg".format(self.style.text_color))
+                commands.extend(data_markers)
+                commands.append("Q")
+            content = "\n".join(commands)
+            page = {"Type": "Page", "Parent": root, "Contents": content, "Resources": resources}
+            root["Kids"].append(page)
+            objects.extend((page, content))
+
+        root["Count"] = len(root["Kids"])
+        with open(filename, "w+") as f:
+            xref_table = list()
+            position = f.write("%PDF-1.4\n")
+            for index, obj in enumerate(objects, 1):
+                xref_table.append(position)
+                position += write_object(index, obj, objects, f)
+            xref_pos = position
+            f.write("xref_table\n0 {}\n".format(len(xref_table) + 1))
+            f.write("{:010} {:05} f\n".format(0, 65536))
+            for position in xref_table:
+                f.write("{:010} {:05} n\n".format(position, 0))
+            f.write("trailer\n")
+            f.write(format_dict({"Size": len(xref_table), "Root": catalog}, objects))
+            f.write("\nstartxref\n{}\n%%EOF\n".format(xref_pos))
+
+
+class Unfold(bpy.types.Operator):
+    """Blender Operator: unfold the selected object."""
+
+    bl_idname = "mesh.unfold"
+    bl_label = "Unfold"
+    bl_description = "Mark seams so that the mesh can be exported as a paper model"
+    bl_options = {'REGISTER', 'UNDO'}
+    edit = bpy.props.BoolProperty(name="", description="", default=False, options={'HIDDEN'})
+    priority_effect_convex = bpy.props.FloatProperty(name="Priority Convex",
+        description="Priority effect for edges in convex angles",
+        default=default_priority_effect['CONVEX'], soft_min=-1, soft_max=10, subtype='FACTOR')
+    priority_effect_concave = bpy.props.FloatProperty(name="Priority Concave",
+        description="Priority effect for edges in concave angles",
+        default=default_priority_effect['CONCAVE'], soft_min=-1, soft_max=10, subtype='FACTOR')
+    priority_effect_length = bpy.props.FloatProperty(name="Priority Length",
+        description="Priority effect of edge length",
+        default=default_priority_effect['LENGTH'], soft_min=-10, soft_max=1, subtype='FACTOR')
+    do_create_uvmap = bpy.props.BoolProperty(name="Create UVMap",
+        description="Create a new UV Map showing the islands and page layout", default=False)
+    object = None
+
+    @classmethod
+    def poll(cls, context):
+        return context.active_object and context.active_object.type == "MESH"
+
+    def draw(self, context):
+        layout = self.layout
+        col = layout.column()
+        col.active = not self.object or len(self.object.data.uv_textures) < 8
+        col.prop(self.properties, "do_create_uvmap")
+        layout.label(text="Edge Cutting Factors:")
+        col = layout.column(align=True)
+        col.label(text="Face Angle:")
+        col.prop(self.properties, "priority_effect_convex", text="Convex")
+        col.prop(self.properties, "priority_effect_concave", text="Concave")
+        layout.prop(self.properties, "priority_effect_length", text="Edge Length")
+
+    def execute(self, context):
+        sce = bpy.context.scene
+        settings = sce.paper_model
+        recall_mode = context.object.mode
+        bpy.ops.object.mode_set(mode='OBJECT')
+        recall_display_islands, sce.paper_model.display_islands = sce.paper_model.display_islands, False
+
+        self.object = context.active_object
+        mesh = self.object.data
+
+        cage_size = M.Vector((settings.output_size_x, settings.output_size_y)) if settings.limit_by_page else None
+        priority_effect = {'CONVEX': self.priority_effect_convex, 'CONCAVE': self.priority_effect_concave, 'LENGTH': self.priority_effect_length}
+        try:
+            unfolder = Unfolder(self.object)
+            unfolder.prepare(cage_size, self.do_create_uvmap, mark_seams=True, priority_effect=priority_effect, scale=sce.unit_settings.scale_length/settings.scale)
+        except UnfoldError as error:
+            self.report(type={'ERROR_INVALID_INPUT'}, message=error.args[0])
+            bpy.ops.object.mode_set(mode=recall_mode)
+            sce.paper_model.display_islands = recall_display_islands
+            return {'CANCELLED'}
+        if mesh.paper_island_list:
+            unfolder.copy_island_names(mesh.paper_island_list)
+
+        island_list = mesh.paper_island_list
+        attributes = {item.label: (item.abbreviation, item.auto_label, item.auto_abbrev) for item in island_list}
+        island_list.clear()  # remove previously defined islands
+        for island in unfolder.mesh.islands:
+            # add islands to UI list and set default descriptions
+            list_item = island_list.add()
+            # add faces' IDs to the island
+            for uvface in island.faces:
+                lface = list_item.faces.add()
+                lface.id = uvface.face.index
+
+            list_item["label"] = island.label
+            list_item["abbreviation"], list_item["auto_label"], list_item["auto_abbrev"] = attributes.get(island.label, (island.abbreviation, True, True))
+            island_item_changed(list_item, context)
+
+        mesh.paper_island_index = -1
+        mesh.show_edge_seams = True
+
+        bpy.ops.object.mode_set(mode=recall_mode)
+        sce.paper_model.display_islands = recall_display_islands
+        return {'FINISHED'}
+
+
+class ClearAllSeams(bpy.types.Operator):
+    """Blender Operator: clear all seams of the active Mesh and all its unfold data"""
+
+    bl_idname = "mesh.clear_all_seams"
+    bl_label = "Clear All Seams"
+    bl_description = "Clear all the seams and unfolded islands of the active object"
+
+    @classmethod
+    def poll(cls, context):
+        return context.active_object and context.active_object.type == 'MESH'
+
+    def execute(self, context):
+        ob = context.active_object
+        mesh = ob.data
+
+        for edge in mesh.edges:
+            edge.use_seam = False
+        mesh.paper_island_list.clear()
+
+        return {'FINISHED'}
+
+
+def page_size_preset_changed(self, context):
+    """Update the actual document size to correct values"""
+    if self.page_size_preset == 'A4':
+        self.output_size_x = 0.210
+        self.output_size_y = 0.297
+    elif self.page_size_preset == 'A3':
+        self.output_size_x = 0.297
+        self.output_size_y = 0.420
+    elif self.page_size_preset == 'US_LETTER':
+        self.output_size_x = 0.216
+        self.output_size_y = 0.279
+    elif self.page_size_preset == 'US_LEGAL':
+        self.output_size_x = 0.216
+        self.output_size_y = 0.356
+
+
+class PaperModelStyle(bpy.types.PropertyGroup):
+    line_styles = [
+        ('SOLID', "Solid (----)", "Solid line"),
+        ('DOT', "Dots (. . .)", "Dotted line"),
+        ('DASH', "Short Dashes (- - -)", "Solid line"),
+        ('LONGDASH', "Long Dashes (-- --)", "Solid line"),
+        ('DASHDOT', "Dash-dotted (-- .)", "Solid line")
+    ]
+    outer_color = bpy.props.FloatVectorProperty(name="Outer Lines",
+        description="Color of net outline",
+        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
+    outer_style = bpy.props.EnumProperty(name="Outer Lines Drawing Style",
+        description="Drawing style of net outline",
+        default='SOLID', items=line_styles)
+    line_width = bpy.props.FloatProperty(name="Base Lines Thickness",
+        description="Base thickness of net lines, each actual value is a multiple of this length",
+        default=1e-4, min=0, soft_max=5e-3, precision=5, step=1e-2, subtype="UNSIGNED", unit="LENGTH")
+    outer_width = bpy.props.FloatProperty(name="Outer Lines Thickness",
+        description="Relative thickness of net outline",
+        default=3, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
+    use_outbg = bpy.props.BoolProperty(name="Highlight Outer Lines",
+        description="Add another line below every line to improve contrast",
+        default=True)
+    outbg_color = bpy.props.FloatVectorProperty(name="Outer Highlight",
+        description="Color of the highlight for outer lines",
+        default=(1.0, 1.0, 1.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
+    outbg_width = bpy.props.FloatProperty(name="Outer Highlight Thickness",
+        description="Relative thickness of the highlighting lines",
+        default=5, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
+
+    convex_color = bpy.props.FloatVectorProperty(name="Inner Convex Lines",
+        description="Color of lines to be folded to a convex angle",
+        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
+    convex_style = bpy.props.EnumProperty(name="Convex Lines Drawing Style",
+        description="Drawing style of lines to be folded to a convex angle",
+        default='DASH', items=line_styles)
+    convex_width = bpy.props.FloatProperty(name="Convex Lines Thickness",
+        description="Relative thickness of concave lines",
+        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
+    concave_color = bpy.props.FloatVectorProperty(name="Inner Concave Lines",
+        description="Color of lines to be folded to a concave angle",
+        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
+    concave_style = bpy.props.EnumProperty(name="Concave Lines Drawing Style",
+        description="Drawing style of lines to be folded to a concave angle",
+        default='DASHDOT', items=line_styles)
+    concave_width = bpy.props.FloatProperty(name="Concave Lines Thickness",
+        description="Relative thickness of concave lines",
+        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
+    freestyle_color = bpy.props.FloatVectorProperty(name="Freestyle Edges",
+        description="Color of lines marked as Freestyle Edge",
+        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
+    freestyle_style = bpy.props.EnumProperty(name="Freestyle Edges Drawing Style",
+        description="Drawing style of Freestyle Edges",
+        default='SOLID', items=line_styles)
+    freestyle_width = bpy.props.FloatProperty(name="Freestyle Edges Thickness",
+        description="Relative thickness of Freestyle edges",
+        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
+    use_inbg = bpy.props.BoolProperty(name="Highlight Inner Lines",
+        description="Add another line below every line to improve contrast",
+        default=True)
+    inbg_color = bpy.props.FloatVectorProperty(name="Inner Highlight",
+        description="Color of the highlight for inner lines",
+        default=(1.0, 1.0, 1.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
+    inbg_width = bpy.props.FloatProperty(name="Inner Highlight Thickness",
+        description="Relative thickness of the highlighting lines",
+        default=2, min=0, soft_max=10, precision=1, step=10, subtype='FACTOR')
+
+    sticker_fill = bpy.props.FloatVectorProperty(name="Tabs Fill",
+        description="Fill color of sticking tabs",
+        default=(0.9, 0.9, 0.9, 1.0), min=0, max=1, subtype='COLOR', size=4)
+    text_color = bpy.props.FloatVectorProperty(name="Text Color",
+        description="Color of all text used in the document",
+        default=(0.0, 0.0, 0.0, 1.0), min=0, max=1, subtype='COLOR', size=4)
+bpy.utils.register_class(PaperModelStyle)
+
+
+class ExportPaperModel(bpy.types.Operator):
+    """Blender Operator: save the selected object's net and optionally bake its texture"""
+
+    def scaled_getter(name):
+        return lambda self: self[name] / bpy.context.scene.unit_settings.scale_length
+
+    def scaled_setter(name):
+        def setter(self, value):
+            self[name] = value * bpy.context.scene.unit_settings.scale_length
+        return setter
+
+    bl_idname = "export_mesh.paper_model"
+    bl_label = "Export Paper Model"
+    bl_description = "Export the selected object's net and optionally bake its texture"
+    filepath = bpy.props.StringProperty(name="File Path",
+        description="Target file to save the SVG", options={'SKIP_SAVE'})
+    filename = bpy.props.StringProperty(name="File Name",
+        description="Name of the file", options={'SKIP_SAVE'})
+    directory = bpy.props.StringProperty(name="Directory",
+        description="Directory of the file", options={'SKIP_SAVE'})
+    page_size_preset = bpy.props.EnumProperty(name="Page Size",
+        description="Size of the exported document",
+        default='A4', update=page_size_preset_changed, items=[
+            ('USER', "User defined", "User defined paper size"),
+            ('A4', "A4", "International standard paper size"),
+            ('A3', "A3", "International standard paper size"),
+            ('US_LETTER', "Letter", "North American paper size"),
+            ('US_LEGAL', "Legal", "North American paper size")
+        ])
+    output_size_x = bpy.props.FloatProperty(name="Page Width",
+        description="Width of the exported document",
+        default=0.210, soft_min=0.105, soft_max=0.841, subtype="UNSIGNED", unit="LENGTH")
+    output_size_y = bpy.props.FloatProperty(name="Page Height",
+        description="Height of the exported document",
+        default=0.297, soft_min=0.148, soft_max=1.189, subtype="UNSIGNED", unit="LENGTH")
+    output_margin = bpy.props.FloatProperty(name="Page Margin",
+        description="Distance from page borders to the printable area",
+        default=0.005, min=0, soft_max=0.1, step=0.1, subtype="DISTANCE", unit="LENGTH", get=scaled_getter("output_margin"), set=scaled_setter("output_margin"))
+    output_type = bpy.props.EnumProperty(name="Textures",
+        description="Source of a texture for the model",
+        default='NONE', items=[
+            ('NONE', "No Texture", "Export the net only"),
+            ('TEXTURE', "From Materials", "Render the diffuse color and all painted textures"),
+            ('AMBIENT_OCCLUSION', "Ambient Occlusion", "Render the Ambient Occlusion pass"),
+            ('RENDER', "Full Render", "Render the material in actual scene illumination"),
+            ('SELECTED_TO_ACTIVE', "Selected to Active", "Render all selected surrounding objects as a texture")
+        ])
+    do_create_stickers = bpy.props.BoolProperty(name="Create Tabs",
+        description="Create gluing tabs around the net (useful for paper)",
+        default=True)
+    do_create_numbers = bpy.props.BoolProperty(name="Create Numbers",
+        description="Enumerate edges to make it clear which edges should be sticked together",
+        default=True)
+    sticker_width = bpy.props.FloatProperty(name="Tabs and Text Size",
+        description="Width of gluing tabs and their numbers",
+        default=0.005, soft_min=0, soft_max=0.05, step=0.1, subtype="UNSIGNED", unit="LENGTH")
+    angle_epsilon = bpy.props.FloatProperty(name="Hidden Edge Angle",
+        description="Folds with angle below this limit will not be drawn",
+        default=pi/360, min=0, soft_max=pi/4, step=0.01, subtype="ANGLE", unit="ROTATION")
+    output_dpi = bpy.props.FloatProperty(name="Resolution (DPI)",
+        description="Resolution of images in pixels per inch",
+        default=90, min=1, soft_min=30, soft_max=600, subtype="UNSIGNED")
+    file_format = bpy.props.EnumProperty(name="Document Format",
+        description="File format of the exported net",
+        default='PDF', items=[
+            ('PDF', "PDF", "Adobe Portable Document Format 1.4"),
+            ('SVG', "SVG", "W3C Scalable Vector Graphics"),
+        ])
+    image_packing = bpy.props.EnumProperty(name="Image Packing Method",
+        description="Method of attaching baked image(s) to the SVG",
+        default='ISLAND_EMBED', items=[
+            ('PAGE_LINK', "Single Linked", "Bake one image per page of output and save it separately"),
+            ('ISLAND_LINK', "Linked", "Bake images separately for each island and save them in a directory"),
+            ('ISLAND_EMBED', "Embedded", "Bake images separately for each island and embed them into the SVG")
+        ])
+    scale = bpy.props.FloatProperty(name="Scale",
+        description="Divisor of all dimensions when exporting",
+        default=1, soft_min=1.0, soft_max=10000.0, step=100, subtype='UNSIGNED', precision=1)
+    do_create_uvmap = bpy.props.BoolProperty(name="Create UVMap",
+        description="Create a new UV Map showing the islands and page layout",
+        default=False, options={'SKIP_SAVE'})
+    ui_expanded_document = bpy.props.BoolProperty(name="Show Document Settings Expanded",
+        description="Shows the box 'Document Settings' expanded in user interface",
+        default=True, options={'SKIP_SAVE'})
+    ui_expanded_style = bpy.props.BoolProperty(name="Show Style Settings Expanded",
+        description="Shows the box 'Colors and Style' expanded in user interface",
+        default=False, options={'SKIP_SAVE'})
+    style = bpy.props.PointerProperty(type=PaperModelStyle)
+
+    unfolder = None
+    largest_island_ratio = 0
+
+    @classmethod
+    def poll(cls, context):
+        return context.active_object and context.active_object.type == 'MESH'
+
+    def execute(self, context):
+        try:
+            if self.object.data.paper_island_list:
+                self.unfolder.copy_island_names(self.object.data.paper_island_list)
+            self.unfolder.save(self.properties)
+            self.report({'INFO'}, "Saved a {}-page document".format(len(self.unfolder.mesh.pages)))
+            return {'FINISHED'}
+        except UnfoldError as error:
+            self.report(type={'ERROR_INVALID_INPUT'}, message=error.args[0])
+            return {'CANCELLED'}
+        except:
+            raise
+
+    def get_scale_ratio(self, sce):
+        margin = self.output_margin + self.sticker_width + 1e-5
+        if min(self.output_size_x, self.output_size_y) <= 2 * margin:
+            return False
+        output_inner_size = M.Vector((self.output_size_x - 2*margin, self.output_size_y - 2*margin))
+        ratio = self.unfolder.mesh.largest_island_ratio(output_inner_size)
+        return ratio * sce.unit_settings.scale_length / self.scale
+
+    def invoke(self, context, event):
+        sce = context.scene
+        recall_mode = context.object.mode
+        bpy.ops.object.mode_set(mode='OBJECT')
+
+        self.scale = sce.paper_model.scale
+        self.object = context.active_object
+        cage_size = M.Vector((sce.paper_model.output_size_x, sce.paper_model.output_size_y)) if sce.paper_model.limit_by_page else None
+        try:
+            self.unfolder = Unfolder(self.object)
+            self.unfolder.prepare(cage_size, create_uvmap=self.do_create_uvmap, scale=sce.unit_settings.scale_length/self.scale)
+        except UnfoldError as error:
+            self.report(type={'ERROR_INVALID_INPUT'}, message=error.args[0])
+            bpy.ops.object.mode_set(mode=recall_mode)
+            return {'CANCELLED'}
+        scale_ratio = self.get_scale_ratio(sce)
+        if scale_ratio > 1:
+            self.scale = ceil(self.scale * scale_ratio)
+        wm = context.window_manager
+        wm.fileselect_add(self)
+
+        bpy.ops.object.mode_set(mode=recall_mode)
+        return {'RUNNING_MODAL'}
+
+    def draw(self, context):
+        layout = self.layout
+
+        layout.prop(self.properties, "do_create_uvmap")
+
+        row = layout.row(align=True)
+        row.menu("VIEW3D_MT_paper_model_presets", text=bpy.types.VIEW3D_MT_paper_model_presets.bl_label)
+        row.operator("export_mesh.paper_model_preset_add", text="", icon='ZOOMIN')
+        row.operator("export_mesh.paper_model_preset_add", text="", icon='ZOOMOUT').remove_active = True
+
+        # a little hack: this prints out something like "Scale: 1: 72"
+        layout.prop(self.properties, "scale", text="Scale: 1")
+        scale_ratio = self.get_scale_ratio(context.scene)
+        if scale_ratio > 1:
+            layout.label(text="An island is roughly {:.1f}x bigger than page".format(scale_ratio), icon="ERROR")
+        elif scale_ratio > 0:
+            layout.label(text="Largest island is roughly 1/{:.1f} of page".format(1 / scale_ratio))
+
+        box = layout.box()
+        row = box.row(align=True)
+        row.prop(self.properties, "ui_expanded_document", text="",
+            icon=('TRIA_DOWN' if self.ui_expanded_document else 'TRIA_RIGHT'), emboss=False)
+        row.label(text="Document Settings")
+
+        if self.ui_expanded_document:
+            box.prop(self.properties, "file_format", text="Format")
+            box.prop(self.properties, "page_size_preset")
+            col = box.column(align=True)
+            col.active = self.page_size_preset == 'USER'
+            col.prop(self.properties, "output_size_x")
+            col.prop(self.properties, "output_size_y")
+            box.prop(self.properties, "output_margin")
+            col = box.column()
+            col.prop(self.properties, "do_create_stickers")
+            col.prop(self.properties, "do_create_numbers")
+            col = box.column()
+            col.active = self.do_create_stickers or self.do_create_numbers
+            col.prop(self.properties, "sticker_width")
+            box.prop(self.properties, "angle_epsilon")
+
+            box.prop(self.properties, "output_type")
+            col = box.column()
+            col.active = (self.output_type != 'NONE')
+            if len(self.object.data.uv_textures) == 8:
+                col.label(text="No UV slots left, No Texture is the only option.", icon='ERROR')
+            elif context.scene.render.engine not in ('BLENDER_RENDER', 'CYCLES') and self.output_type != 'NONE':
+                col.label(text="Blender Internal engine will be used for texture baking.", icon='ERROR')
+            col.prop(self.properties, "output_dpi")
+            row = col.row()
+            row.active = self.file_format == 'SVG'
+            row.prop(self.properties, "image_packing", text="Images")
+
+        box = layout.box()
+        row = box.row(align=True)
+        row.prop(self.properties, "ui_expanded_style", text="",
+            icon=('TRIA_DOWN' if self.ui_expanded_style else 'TRIA_RIGHT'), emboss=False)
+        row.label(text="Colors and Style")
+
+        if self.ui_expanded_style:
+            box.prop(self.style, "line_width", text="Default line width")
+            col = box.column()
+            col.prop(self.style, "outer_color")
+            col.prop(self.style, "outer_width", text="Relative width")
+            col.prop(self.style, "outer_style", text="Style")
+            col = box.column()
+            col.active = self.output_type != 'NONE'
+            col.prop(self.style, "use_outbg", text="Outer Lines Highlight:")
+            sub = col.column()
+            sub.active = self.output_type != 'NONE' and self.style.use_outbg
+            sub.prop(self.style, "outbg_color", text="")
+            sub.prop(self.style, "outbg_width", text="Relative width")
+            col = box.column()
+            col.prop(self.style, "convex_color")
+            col.prop(self.style, "convex_width", text="Relative width")
+            col.prop(self.style, "convex_style", text="Style")
+            col = box.column()
+            col.prop(self.style, "concave_color")
+            col.prop(self.style, "concave_width", text="Relative width")
+            col.prop(self.style, "concave_style", text="Style")
+            col = box.column()
+            col.prop(self.style, "freestyle_color")
+            col.prop(self.style, "freestyle_width", text="Relative width")
+            col.prop(self.style, "freestyle_style", text="Style")
+            col = box.column()
+            col.active = self.output_type != 'NONE'
+            col.prop(self.style, "use_inbg", text="Inner Lines Highlight:")
+            sub = col.column()
+            sub.active = self.output_type != 'NONE' and self.style.use_inbg
+            sub.prop(self.style, "inbg_color", text="")
+            sub.prop(self.style, "inbg_width", text="Relative width")
+            col = box.column()
+            col.active = self.do_create_stickers
+            col.prop(self.style, "sticker_fill")
+            box.prop(self.style, "text_color")
+
+
+def menu_func(self, context):
+    self.layout.operator("export_mesh.paper_model", text="Paper Model (.svg)")
+
+
+class VIEW3D_MT_paper_model_presets(bpy.types.Menu):
+    bl_label = "Paper Model Presets"
+    preset_subdir = "export_mesh"
+    preset_operator = "script.execute_preset"
+    draw = bpy.types.Menu.draw_preset
+
+
+class AddPresetPaperModel(bl_operators.presets.AddPresetBase, bpy.types.Operator):
+    """Add or remove a Paper Model Preset"""
+    bl_idname = "export_mesh.paper_model_preset_add"
+    bl_label = "Add Paper Model Preset"
+    preset_menu = "VIEW3D_MT_paper_model_presets"
+    preset_subdir = "export_mesh"
+    preset_defines = ["op = bpy.context.active_operator"]
+
+    @property
+    def preset_values(self):
+        op = bpy.ops.export_mesh.paper_model
+        properties = op.get_rna().bl_rna.properties.items()
+        blacklist = bpy.types.Operator.bl_rna.properties.keys()
+        return ["op.{}".format(prop_id) for (prop_id, prop) in properties
+            if not (prop.is_hidden or prop.is_skip_save or prop_id in blacklist)]
+
+
+class VIEW3D_PT_paper_model_tools(bpy.types.Panel):
+    bl_label = "Tools"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "TOOLS"
+    bl_category = "Paper Model"
+
+    def draw(self, context):
+        layout = self.layout
+        sce = context.scene
+        obj = context.active_object
+        mesh = obj.data if obj and obj.type == 'MESH' else None
+
+        layout.operator("export_mesh.paper_model")
+
+        col = layout.column(align=True)
+        col.label("Customization:")
+        col.operator("mesh.unfold")
+
+        if context.mode == 'EDIT_MESH':
+            row = layout.row(align=True)
+            row.operator("mesh.mark_seam", text="Mark Seam").clear = False
+            row.operator("mesh.mark_seam", text="Clear Seam").clear = True
+        else:
+            layout.operator("mesh.clear_all_seams")
+
+        layout.prop(sce.paper_model, "scale", text="Model Scale: 1")
+
+        col = layout.column(align=True)
+        col.prop(sce.paper_model, "limit_by_page")
+        sub = col.column(align=True)
+        sub.active = sce.paper_model.limit_by_page
+        sub.prop(sce.paper_model, "output_size_x")
+        sub.prop(sce.paper_model, "output_size_y")
+
+
+class VIEW3D_PT_paper_model_islands(bpy.types.Panel):
+    bl_label = "Islands"
+    bl_space_type = "VIEW_3D"
+    bl_region_type = "TOOLS"
+    bl_category = "Paper Model"
+
+    def draw(self, context):
+        layout = self.layout
+        sce = context.scene
+        obj = context.active_object
+        mesh = obj.data if obj and obj.type == 'MESH' else None
+
+        if mesh and mesh.paper_island_list:
+            layout.label(text="1 island:" if len(mesh.paper_island_list) == 1 else
+                "{} islands:".format(len(mesh.paper_island_list)))
+            layout.template_list('UI_UL_list', 'paper_model_island_list', mesh,
+                'paper_island_list', mesh, 'paper_island_index', rows=1, maxrows=5)
+            if mesh.paper_island_index >= 0:
+                list_item = mesh.paper_island_list[mesh.paper_island_index]
+                sub = layout.column(align=True)
+                sub.prop(list_item, "auto_label")
+                sub.prop(list_item, "label")
+                sub.prop(list_item, "auto_abbrev")
+                row = sub.row()
+                row.active = not list_item.auto_abbrev
+                row.prop(list_item, "abbreviation")
+        else:
+            layout.label(text="Not unfolded")
+            layout.box().label("Use the 'Unfold' tool")
+        sub = layout.column(align=True)
+        sub.active = bool(mesh and mesh.paper_island_list)
+        sub.prop(sce.paper_model, "display_islands", icon='RESTRICT_VIEW_OFF')
+        row = sub.row(align=True)
+        row.active = bool(sce.paper_model.display_islands and mesh and mesh.paper_island_list)
+        row.prop(sce.paper_model, "islands_alpha", slider=True)
+
+
+def display_islands(self, context):
+    # TODO: save the vertex positions and don't recalculate them always?
+    ob = context.active_object
+    if not ob or ob.type != 'MESH':
+        return
+    mesh = ob.data
+    if not mesh.paper_island_list or mesh.paper_island_index == -1:
+        return
+
+    bgl.glMatrixMode(bgl.GL_PROJECTION)
+    perspMatrix = context.space_data.region_3d.perspective_matrix
+    perspBuff = bgl.Buffer(bgl.GL_FLOAT, (4, 4), perspMatrix.transposed())
+    bgl.glLoadMatrixf(perspBuff)
+    bgl.glMatrixMode(bgl.GL_MODELVIEW)
+    objectBuff = bgl.Buffer(bgl.GL_FLOAT, (4, 4), ob.matrix_world.transposed())
+    bgl.glLoadMatrixf(objectBuff)
+    bgl.glEnable(bgl.GL_BLEND)
+    bgl.glBlendFunc(bgl.GL_SRC_ALPHA, bgl.GL_ONE_MINUS_SRC_ALPHA)
+    bgl.glEnable(bgl.GL_POLYGON_OFFSET_FILL)
+    bgl.glPolygonOffset(0, -10)  # offset in Zbuffer to remove flicker
+    bgl.glPolygonMode(bgl.GL_FRONT_AND_BACK, bgl.GL_FILL)
+    bgl.glColor4f(1.0, 0.4, 0.0, self.islands_alpha)
+    island = mesh.paper_island_list[mesh.paper_island_index]
+    for lface in island.faces:
+        face = mesh.polygons[lface.id]
+        bgl.glBegin(bgl.GL_POLYGON)
+        for vertex_id in face.vertices:
+            vertex = mesh.vertices[vertex_id]
+            bgl.glVertex4f(*vertex.co.to_4d())
+        bgl.glEnd()
+    bgl.glPolygonOffset(0.0, 0.0)
+    bgl.glDisable(bgl.GL_POLYGON_OFFSET_FILL)
+    bgl.glLoadIdentity()
+display_islands.handle = None
+
+
+def display_islands_changed(self, context):
+    """Switch highlighting islands on/off"""
+    if self.display_islands:
+        if not display_islands.handle:
+            display_islands.handle = bpy.types.SpaceView3D.draw_handler_add(display_islands, (self, context), 'WINDOW', 'POST_VIEW')
+    else:
+        if display_islands.handle:
+            bpy.types.SpaceView3D.draw_handler_remove(display_islands.handle, 'WINDOW')
+            display_islands.handle = None
+
+
+def label_changed(self, context):
+    """The label of an island was changed"""
+    # accessing properties via [..] to avoid a recursive call after the update
+    self["auto_label"] = not self.label or self.label.isspace()
+    island_item_changed(self, context)
+
+
+def island_item_changed(self, context):
+    """The labelling of an island was changed"""
+    # accessing properties via [..] to avoid a recursive call after the update
+    island_list = context.active_object.data.paper_island_list
+    if self.auto_label:
+        self["label"] = ""  # avoid self-conflict
+        number = 1
+        while any(item.label == "Island {}".format(number) for item in island_list):
+            number += 1
+        self["label"] = "Island {}".format(number)
+    if self.auto_abbrev:
+        self["abbreviation"] = "".join(first_letters(self.label))[:3].upper()
+    elif len(self.abbreviation) > 3:
+        self["abbreviation"] = self.abbreviation[:3]
+    self.name = "[{}] {} ({} {})".format(self.abbreviation, self.label, len(self.faces), "faces" if len(self.faces) > 1 else "face")
+
+
+class FaceList(bpy.types.PropertyGroup):
+    id = bpy.props.IntProperty(name="Face ID")
+
+
+class IslandList(bpy.types.PropertyGroup):
+    faces = bpy.props.CollectionProperty(type=FaceList, name="Faces",
+        description="Faces belonging to this island")
+    label = bpy.props.StringProperty(name="Label",
+        description="Label on this island",
+        default="", update=label_changed)
+    abbreviation = bpy.props.StringProperty(name="Abbreviation",
+        description="Three-letter label to use when there is not enough space",
+        default="", update=island_item_changed)
+    auto_label = bpy.props.BoolProperty(name="Auto Label",
+        description="Generate the label automatically",
+        default=True, update=island_item_changed)
+    auto_abbrev = bpy.props.BoolProperty(name="Auto Abbreviation",
+        description="Generate the abbreviation automatically",
+        default=True, update=island_item_changed)
+bpy.utils.register_class(FaceList)
+bpy.utils.register_class(IslandList)
+
+
+class PaperModelSettings(bpy.types.PropertyGroup):
+    display_islands = bpy.props.BoolProperty(name="Highlight selected island",
+        description="Highlight faces corresponding to the selected island in the 3D View",
+        options={'SKIP_SAVE'}, update=display_islands_changed)
+    islands_alpha = bpy.props.FloatProperty(name="Opacity",
+        description="Opacity of island highlighting", min=0.0, max=1.0, default=0.3)
+    limit_by_page = bpy.props.BoolProperty(name="Limit Island Size",
+        description="Do not create islands larger than given dimensions", default=False)
+    output_size_x = bpy.props.FloatProperty(name="Width",
+        description="Maximal width of an island",
+        default=0.2, soft_min=0.105, soft_max=0.841, subtype="UNSIGNED", unit="LENGTH")
+    output_size_y = bpy.props.FloatProperty(name="Height",
+        description="Maximal height of an island",
+        default=0.29, soft_min=0.148, soft_max=1.189, subtype="UNSIGNED", unit="LENGTH")
+    scale = bpy.props.FloatProperty(name="Scale",
+        description="Divisor of all dimensions when exporting",
+        default=1, soft_min=1.0, soft_max=10000.0, step=100, subtype='UNSIGNED', precision=1)
+bpy.utils.register_class(PaperModelSettings)
+
+
+def register():
+    bpy.utils.register_module(__name__)
+
+    bpy.types.Scene.paper_model = bpy.props.PointerProperty(type=PaperModelSettings,
+        name="Paper Model",
+        description="Settings of the Export Paper Model script",
+        options={'SKIP_SAVE'})
+    bpy.types.Mesh.paper_island_list = bpy.props.CollectionProperty(type=IslandList,
+        name="Island List", description="")
+    bpy.types.Mesh.paper_island_index = bpy.props.IntProperty(name="Island List Index",
+        default=-1, min=-1, max=100, options={'SKIP_SAVE'})
+    bpy.types.INFO_MT_file_export.append(menu_func)
+
+
+def unregister():
+    bpy.utils.unregister_module(__name__)
+    bpy.types.INFO_MT_file_export.remove(menu_func)
+    if display_islands.handle:
+        bpy.types.SpaceView3D.draw_handler_remove(display_islands.handle, 'WINDOW')
+        display_islands.handle = None
+
+if __name__ == "__main__":
+    register()