From 306be12bfad9de3c0fee353feaaa9904bc925fb6 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 3 May 2019 20:13:45 +0300
Subject: [PATCH] Major rework of mesh handling in Blender exporter

All of the preprocessing has been moved out of the MeshExporter class and
into a utility function.  This should make it easier for other exporter
classes to use meshes.
---
 blender/io_mspgl/export_mesh.py | 117 +--------
 blender/io_mspgl/mesh.py        | 416 +++++++++++++++++++++-----------
 2 files changed, 283 insertions(+), 250 deletions(-)

diff --git a/blender/io_mspgl/export_mesh.py b/blender/io_mspgl/export_mesh.py
index b695b40e..6d90c8fa 100644
--- a/blender/io_mspgl/export_mesh.py
+++ b/blender/io_mspgl/export_mesh.py
@@ -192,24 +192,7 @@ class MeshExporter:
 		if obj is None:
 			obj = context.active_object
 
-		objs = [(obj, mathutils.Matrix())]
-		check = objs
-		while check:
-			children = []
-			for o, m in check:
-				for c in o.children:
-					if c.compound:
-						children.append((c, m*c.matrix_local))
-			objs += children
-			check = children
-
-		if not objs:
-			raise Exception("Nothing to export")
-		for o, m in objs:
-			if o.type!="MESH":
-				raise Exception("Can only export Mesh data")
-
-		from .mesh import Mesh
+		from .mesh import create_mesh_from_object
 		from .util import Progress
 
 		if self.show_progress:
@@ -219,84 +202,7 @@ class MeshExporter:
 		else:
 			progress = None
 
-		mesh = None
-		bmeshes = []
-		winding_test = False
-		for o, m in objs:
-			if o.data.winding_test:
-				winding_test = True
-			if o.material_tex:
-				self.material_tex = True
-			bmesh = o.to_mesh(context.scene, True, "PREVIEW")
-			bmeshes.append(bmesh)
-			me = Mesh(bmesh)
-			me.transform(m)
-			if not mesh:
-				mesh = me
-			else:
-				mesh.splice(me)
-
-		if progress:
-			progress.set_task("Smoothing", 0.05, 0.35)
-		if mesh.smoothing=="NONE":
-			mesh.flatten_faces()
-		mesh.split_smooth(progress)
-
-		if mesh.smoothing!="BLENDER":
-			mesh.compute_normals()
-
-		if mesh.vertex_groups:
-			mesh.sort_vertex_groups(mesh.max_groups_per_vertex)
-
-			# Create a mapping from vertex group indices to bone indices
-			first_obj = objs[0][0]
-			group_index_map = dict((i, i) for i in range(len(first_obj.vertex_groups)))
-			if first_obj.parent and first_obj.parent.type=="ARMATURE":
-				armature = first_obj.parent.data
-				bone_indices = dict((armature.bones[i].name, i) for i in range(len(armature.bones)))
-				for g in first_obj.vertex_groups:
-					if g.name in bone_indices:
-						group_index_map[g.index] = bone_indices[g.name]
-
-		if self.material_tex and mesh.materials:
-			mesh.generate_material_uv()
-
-		texunits = []
-		force_unit0 = False
-		if mesh.uv_layers and (mesh.use_uv!="NONE" or self.material_tex):
-			# Figure out which UV layers to export
-			if mesh.use_uv=="ALL":
-				texunits = range(len(mesh.uv_layers))
-			elif self.material_tex:
-				# The material UV layer is always the last one
-				texunits = [len(mesh.uv_layers)-1]
-				force_unit0 = True
-			else:
-				for i, u in enumerate(mesh.uv_layers):
-					if u.unit==0:
-						texunits = [i]
-						break
-			texunits = [(i, mesh.uv_layers[i]) for i in texunits]
-			texunits = [u for u in texunits if not u[1].hidden]
-
-			if mesh.tbn_vecs:
-				# TBN coordinates must be generated before vertices are split by any other layer
-				uv_names = [u.name for i, u in texunits]
-				if mesh.tbn_uvtex in uv_names:
-					tbn_index = uv_names.index(mesh.tbn_uvtex)
-					unit = texunits[tbn_index]
-					del texunits[tbn_index]
-					texunits.insert(0, unit)
-
-			for i, u in texunits:
-				if progress:
-					progress.set_task("Splitting UVs", 0.35+0.3*i/len(texunits), 0.35+0.3*(i+1)/len(texunits))
-				mesh.split_uv(i, progress)
-				if mesh.tbn_vecs and u.name==mesh.tbn_uvtex:
-					mesh.compute_uv()
-					mesh.compute_tbn(i)
-
-			mesh.compute_uv()
+		mesh = create_mesh_from_object(context, obj, progress)
 
 		strips = []
 		loose = mesh.faces
@@ -312,10 +218,10 @@ class MeshExporter:
 		out_file = open_output(out_file)
 
 		fmt = ["NORMAL3"]
-		if texunits:
-			for i, u in texunits:
-				size = str(len(mesh.vertices[0].uvs[i]))
-				if u.unit==0 or force_unit0:
+		if mesh.uv_layers:
+			for u in mesh.uv_layers:
+				size = str(len(u.uvs[0]))
+				if u.unit==0:
 					fmt.append("TEXCOORD"+size)
 				else:
 					fmt.append("TEXCOORD%s_%d"%(size, u.unit))
@@ -334,10 +240,10 @@ class MeshExporter:
 			if v.normal!=normal:
 				out_file.write("normal3", *v.normal)
 				normal = v.normal
-			for i, u in texunits:
+			for i, u in enumerate(mesh.uv_layers):
 				if v.uvs[i]!=uvs.get(i):
 					size = str(len(v.uvs[i]))
-					if u.unit==0 or force_unit0:
+					if u.unit==0:
 						out_file.write("texcoord"+size, *v.uvs[i])
 					else:
 						out_file.write("multitexcoord"+size, u.unit, *v.uvs[i])
@@ -379,19 +285,16 @@ class MeshExporter:
 					out_file.write("indices", f.vertices[0].index, f.vertices[i-1].index, f.vertices[i].index)
 			out_file.end()
 
-		if mesh.use_lines and mesh.lines:
+		if mesh.lines:
 			out_file.begin("batch", "LINES")
 			for l in mesh.lines:
 				out_file.write("indices", l.vertices[0].index, l.vertices[1].index)
 			out_file.end()
 
-		if winding_test:
+		if mesh.winding_test:
 			out_file.write("winding", "COUNTERCLOCKWISE")
 
 		if progress:
 			progress.set_task("Done", 1.0, 1.0)
 
-		for m in bmeshes:
-			bpy.data.meshes.remove(m)
-
 		return mesh
diff --git a/blender/io_mspgl/mesh.py b/blender/io_mspgl/mesh.py
index d05b9de8..62d75063 100644
--- a/blender/io_mspgl/mesh.py
+++ b/blender/io_mspgl/mesh.py
@@ -1,3 +1,4 @@
+import bpy
 import math
 import mathutils
 
@@ -13,6 +14,7 @@ class Edge:
 		else:
 			self._medge = me
 			self.smooth = False
+		self.key = me.key
 		self.faces = []
 
 	def __getattr__(self, attr):
@@ -45,22 +47,21 @@ class Vertex:
 	def __init__(self, mv):
 		if mv.__class__==Vertex:
 			self._mvert = mv._mvert
-			self.co = mv.co
-			self.normal = mv.normal
 			self.uvs = mv.uvs[:]
 			self.tan = mv.tan
 			self.bino = mv.bino
-			self.group_weight_scale = mv.group_weight_scale
 		else:
 			self._mvert = mv
-			self.co = mv.co
-			self.normal = mv.normal
 			self.uvs = []
 			self.tan = None
 			self.bino = None
-			self.group_weight_scale = 1
+		self.index = mv.index
+		self.co = mv.co
+		self.normal = mv.normal
 		self.flag = False
+		self.edges = []
 		self.faces = []
+		self.groups = mv.groups[:]
 
 	def __getattr__(self, attr):
 		return getattr(self._mvert, attr)
@@ -71,9 +72,20 @@ class Vertex:
 		return cmp(self.index, other.index)
 
 
+class VertexGroup:
+	def __init__(self, base):
+		self._base = base
+		self.group = base.group
+		self.weight = base.weight
+
+	def __getattr__(self, attr):
+		return getattr(self._mvert, attr)
+
+
 class Face:
 	def __init__(self, mf):
 		self._mface = mf
+		self.index = mf.index
 		self.edges = []
 		self.vertices = mf.vertices[:]
 		self.uvs = []
@@ -101,6 +113,11 @@ class Face:
 				return e
 		raise KeyError("No edge %s"%(key,))
 
+	def other_edge(self, e, v):
+		for d in self.edges:
+			if d!=e and v in d.vertices:
+				return d
+
 	def get_neighbors(self):
 		neighbors = [e.other_face(self) for e in self.edges]
 		return list(filter(bool, neighbors))
@@ -114,12 +131,18 @@ class Line:
 
 
 class UvLayer:
-	def __init__(self, l, t):
-		self._layer = l
-		self.uvtex = t
-		self.name = self.uvtex.name
+	def __init__(self, arg):
+		if type(arg)==str:
+			self._layer = None
+			self.name = arg
+		else:
+			self._layer = arg
+			self.name = arg.name
+			self.uvs = [d.uv for d in self.data]
+
 		self.unit = None
 		self.hidden = False
+
 		dot = self.name.find('.')
 		if dot>=0:
 			ext = self.name[dot:]
@@ -131,60 +154,62 @@ class UvLayer:
 	def __getattr__(self, attr):
 		return getattr(self._layer, attr)
 
-class FakeUvLayer:
-	def __init__(self, n):
-		self.uvtex = None
-		self.name = n
-		self.unit = None
-		self.hidden = False
 
 class Mesh:
 	def __init__(self, m):
 		self._mesh = m
 
+		self.winding_test = m.winding_test
+		self.tbn_vecs = m.tbn_vecs
+		self.vertex_groups = m.vertex_groups
+
 		self.vertices = [Vertex(v) for v in self.vertices]
 		self.faces = [Face(f) for f in self.polygons]
+		self.edges = [Edge(e) for e in self.edges]
+		self.edge_map = {e.key: e for e in self.edges}
+		self.loops = self.loops[:]
 
 		self.materials = self.materials[:]
+		if self.use_uv=='NONE':
+			self.uv_layers = []
+		elif self.uv_layers:
+			self.uv_layers = [UvLayer(u) for u in self.uv_layers]
+			self.uv_layers = sorted([u for u in self.uv_layers if not u.hidden], key=(lambda u: (u.unit or 1000, u.name)))
+
+			if self.use_uv=='UNIT0':
+				self.uv_layers = [self.uv_layers[0]]
+
+			next_unit = max((u.unit+1 for u in self.uv_layers if u.unit is not None), default=0)
+			for u in self.uv_layers:
+				if not u.unit:
+					u.unit = next_unit
+					next_unit += 1
 
-		self.uv_layers = [UvLayer(self.uv_layers[i], self.uv_textures[i]) for i in range(len(self.uv_layers))]
-		self.assign_texture_units()
+		for v in self.vertices:
+			v.groups = [VertexGroup(g) for g in v.groups]
 
 		for f in self.faces:
 			if len(f.vertices)>4:
 				raise ValueError("Ngons are not supported")
+
 			f.vertices = [self.vertices[i] for i in f.vertices]
 			for v in f.vertices:
 				v.faces.append(f)
-			for u in self.uv_layers:
-				f.uvs.append([u.data[f.loop_indices[i]].uv for i in range(len(f.vertices))])
-			if f.material_index<len(self.materials):
-				mat = self.materials[f.material_index]
-				if mat and mat.array_atlas:
-					layer = (mat.array_layer,)
-					print(f.uvs, layer)
-					for i in range(len(f.uvs)):
-						f.uvs[i] = [mathutils.Vector(tuple(u)+layer) for u in f.uvs[i]]
-
-		self.edges = dict([(e.key, Edge(e)) for e in self.edges])
-		for f in self.faces:
+
 			for k in f.edge_keys:
-				e = self.edges[k]
-				e.faces.append(self.faces[f.index])
+				e = self.edge_map[k]
+				e.faces.append(f)
 				f.edges.append(e)
 
-		self.lines = [Line(e) for e in self.edges.values() if not e.faces]
-		for l in self.lines:
-			l.vertices = [self.vertices[i] for i in l.vertices]
+		for e in self.edges:
+			e.vertices = [self.vertices[i] for i in e.vertices]
+			for v in e.vertices:
+				v.edges.append(e)
 
-		if self.use_auto_smooth:
-			smooth_limit = math.cos(self.auto_smooth_angle)
+		if self.use_lines:
+			self.lines = [Line(e) for e in self.edges if not e.faces]
 		else:
-			smooth_limit = -1
-
-		for e in self.edges.values():
-			e.vertices = [self.vertices[i] for i in e.vertices]
-			e.check_smooth(smooth_limit)
+			self.lines = []
 
 	def __getattr__(self, attr):
 		return getattr(self._mesh, attr)
@@ -194,6 +219,12 @@ class Mesh:
 			v.co = matrix*v.co
 
 	def splice(self, other):
+		if len(self.uv_layers)!=len(other.uv_layers):
+			raise ValueError("Meshes have incompatible UV layers")
+		for i, u in enumerate(self.uv_layers):
+			if u.name!=other.uv_layers[i].name:
+				raise ValueError("Meshes have incompatible UV layers")
+
 		material_map = []
 		for m in other.materials:
 			if m in self.materials:
@@ -202,49 +233,128 @@ class Mesh:
 				material_map.append(len(self.materials))
 				self.materials.append(m)
 
+		for i, u in enumerate(self.uv_layers):
+			u.uvs += other.uv_layers[i].uvs
+
 		offset = len(self.vertices)
-		for v in other.vertices:
+		self.vertices += other.vertices
+		for v in self.vertices[offset:]:
 			v.index += offset
-			self.vertices.append(v)
+
+		loop_offset = len(self.loops)
+		self.loops += other.loops
 
 		offset = len(self.faces)
-		for f in other.faces:
+		self.faces += other.faces
+		for f in self.faces[offset:]:
 			f.index += offset
+			f.loop_start += loop_offset
+			f.loop_indices = range(f.loop_start, f.loop_start+f.loop_total)
 			if other.materials:
 				f.material_index = material_map[f.material_index]
-			self.faces.append(f)
 
-		for e in other.edges.values():
+		offset = len(self.edges)
+		self.edges += other.edges
+		for e in self.edges[offset:]:
+			e.index += offset
 			e.key = make_edge_key(e.vertices[0].index, e.vertices[1].index)
-			self.edges[e.key] = e
+			self.edge_map[e.key] = e
 
 		self.lines += other.lines
 
-	def flatten_faces(self):
-		for f in self.faces:
-			f.use_smooth = False
+	def prepare_smoothing(self, progress=None):
+		smooth_limit = -1
+		if self.smoothing=='NONE':
+			for f in self.faces:
+				f.use_smooth = False
 
-		for e in self.edges.values():
-			e.check_smooth(1)
+			smooth_limit = 1
+		elif self.use_auto_smooth:
+			smooth_limit = math.cos(self.auto_smooth_angle)
+
+		for e in self.edges:
+			e.check_smooth(smooth_limit)
+
+		self.split_vertices(self.find_smooth_group, progress)
+
+		if self.smoothing!='BLENDER':
+			self.compute_normals()
+
+	def prepare_vertex_groups(self, obj):
+		for v in self.vertices:
+			if v.groups:
+				weight_sum = sum(g.weight for g in v.groups)
+				v.groups = sorted(v.groups, key=(lambda g: g.weight), reverse=True)[:self.max_groups_per_vertex]
+				weight_scale = weight_sum/sum(g.weight for g in v.groups)
+				for g in v.groups:
+					g.weight *= weight_scale
+
+		if obj.parent and obj.parent.type=="ARMATURE":
+			armature = obj.parent.data
+			bone_indices = {b.name: i for i, b in enumerate(armature.bones)}
+			group_index_map = {i: i for i in range(len(obj.vertex_groups))}
+			for g in first_obj.vertex_groups:
+				if g.name in bone_indices:
+					group_index_map[g.index] = bone_indices[g.name]
+
+			for v in self.vertices:
+				for g in v.groups:
+					g.group = group_index_map[g.group]
+
+	def prepare_uv(self, obj, progress=None):
+		if obj.material_tex and self.use_uv!='NONE':
+			layer = UvLayer("material_tex")
+
+			if self.use_uv=='UNIT0':
+				self.uv_layers = [layer]
+				layer.unit = 0
+			else:
+				self.uv_layers.append(layer)
+				layer.unit = max((u.unit+1 for u in self.uv_layers if u.unit is not None), default=0)
+
+			layer.uvs = [None]*len(self.loops)
+			for f in self.faces:
+				uv = mathutils.Vector(((f.material_index+0.5)/len(self.materials), 0.5))
+				for i in f.loop_indices:
+					layer.uvs[i] = uv
+
+		array_uv_layers = [t.uv_layer for m in self.materials if m.array_atlas for t in m.texture_slots if t and t.texture_coords=='UV']
+		array_uv_layers = [u for u in self.uv_layers if u.name in array_uv_layers]
+
+		if array_uv_layers:
+			for f in self.faces:
+				layer = 0
+				if f.material_index<len(self.materials):
+					mat = self.materials[f.material_index]
+					if mat and mat.array_atlas:
+						layer = mat.array_layer
+
+				for l in array_uv_layers:
+					for i in f.loop_indices:
+						l.uvs[i] = mathutils.Vector((*l.uvs[i], layer))
 
-	def assign_texture_units(self):
-		# Assign texture units for any non-hidden UV layers that lack one
-		units = [u.unit for u in self.uv_layers if u.unit is not None]
-		if units:
-			free_unit = max(units)+1
-		else:
-			free_unit = 0
-		for u in self.uv_layers:
-			if u.unit is None:
-				if not u.hidden:
-					u.unit = free_unit
-					free_unit += 1
-
-	def generate_material_uv(self):
-		self.uv_layers.append(FakeUvLayer("material_tex"))
-		self.assign_texture_units()
 		for f in self.faces:
-			f.uvs.append([((f.material_index+0.5)/len(self.materials), 0.5)]*len(f.vertices))
+			for u in self.uv_layers:
+				f.uvs.append([u.uvs[i] for i in f.loop_indices])
+
+		tbn_layer_index = -1
+		if self.tbn_vecs:
+			uv_names = [u.name for u in self.uv_layers]
+			if self.tbn_uvtex in uv_names:
+				tbn_layer_index = uv_names.index(self.tbn_uvtex)
+				self.compute_tbn(tbn_layer_index)
+				self.split_vertices(self.find_uv_group, progress, tbn_layer_index)
+
+		for i in range(len(self.uv_layers)):
+			self.split_vertices(self.find_uv_group, progress, i)
+
+		for v in self.vertices:
+			if v.faces:
+				f = v.faces[0]
+				i = f.vertices.index(v)
+				v.uvs = [u[i] for u in f.uvs]
+			else:
+				v.uvs = [(0.0, 0.0)]*len(self.uv_layers)
 
 	def split_vertices(self, find_group_func, progress, *args):
 		groups = []
@@ -264,41 +374,38 @@ class Mesh:
 				progress.set_progress(i*0.5/len(self.vertices))
 
 		for i in range(len(self.vertices)):
-			if len(groups[i])==1:
-				continue
-
 			for g in groups[i][1:]:
 				v = Vertex(self.vertices[i])
 				v.index = len(self.vertices)
 				self.vertices.append(v)
 
 				v_edges = []
-				v_edge_keys = set()
-				for f in g:
-					for e in f.edges:
-						if e.key in v_edge_keys or self.vertices[i] not in e.vertices:
-							continue
-
-						e_faces_in_g = [c for c in e.faces if c in g]
+				for e in self.vertices[i].edges:
+					e_faces_in_g = [f for f in e.faces if f in g]
+					if e_faces_in_g:
 						boundary = len(e_faces_in_g)<len(e.faces)
 						v_edges.append((e, boundary, e_faces_in_g))
-						v_edge_keys.add(e.key)
 
 				for e, boundary, e_faces_in_g in v_edges:
 					if boundary:
 						ne = Edge(e)
-						for c in e_faces_in_g:
-							e.faces.remove(c)
-							c.edges[c.edges.index(e)] = ne
-							ne.faces.append(c)
+						ne.index = len(self.edges)
+						self.edges.append(ne)
+
+						for f in e_faces_in_g:
+							e.faces.remove(f)
+							f.edges[f.edges.index(e)] = ne
+							ne.faces.append(f)
 						e = ne
 					else:
-						del self.edges[e.key]
+						del self.edge_map[e.key]
+						self.vertices[i].edges.remove(e)
+						v.edges.append(e)
 
 					e.vertices[e.vertices.index(self.vertices[i])] = v
 
 					e.key = make_edge_key(e.vertices[0].index, e.vertices[1].index)
-					self.edges[e.key] = e
+					self.edge_map[e.key] = e
 
 				for f in g:
 					self.vertices[i].faces.remove(f)
@@ -308,89 +415,69 @@ class Mesh:
 			if progress:
 				progress.set_progress(0.5+i*0.5/len(self.vertices))
 
-	def split_smooth(self, progress=None):
-		self.split_vertices(self.find_smooth_group, progress)
-
-	def split_uv(self, index, progress=None):
-		self.split_vertices(self.find_uv_group, progress, index)
-
 	def find_smooth_group(self, vertex, face):
 		face.flag = True
-		queue = [face]
 
-		for f in queue:
-			for e in f.edges:
-				other = e.other_face(f)
-				if other not in vertex.faces:
-					continue
+		edges = [e for e in face.edges if vertex in e.vertices]
+
+		group = [face]
+		for e in edges:
+			f = face
+			while e.smooth:
+				f = e.other_face(f)
+				if not f or f.flag:
+					break
 
-				if e.smooth:
-					if not other.flag:
-						other.flag = True
-						queue.append(other)
+				f.flag = True
+				group.append(f)
+				e = f.other_edge(e, vertex)
 
-		return queue
+		return group
 
 	def find_uv_group(self, vertex, face, index):
 		uv = face.uvs[index][face.vertices.index(vertex)]
 		face.flag = True
+
 		group = [face]
 		for f in vertex.faces:
 			if not f.flag and f.uvs[index][f.vertices.index(vertex)]==uv:
 				f.flag = True
 				group.append(f)
+
 		return group
 
 	def compute_normals(self):
 		for v in self.vertices:
-			if v.faces:
-				v.normal = mathutils.Vector()
-				for f in v.faces:
-					fv = f.pivot_vertices(v)
-					edge1 = fv[1].co-fv[0].co
-					edge2 = fv[-1].co-fv[0].co
-					if edge1.length and edge2.length:
-						weight = 1
-						if len(f.get_edge(fv[0], fv[1]).faces)==1:
-							weight += 1
-						if len(f.get_edge(fv[0], fv[-1]).faces)==1:
-							weight += 1
-						v.normal += f.normal*edge1.angle(edge2)*weight
-				if v.normal.length:
-					v.normal.normalize()
-				else:
-					v.normal = mathutils.Vector((0, 0, 1))
-			else:
-				# XXX Should use edges to compute normal
-				v.normal = mathutils.Vector((0, 0, 1))
+			v.normal = mathutils.Vector()
+			for f in v.faces:
+				fv = f.pivot_vertices(v)
+				edge1 = fv[1].co-fv[0].co
+				edge2 = fv[-1].co-fv[0].co
+				if edge1.length and edge2.length:
+					v.normal += f.normal*edge1.angle(edge2)
 
-	def compute_uv(self):
-		for v in self.vertices:
-			if v.faces:
-				f = v.faces[0]
-				i = f.vertices.index(v)
-				v.uvs = [u[i] for u in f.uvs]
+			if v.normal.length:
+				v.normal.normalize()
 			else:
-				v.uvs = [(0.0, 0.0)]*len(self.uv_layers)
+				v.normal = mathutils.Vector((0, 0, 1))
 
 	def compute_tbn(self, index):
-		if not self.uv_layers:
-			return
+		layer_uvs = self.uv_layers[index].uvs
 
 		for v in self.vertices:
 			v.tan = mathutils.Vector()
 			v.bino = mathutils.Vector()
 			for f in v.faces:
-				fv = f.pivot_vertices(v)
-				uv0 = fv[0].uvs[index]
-				uv1 = fv[1].uvs[index]
-				uv2 = fv[-1].uvs[index]
+				vi = f.vertices.index(v)
+				uv0 = layer_uvs[f.loop_indices[vi]]
+				uv1 = layer_uvs[f.loop_indices[vi+1]]
+				uv2 = layer_uvs[f.loop_indices[vi-1]]
 				du1 = uv1[0]-uv0[0]
 				du2 = uv2[0]-uv0[0]
 				dv1 = uv1[1]-uv0[1]
 				dv2 = uv2[1]-uv0[1]
-				edge1 = fv[1].co-fv[0].co
-				edge2 = fv[-1].co-fv[0].co
+				edge1 = f.vertices[vi+1].co-f.vertices[vi].co
+				edge2 = f.vertices[vi-1].co-f.vertices[vi].co
 				div = (du1*dv2-du2*dv1)
 				if div:
 					mul = edge1.angle(edge2)/div
@@ -402,11 +489,18 @@ class Mesh:
 			if v.bino.length:
 				v.bino.normalize()
 
-	def sort_vertex_groups(self, max_groups):
+	def drop_references(self):
 		for v in self.vertices:
-			if v.groups:
-				v.groups = sorted(v.groups, key=(lambda g: g.weight), reverse=True)
-				v.group_weight_scale = 1.0/sum(g.weight for g in v.groups[:max_groups])
+			v._mvert = None
+			for g in v.groups:
+				g._base = None
+		for e in self.edges:
+			e._medge = None
+		for f in self.faces:
+			f._mface = None
+		for u in self.uv_layers:
+			u._layer = None
+		self._mesh = None
 
 	def create_strip(self, face, max_len):
 		# Find an edge with another unused face next to it
@@ -452,3 +546,39 @@ class Mesh:
 				break
 
 		return result
+
+def create_mesh_from_object(context, obj, progress=None):
+	if obj.type!="MESH":
+		raise Exception("Object is not a mesh")
+
+	objs = [(obj, mathutils.Matrix())]
+	i = 0
+	while i<len(objs):
+		o, m = objs[i]
+		i += 1
+		for c in o.children:
+			if c.type=="MESH" and c.compound:
+				objs.append((c, m*c.matrix_local))
+
+	mesh = None
+	bmeshes = []
+	for o, m in objs:
+		bmesh = o.to_mesh(context.scene, True, "PREVIEW")
+		bmeshes.append(bmesh)
+		me = Mesh(bmesh)
+		me.transform(m)
+
+		if mesh:
+			mesh.splice(me)
+		else:
+			mesh = me
+
+	mesh.prepare_smoothing(progress)
+	mesh.prepare_vertex_groups(obj)
+	mesh.prepare_uv(obj, progress)
+
+	mesh.drop_references()
+	for m in bmeshes:
+		bpy.data.meshes.remove(m)
+
+	return mesh
-- 
2.43.0