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# MetroWind/naive-edge-offset.py

Last active December 13, 2021 07:49
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Offset a loop of edges. Probably only works in the simple case where the loop is convex and the internal ordering of the vertices is "nice".
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 # Offset a loop of edges. Probably only works in the simple case where the loop # is convex and the internal ordering of the vertices is "nice". # # Usage: # # 1. In edit mode, select a loop of vertices. The vertices should be roughly on # the same plane. # 2. Scroll to the bottom of this file, and change the offset distance in the # offset function call. The distance can be negative. # 3. Press "Run Script". import typing from typing import Set from collections.abc import Collection import bpy import bmesh import mathutils def normalVec(v0: mathutils.Vector, v1: mathutils.Vector, v2: mathutils.Vector) -> mathutils.Vector: """Return the normal vector of the plane formed by three points v0, v1, and v2. The ordering is v1 -> v0 -> v2.""" return (v1 - v0).cross(v0 - v2).normalized() class Queue(object): def __init__(self): self.data = [] def enqueue(self, x): self.data.append(x) def dequeue(self): del self.data[0] def head(self): return self.data[0] def empty(self): return len(self.data) == 0 def __contains__(self, x): return x in self.data class Offsetter(object): def __init__(self): self.object = bpy.context.selected_objects[0] self.bm = bmesh.new() self.bm.from_mesh(self.object.data) def getSelectedVertices(self) -> Set[bmesh.types.BMVert]: return set(v for v in self.bm.verts if v.select) @staticmethod def getNeighbors(v: bmesh.types.BMVert) -> Set[bmesh.types.BMVert]: """Return all vertices that share edge with vertex `v`.""" return set(edge.other_vert(v) for edge in v.link_edges) @staticmethod def offsetDir(v: mathutils.Vector, neighbor1: mathutils.Vector, neighbor2: mathutils.Vector, center: mathutils.Vector) -> mathutils.Vector: normal1 = normalVec(neighbor1, v, center) offset_dir1 = (neighbor1 - v).cross(normal1).normalized() normal2 = normalVec(neighbor2, v, center) offset_dir2 = (neighbor2 - v).cross(normal2).normalized() return ((offset_dir1 + offset_dir2) * 0.5).normalized() def selectVertices(self, vs: Collection[bmesh.types.BMVert]): self.bm.select_mode = {"VERT",} for v in vs: v.select_set(True) def offset(self, distance): verts = self.getSelectedVertices() print("Selected {} vertices".format(len(verts))) center = sum((v.co for v in verts), start=mathutils.Vector((0.0, 0.0, 0.0))) / len(verts) verts_to_go = Queue() verts_to_go.enqueue(next(iter(verts))) relation = dict() count = 0 while not verts_to_go.empty(): vert = verts_to_go.head() neighbors = tuple(v for v in self.getNeighbors(vert) if v in verts) if len(neighbors) != 2: raise RuntimeError("Selection is not a loop") # Calculate an offset direction from the two neighbors. This part # may be sensitive to the internal ordering of vertices in Blender. # Suppose we have 4 vertices connected like v0--v1--v2--v3. When # finding the normal vector of the plane on v1, we may use # v0--v1--v2, in this order. But when finding the normal vector on # v2, the ordering may be v3--v2--v1, and the resulting normal will # be oppsite to the previous normal. This can be fixed if we order # the 2 neighbors correctly in relation to the center coordinate. # And it's not a difficult fix. But we are not doing that here. direction = self.offsetDir(vert.co, neighbors[0].co, neighbors[1].co, center) new_vert = self.bm.verts.new(vert.co + direction * distance) count += 1 self.bm.edges.new((vert, new_vert)) relation[vert] = new_vert for neighbor in neighbors: if neighbor in relation: self.bm.edges.new((relation[neighbor], new_vert)) self.bm.faces.new((vert, neighbor, relation[neighbor], new_vert)) # If this is just an "else", the last vertex would be offset # twice for some reason. elif neighbor not in verts_to_go: verts_to_go.enqueue(neighbor) verts_to_go.dequeue() print("Created {} vertices.".format(count)) for v in verts: v.select_set(False) self.selectVertices(relation.values()) self.bm.to_mesh(self.object.data) # See https://stackoverflow.com/questions/15429796/blender-scripting-indices-of-selected-vertices bpy.ops.object.mode_set(mode='OBJECT') o = Offsetter() o.offset(-0.07) bpy.ops.object.mode_set(mode='EDIT')
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