219 lines
6.2 KiB
Python
219 lines
6.2 KiB
Python
from __future__ import division
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import json
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'''
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http://en.wikipedia.org/wiki/Polygon_mesh
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Polygon meshes may be represented in a variety of ways, using different methods
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to store the vertex, edge and face data. These include:
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- Face-vertex
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- Winged-edge
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- Half-edge
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- Quad-edge
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- Corner-tables
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- Vertex-vertex
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- Face-vertex
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We have chosen to use a winged-edge style mesh for our purpopses.
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'''
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__all__ = [
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'Vertex',
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'PolygonMesh',
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]
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def cross(a, b):
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i = a.y * b.z - a.z * b.y
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j = a.z * b.x - a.x * b.z
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k = a.x * b.y - a.y * b.x
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return Vertex(i, j, k)
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def centroid(verts):
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xs = [v.x for v in verts]
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ys = [v.y for v in verts]
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zs = [v.z for v in verts]
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# average each vertex component
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x = sum(xs) / len(xs)
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y = sum(ys) / len(ys)
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z = sum(zs) / len(zs)
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return Vertex(x, y, z)
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class Vertex(list):
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'''
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A vertex is a position along with other information such as color, normal
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vector and texture coordinates.
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For the sake of our algorithms, we will only worry about the (x, y, z)
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float positions. Eventually we will also keep track of weights.
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'''
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def __init__(self, *args, **kwargs):
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""" The constructor supports the following formats:
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>>> Vertex([3, 1, 4])
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V[3, 1, 4]
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>>> Vertex(2, 7, 2)
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V[2, 7, 2]
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>>> Vertex()
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V[0, 0, 0]
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"""
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if len(args) == 0:
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a = [[0, 0, 0]]
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a.extend(args)
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super(Vertex, self).__init__(*a, **kwargs)
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elif len(args) == 1:
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if len(args[0]) != 3:
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raise TypeError("Only support 3D at the moment")
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super(Vertex, self).__init__(*args, **kwargs)
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elif len(args) == 3:
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super(Vertex, self).__init__(args, **kwargs)
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@property
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def x(self):
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return self[0]
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@property
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def y(self):
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return self[1]
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@property
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def z(self):
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return self[2]
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def __eq__(self, other):
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if(self.x == other.x and self.y == other.y and self.z == other.z):
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return True
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else:
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return False
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def __add__(self, other):
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# for now just assume type(other) = Vertex... bad, I know
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return Vertex(self.x + other.x, self.y + other.y, self.z + other.z)
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__iadd__ = __add__
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def __radd__(self, other):
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return other + self
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def __mul__(self, other):
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if isinstance(other, Vertex):
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return cross(self, other)
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elif isinstance(other, (float, int)):
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return Vertex(self.x * other, self.y * other, self.z * other)
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else:
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raise TypeError("{0} has an unexpected type: {1}".format(
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other, type(other)))
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def __rmul__(self, other):
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return self.__mul__(other)
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def __div__(self, other):
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# same assumption as __mult__
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return Vertex(self.x / other, self.y / other, self.z / other)
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__truediv__ = __div__
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def __neg__(self):
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return Vertex(-self.x, -self.y, -self.z)
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def __unicode__(self):
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return 'V{0}'.format([self.x, self.y, self.z])
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__str__ = __unicode__
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__repr__ = __unicode__
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class PolygonMesh(object):
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'''
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A polygon object is a collection of the following lists:
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- a list containing the 3-space vertex information
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- a list containing the edge indices ([0, 1] means first and second
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elements of the vertices list)
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- a list of the faces (indices of the vertices in a given face)
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- connectivity information (eventually will be calculated given the verts,
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edges, and faces)
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'''
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def __init__(self, vertices, faces, edges=None, **kwargs):
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self.vertices = [Vertex(*v) for v in vertices]
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self.faces = faces
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self.edges = edges
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# the strategy for the following members involves lazy-instantiating
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# them if they weren't passing them in:
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self._faces_for_edge = kwargs.get('faces for edge', None)
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self._edges_for_face = kwargs.get('edges for face', None)
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self._edges_for_vert = kwargs.get('edges for vert', None)
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self._faces_for_vert = kwargs.get('faces for vert', None)
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@property
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def faces_for_edge(self):
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"""returns a list of face indices for a given edge index.
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Intended to be used in the following way:
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>>> # vs, es, fs, ffe, eff, efv, ffv from blender or similar
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>>> mesh = Polygon(vs, es, fs, ffe, eff, efv, ffv)
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>>> mesh.faces_for_edge[0]
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[0, 1]
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>>> [self.face[i] for i in mesh.faces_for_edge[1]]
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[[...], [...], ...]
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where 0 and 1 are indices into the face list
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"""
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if self._faces_for_edge is None:
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# TODO: eventually support generating this ourselves ...
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raise NotImplementedError
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return self._faces_for_edge
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@property
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def edges_for_face(self):
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"""returns a list of edge indices for a given face index."""
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# XXX
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if self._edges_for_face is None:
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self._edges_for_face = [[] for i in range(len(self.faces))]
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return self._edges_for_face
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@property
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def edges_for_vert(self):
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"""returns a list of edge indices for a given vertex index."""
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if self._edges_for_vert is None:
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self._edges_for_vert = [[] for i in range(len(self.vertices))]
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for i, edge in enumerate(self.edges):
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for vid in edge:
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self._edges_for_vert[vid].append(i)
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return self._edges_for_vert
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@property
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def faces_for_vert(self):
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"""returns a list of face indices for a given vert index."""
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if self._faces_for_vert is None:
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self._faces_for_vert = [[] for i in range(len(self.vertices))]
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for i, face in enumerate(self.faces):
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for vid in face:
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self._faces_for_vert[vid].append(i)
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return self._faces_for_vert
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def __unicode__(self):
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# TODO: perhaps also add connectivity here?
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d = {
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'vertices': self.vertices,
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'edges': self.edges,
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'faces': self.faces,
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}
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return json.dumps(d)
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__str__ = __unicode__
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__repr__ = __unicode__
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def centroid(self, vert_ids):
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verts = [self.vertices[vid] for vid in vert_ids]
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return centroid(verts)
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