surfaces/surf/geometry.py

import pprint

'''
http://en.wikipedia.org/wiki/Polygon_mesh

Polygon meshes may be represented in a variety of ways, using different methods
to store the vertex, edge and face data. These include:
  - Face-vertex
  - Winged-edge
  - Half-edge
  - Quad-edge
  - Corner-tables
  - Vertex-vertex
  - Face-vertex

We have chosen to use a winged-edge style mesh for our purpopses.

'''

def cross(a, b):
    i = a.y * b.z - a.z * b.y
    j = a.z * b.x - a.x * b.z
    k = a.x * b.y - a.y * b.x
    return Vertex(i, j, k)


class Vertex(object):
    '''
    A vertex is a position along with other information such as color, normal
    vector and texture coordinates.
    '''
    def __init__(self, x=0, y=0, z=0):
        self.x = x
        self.y = y
        self.z = z
        self.edges = []

    def __eq__(self, other):
        if(self.x == other.x and self.y == other.y and self.z == other.z):
            return True
        else:
            return False

    def __repr__(self):
        return "[%.2f, %.2f, %.2f]" % (self.x, self.y, self.z)

    def __add__(self, other):
        # for now just assume type(other) = Vertex... bad, I know
        return Vertex(self.x + other.x, self.y + other.y, self.z + other.z)

    def __radd__(self, other):
        return other + self
        # return self.__add__(other)

    def __mul__(self, other):
        if isinstance(other, Vertex):
            return cross(self, other)
        elif isinstance(other, (float, int)):
            return Vertex(self.x * other, self.y * other, self.z * other)
        else:
            raise TypeError("{0} has an unexpected type: {1}".format(
                other, type(other)))

    def __rmul__(self, other):
        return self.__mul__(other)

    def __div__(self, other):
        # same assumption as __mult__
        other = float(other)
        return Vertex(self.x / other, self.y / other, self.z / other)

    def __neg__(self):
        return Vertex(-self.x, -self.y, -self.z)


class Edge(object):
    '''
    '''
    def __init__(self):
        self.vertices = []
        self.faces = []
        self.edges = []
        self.__edge_vertex = None
        self.__sub_edges = []

    def neighborFace(self, neighborFace):
        if neighborFace == self.faces[0]:
            return self.faces[1]
        else:
            return self.faces[0]

    @property
    def mid_point(self):
        return sum(self.vertices, Vertex()) / len(self.vertices)

    @property
    def sub_edges(self):
        if not self.__sub_edges:
            self.__sub_edges = [Edge(), Edge()]
            self.__sub_edges[0].vertices = [self.vertices[0], self.edge_vertex]
            self.__sub_edges[1].vertices = [self.edge_vertex, self.vertices[1]]
        return self.__sub_edges

    @property
    def edge_vertex(self):
        '''
        Set each edge vertices to be the average of the two neighboring
            face vertices and its two original end vertices.
        '''
        if not self.__edge_vertex:
            # two neighboring face vertices:
            neighboringFaceVertices = [face.centroid for face in self.faces]
            neighboringFaceVertices.extend(self.vertices)
            xs = [vertex.x for vertex in neighboringFaceVertices]
            ys = [vertex.y for vertex in neighboringFaceVertices]
            zs = [vertex.z for vertex in neighboringFaceVertices]
            x = sum(xs) / len(xs)
            y = sum(ys) / len(ys)
            z = sum(zs) / len(zs)
            self.__edge_vertex = Vertex(x, y, z)
            self.__edge_vertex.edges.extend(self.__sub_edges)
        return self.__edge_vertex

    def __averageVertices(self, vertices):
        return


class Face(object):
    '''
    A face is a closed set of edges, in which a triangle face has three edges,
    and a quad face has four edges.
    '''
    def __init__(self):
        self.edges = []
        self.__centroid = None
        self.__interior_edges = []
        self.__sub_faces = []

    @property
    def centroid(self):
        if not self.__centroid:
            # gather all face vertex coords
            face_vertices = list(set([vertex
                for edge in self.edges for vertex in edge.vertices]))
            xs = [vertex.x for vertex in face_vertices]
            ys = [vertex.y for vertex in face_vertices]
            zs = [vertex.z for vertex in face_vertices]

            # average each vertex component
            x = sum(xs) / len(xs)
            y = sum(ys) / len(ys)
            z = sum(zs) / len(zs)

            self.__centroid = Vertex(x, y, z)
        return self.__centroid

    @property
    def sub_faces(self):
        self.__setupSubDivisions()
        return self.__sub_faces

    @property
    def interior_edges(self):
        self.__setupSubDivisions()
        return self.__interior_edges

    def __setupSubDivisions(self):
        '''
           v0      ev0    v1
            *------e0-----*
            |      |      |
            |      |      |
       ev3 e|11----f5----e|1 ev1
            |      |      |
            |      |      |
            *------e2-----*
           v3      ev2    v2
        '''
        if not self.__sub_faces:
            # create empty sub_faces that will be filled with edge references
            # below
            #   these need to at least exist so the interior edges have
            # something to reference
            self.__sub_faces = [Face() for edge in self.edges]

        if not self.__interior_edges:
            # set up empty edge objects to be filled below
            self.__interior_edges = [Edge() for edge in self.edges]

            # each interior edge connects the exterior edge vertex (mid-point)
            # to the faceVertex (centroid)
            for index in range(len(self.edges)):
                prevIndex = (index - 1) % len(self.edges)
                nextIndex = (index + 1) % len(self.edges)

                # end vertices are face centroid and currEdge edge_vertex
                self.__interior_edges[index].vertices = [
                    self.edges[index].edge_vertex, self.centroid
                ]

                # wing edges are the current edge's sub_edges (ordered same as
                # vertex order) and the prev and next interior edges
                self.__interior_edges[index].edges = [
                    self.edges[index].sub_edges[0],
                    self.edges[index].sub_edges[1],
                    self.__interior_edges[prevIndex],
                    self.__interior_edges[nextIndex]
                ]

                # edge faces are the new sub_faces (current and next faces), the
                # current will be define below
                #   and the next will be defined on the next iteration (or
                # already defined on the last iteration)
                self.__interior_edges[index].faces = [
                    self.__sub_faces[index],
                    self.__sub_faces[nextIndex]
                ]

                # now reference the current edge back into the faces,
                #   and the edge.sub_edges, and the edge.edge_vertex

                # current subFace (same index as current interior edge)
                #   set its edges to reference the same edges used to setup the
                #      interior edge
                #   order will be pretty important on these steps...
                self.__sub_faces[index].edges = [
                    self.edges[index].sub_edges[0],
                    self.__interior_edges[index],
                    self.__interior_edges[prevIndex],
                    self.edges[prevIndex].sub_edges[1]
                ]

                # just set one of the vertex edges, the other belongs to
                # another face and will get added when that face is run
                self.edges[index].edge_vertex.edges.append(
                        self.__interior_edges[index])

                self.edges[index].sub_edges[0].faces.append(
                        self.__sub_faces[index])
                self.edges[index].sub_edges[0].faces.append(
                        self.__sub_faces[index])


class Polygon(object):
    '''
    Face splitting should happend on the polygon level(?).  It doesn't make
    sense to split just one face since it needs to average vertices with all
    adjoinging faces
    '''

    def __init__(self, v=None, e=None, f=None):
        self.vertices = v or []
        self.edges = e or []
        self.faces = f or []

    def __unicode__(self):
        d = {
            'vertices': self.vertices,
            'edges': self.edges,
            'faces': self.faces,
        }
        return pprint.pformat(d)

    __str__ = __unicode__
    __repr__ = __unicode__