surfaces/surf/geometry.py

from __future__ import division
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, polygon, x=0, y=0, z=0):
        self.polygon = polygon
        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__
        return Vertex(self.x / other, self.y / other, self.z / other)
    __truediv__ = __div__

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

class Edge(object):
    '''
    '''
    
    def __init__(self, polygon):
        self.polygon = polygon
        self.vertices = []
        self.faces = []
        self.edges = []
        
    def neighborFace(self, neighborFace):
        '''Get neighboring face id
        '''
        if neighborFace == self.faces[0]:
            return self.faces[1]
        else:
            return self.faces[0]

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, polygon):
        self.polygon = polygon
        self.edges = []
        
class Polygon(object):
    '''
    '''

    def __init__(self, vs=None, es=None, fs=None):
        self.vertices = vs or []
        self.edges = es or []
        self.faces = fs or []
    
    def __unicode__(self):
        d = {
            'vertices': self.vertices,
            'edges': self.edges,
            'faces': self.faces,
        }
        return pprint.pformat(d)
    
    __str__ = __unicode__
    __repr__ = __unicode__