Source code for flipper.kernel.flatstructure

''' A module for representing a triangulation with a preferred flat structure.

Provides two classes: Vector2 and FlatStructure.
    An Vector2 is a vector in RR^2
    A FlatStructure is a triangulation with an assignment of vectors to each edge. '''

import flipper

class Vector2:
    ''' This represents a point in RR^2. '''
    
    # Warning: This needs to be updated if the interals of this class ever change.
    __slots__ = ['x', 'y']
    
    def __init__(self, x, y):
        self.x, self.y = x, y
    def __str__(self):
        return "(%s, %s)" % (self.x, self.y)
    def __repr__(self):
        return str(self)
    def __reduce__(self):
        # Having __slots__ means we need to pickle manually.
        return (self.__class__, (self.x, self.y))
    def __iter__(self):
        return iter([self.x, self.y])
    def __eq__(self, other):
        return self.x == other.x and self.y == other.y
    def __neg__(self):
        return Vector2(-self.x, -self.y)
    def __add__(self, other):
        return Vector2(self.x + other.x, self.y + other.y)
    def __sub__(self, other):
        return self + -other
    def __mul__(self, other):
        return Vector2(self.x * other, self.y * other)

class FlatStructure:
    ''' This represents a triangulation with a flat structure.
    
    It is specified by a triangulation together with a map taking each edge to a Vector2.
    These should satisfy some standard relations like ``sum(vector[edge] for edge in triangle) == 0``.
    '''
    def __init__(self, triangulation, edge_vectors):
        assert isinstance(triangulation, flipper.kernel.Triangulation)
        assert isinstance(edge_vectors, dict)
        assert all(edge in edge_vectors for edge in triangulation.edges)
        assert all(isinstance(edge_vectors[edge], Vector2) for edge in triangulation.edges)
        
        assert all(sum([edge_vectors[edge] for edge in triangle], Vector2(0, 0)) == Vector2(0, 0) for triangle in triangulation)
        
        self.triangulation = triangulation
        self.edge_vectors = edge_vectors
    def __str__(self):
        return '\n'.join('%s --> %s' % (edge, self.edge_vectors[edge]) for edge in sorted(self.triangulation.positive_edges, key=lambda e: e.index))
    def __repr__(self):
        return str(self)