def ordered_intersect(left_parabola, right_parabola):
''' return only one of the functions from intersect '''
# check degenerate cases
if left_parabola.get_focus() == Point.NEG_INF():
return lambda d: Point.NEG_INF()
if right_parabola.get_focus() == Point.INF():
return lambda d: Point.INF()
# do something normal
intersections = left_parabola.intersect(right_parabola)
# if a left parabola has focus above the right one, it will be wider
# and there are two intersection points to the right; we want
# the closer one
ind = 0 if left_parabola.get_focus().get_y(
) > right_parabola.get_focus().get_y() else 1
return intersections[ind]
def INF():
''' return pseudo parabola object all the way to the right '''
return Parabola(Point.INF())
def circle_handle(self, beachline, voronoi_edges, voronoi_vertices,
verbose):
''' handle a circle event by modifying the beachline and graph
remove the corresponding arc from the beachline
return list of new events
'''
# get current sweep line location
directrix = self.location.get_y() - self.radius
# print("CIRCLE EVENT HERE:")
# print(self)
# first check if this event actually occurs, i.e. parabolas do intersect here
if len(beachline.find_exact(self.location.get_x(), directrix)) <= 3:
if verbose:
print(self.location)
print(
"THIS EVENT DOES NOT OCCUR OR HAS ALREADY BEEN PROCESSED")
return [] # do nothing
# this line is for testing only
exact_find = beachline.find_exact(self.location.get_x(), directrix)
if len(exact_find) == 3:
print("ALREADY PROCESSED")
### maintain beachline ###
# remove and replace beachline objects above this site
nodes = beachline.delete(self.location.get_x(), directrix)
# if there are multiple intersections here, the only ones that
# survive are the leftmost and rightmost arcs
# nodes should take the form arc, breakpoint, arc, breakpoint, arc, etc.
# where the arcs in the middle have all degenerated
# get the list of foci associated with these beachline elements
foci = [
nodes[0].pointer[0]
] # determines the parabola for the left breakpoint of the first arc
for i in range(len(nodes) // 2): # nodes has odd length
breakpoint = nodes[2 * i +
1] # extract the breakpoints to get the foci
foci.append(breakpoint.pointer[0]) # add only the left parabolas
foci = foci + nodes[-1].pointer[
1:] # add rightmost parabola + determinator of its right breakpoint
# remember middle arcs all disappear, leaving only two arcs
left_arc = Arc(None, Parabola(foci[1]), Parabola(foci[0]),
Parabola(foci[-2]))
breakpoint = BreakPoint(None, Parabola(foci[1]), Parabola(foci[-2]))
right_arc = Arc(None, Parabola(foci[-2]), Parabola(foci[1]),
Parabola(foci[-1]))
beachline.insert(left_arc, directrix)
beachline.insert(breakpoint, directrix)
beachline.insert(right_arc, directrix)
### graph maintenance using voronoi_edges and voronoi_vertices ###
collisions = frozenset(foci[1:-1]) # all sites colliding here
# if len(collisions) != 3:
# print("voronoi vertex determined by")
# for point in collisions:
# print(point)
# print("current location")
# print(self.location)
# print("exact find")
# for node in exact_find:
# print(node._str__())
# print("Break points")
# for break_point in node.keyfunc(directrix):
# print(break_point)
# print("deleted nodes")
# for node in nodes:
# print(node._str__())
# print("beachline")
# print(beachline)
# raise StopIteration
# all arcs except the leftmost and rightmost disappear
for i in range(1, len(foci) - 2): # len(foci)-2 is the rightmost arc
edge = Edge(foci[i], foci[i + 1])
other = foci[i - 1] if i > 1 else foci[
-2] # some vertex for comparison
# foci[i], foci[i+1] are adjacent
if edge in voronoi_edges:
voronoi_edges[edge].add(self.location)
voronoi_vertices[edge].add(collisions)
elif foci[i] != foci[i + 1]:
voronoi_edges[edge] = {self.location}
voronoi_vertices[edge] = {collisions}
edge = Edge(foci[1], foci[-2])
if edge in voronoi_edges:
voronoi_edges[edge].add(self.location)
voronoi_vertices[edge].add(collisions)
elif foci[1] != foci[-2]:
voronoi_edges[edge] = {self.location}
voronoi_vertices[edge] = {collisions}
### event creation ###
# new adjacent arcs are foci[0], foci[1], foci[-2] and foci[1], foci[-2], foci[-1]
new_event_list = []
left_point_set = {foci[0], foci[1], foci[-2]}
right_point_set = {foci[1], foci[-2], foci[-1]}
if foci[0] != Point.NEG_INF() and len(left_point_set) == 3:
if not are_collinear(foci[0], foci[1], foci[-2]):
left_circle = compute_circumcenter(foci[0], foci[1], foci[-2])
left_radius = left_circle.distance(foci[1])
left_event = Event(left_circle, EventType.CIRCLE, left_radius)
if self < left_event:
new_event_list.append(left_event)
if foci[-1] != Point.INF() and len(right_point_set) == 3:
if not are_collinear(foci[1], foci[-2], foci[-1]):
right_circle = compute_circumcenter(foci[1], foci[-2],
foci[-1])
right_radius = right_circle.distance(foci[-2])
right_event = Event(right_circle, EventType.CIRCLE,
right_radius)
# print("CIRCLE EVENT CREATED %s" %(right_event,))
if self < right_event:
new_event_list.append(right_event)
return new_event_list
def site_handle(self, beachline, voronoi_edges, voronoi_vertices, verbose):
''' handle a site event by modifying the beachline and graph
add an arc to the beachline, possibly splitting arcs
return list of new events
'''
### beachline maintenance ###
# currently the sweep line goes through self.location
directrix = self.location.get_y()
parabola = Parabola(self.location) # new parabola with this focus
# remove and replace the beachline objects above this site
nodes = beachline.delete(self.location.get_x(), directrix)
if len(nodes
) == 0: # no objects yet, first insert; handle this by itself
# print("NO NODES FOUND")
arc = Arc(None, parabola, Parabola.NEG_INF(), Parabola.INF())
beachline.insert(arc, directrix)
return []
# nodes is nicely sorted from left to right, may contain 1 or 3 objects
foci = [
] # list of foci of parabolas from left to right (by parabola order)
# print("PRINTING NODES HERE")
# for node in nodes:
# print(node.pointer[1])
if len(nodes) == 3: # this site lies below a breakpoint
left_pointer = nodes[0].pointer
right_pointer = nodes[2].pointer
foci = left_pointer[:2] + [self.location] + right_pointer[1:]
elif len(nodes) == 1:
pointer = nodes[0].pointer # nodes[0] is a single arc
foci = pointer[0:2] + [self.location] + pointer[1:]
else:
# print("shouldn't get here!!!")
# print(self)
# for node in nodes:
# print(node._str__())
raise Exception("should not get here")
new_nodes = [
] # new arcs and breakpoints to be inserted; should be 3/2 unless two points have the same y coord
if self.location.get_y() == foci[1].get_y(
): # same y coordinates, parabolas will only have one intersection
# events are processed left to right, the rightmost arc will also have to change
far_left = Parabola(foci[0])
center_left = Parabola(foci[1]) # which is equal to foci[3]
center_right = Parabola(foci[2])
far_right = Parabola(foci[4])
arc1 = Arc(None, center_left, far_left, center_right)
breakpoint1 = BreakPoint(None, center_left, center_right)
arc2 = Arc(None, center_right, center_left, far_right)
breakpoint2 = BreakPoint(None, center_right, far_right)
new_nodes.append(arc1)
new_nodes.append(breakpoint1)
new_nodes.append(arc2)
new_nodes.append(breakpoint2)
# the arc of far_right has not been removed, but its left parabola needs to be changed
try:
far_right_arc = nodes[-1].successor().successor()
if verbose:
print("This is the far right arc")
print(far_right_arc)
# manually reset for far_right_arc
far_right_arc.pointer[0] = self.location
def f(directrix):
left_breakpoint = Parabola.ordered_intersect(
center_right, far_right)(directrix)
right_breakpoint = Parabola.ordered_intersect(
far_right,
Parabola(far_right_arc.pointer[-1]))(directrix)
return (left_breakpoint, right_breakpoint)
# reset keyfunc as well
far_right_arc.keyfunc = f
assert far_right_arc.pointer[1] == foci[4]
new_nodes.append(
None) # because iteration will not see the last item
except: # this point lies below the rightmost arc
if verbose:
print("beneath rightmost arc")
else: # non-degenerate case
for i in range(1, len(foci) - 1): # len(foci) should be 5
arc = Arc(None, Parabola(foci[i]), Parabola(foci[i - 1]),
Parabola(foci[i + 1]))
# print("New breakpoint added")
breakpoint = BreakPoint(None, Parabola(foci[i]),
Parabola(foci[i + 1]))
# print(breakpoint)
new_nodes.append(arc)
new_nodes.append(breakpoint)
# this gives an extra duplicated breakpoint at the end of the list
# NOTE: make sure to insert in left to right order to handle degeneracies
for i in range(len(new_nodes) - 1):
# print("Inserting")
# print(new_nodes[i])
beachline.insert(new_nodes[i], directrix)
# print("resulting beachline:")
# print(beachline)
# print("end beachline")
### graph maintenance using voronoi_edges ###
# first handle the common case
if foci[1] == foci[
3]: # site point breaks up a single arc, tracing new edge
assert foci[1] != foci[2]
voronoi_edges[Edge(foci[1], foci[2])] = set()
voronoi_vertices[Edge(foci[1], foci[2])] = set()
else: # site event coincides with circle event
circumcenter = compute_circumcenter(foci[1], foci[2], foci[3])
new_vertex = nodes[1].keyfunc(
directrix
)[0] # nodes[1] is a BreakPoint representing the collision point, coord is repeated
# print("ADDING EDGES AMONG:")
# print(foci[1], foci[2], foci[3])
collision = frozenset({foci[1], foci[2], foci[3]})
# handle each triangle edge separately
# edge between 1, 3
voronoi_edges[Edge(foci[1], foci[3])].add(new_vertex)
voronoi_vertices[Edge(foci[1], foci[3])].add(collision)
# edge between 1 and 2
voronoi_edges[Edge(foci[1], foci[2])] = {new_vertex}
voronoi_vertices[Edge(foci[1], foci[2])] = {collision}
# edge between 2 and 3
voronoi_edges[Edge(foci[2], foci[3])] = {new_vertex}
voronoi_vertices[Edge(foci[2], foci[3])] = {collision}
### compute new events ###
# the only potential circle events added by this vertex so far are
# ones in which the arcs to the left and right disappear
# circle event occurs when sweep line hits the bottom of the circle
# recall foci has length 5 and contains the 5 foci associated with
# the relevant parabolas here; degeneracy when this site event
# is also a circle event is handled by the site event
new_event_list = []
# print("FOCUS FOR EVENTS FROM SITE HERE")
# for focus in foci:
# print(focus)
# check for extreme cases
if foci[0] != Point.NEG_INF():
if not are_collinear(foci[0], foci[1], foci[2]):
# print("%s, %s, %s not collinear" %(foci[0], foci[1], foci[2]))
left_circle = compute_circumcenter(foci[0], foci[1], foci[2])
# left_circle is where the arc to the left of this site disappears
left_radius = foci[2].distance(left_circle)
left_event = Event(left_circle, EventType.CIRCLE, left_radius)
# only add if this event is new
# if not left_circle.get_y() - left_radius == directrix:
if self < left_event:
# print("CIRCLE EVENT CREATED %s" %(left_event))
new_event_list.append(left_event)
if foci[4] != Point.INF():
if not are_collinear(foci[2], foci[3], foci[4]):
# print("%s, %s, %s not collinear" %(foci[2], foci[3], foci[4]))
right_circle = compute_circumcenter(foci[2], foci[3], foci[4])
right_radius = foci[2].distance(right_circle)
right_event = Event(right_circle, EventType.CIRCLE,
right_radius)
# if not right_circle.get_y() - right_radius == directrix:
if self < right_event:
# print("CIRCLE EVENT CREATED %s" %(right_event,))
new_event_list.append(right_event)
# recall new_nodes has an extra breakpoint at the end
return new_event_list
