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# simu  Robot simulation. {{{
#
# Copyright (C) 2009 Nicolas Schodet
#
# APBTeam:
# Web: http://apbteam.org/
# Email: team AT apbteam DOT org
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place  Suite 330, Boston, MA 021111307, USA.
#
# }}}
"""Obstacle with a round shape."""
from math import pi, cos, sin, sqrt
class RoundObstacle:
def __init__ (self, radius, level = 0):
self.pos = None
self.radius = radius
self.level = level
def intersect (self, a, b):
"""If the segment [AB] intersects the obstacle, return distance from a
to intersection point, else, return None."""
ab = sqrt ((b[0]  a[0]) ** 2 + (b[1]  a[1]) ** 2) # distance AB.
n = ((b[0]  a[0]) / ab, (b[1]  a[1]) / ab) # vector of length 1.
o = self.pos # obstacle center.
# To check if the line (AB) intersects the circle, compute distance
# from circle center to line using a dot product.
vao = (o[0]  a[0], o[1]  a[1]) # vector AO.
# dot product, (n[1], n[0]) is perpendicular to n.
doc = abs (vao[0] * n[1] + vao[1] * n[0])
if doc < self.radius:
# Line intersects, check if segment intersects.
m = vao[0] * n[0] + vao[1] * n[1]
f = sqrt (self.radius ** 2  doc ** 2)
if m  f > 0 and m  f < ab:
return m  f
elif m + f > 0 and m + f < ab:
return m + f
return None
