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#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# C++ version Copyright (c) 2006-2007 Erin Catto http://www.box2d.org
# Python version by Ken Lauer / sirkne at gmail dot com
#
# This software is provided 'as-is', without any express or implied
# warranty. In no event will the authors be held liable for any damages
# arising from the use of this software.
# Permission is granted to anyone to use this software for any purpose,
# including commercial applications, and to alter it and redistribute it
# freely, subject to the following restrictions:
# 1. The origin of this software must not be misrepresented; you must not
# claim that you wrote the original software. If you use this software
# in a product, an acknowledgment in the product documentation would be
# appreciated but is not required.
# 2. Altered source versions must be plainly marked as such, and must not be
# misrepresented as being the original software.
# 3. This notice may not be removed or altered from any source distribution.
from .framework import (Framework, Keys, main)
from Box2D import (b2EdgeShape, b2FixtureDef, b2PolygonShape, b2RopeJointDef)
# From the original C++ testbed example:
# "This test shows how a rope joint can be used to stabilize a chain of bodies
# with a heavy payload. Notice that the rope joint just prevents excessive
# stretching and has no other effect. By disabling the rope joint you can see
# that the Box2D solver has trouble supporting heavy bodies with light bodies.
# Try playing around with the densities, time step, and iterations to see how
# they affect stability. This test also shows how to use contact filtering.
# Filtering is configured so that the payload does not collide with the
# chain."
class Rope (Framework):
name = "Rope Joint Test"
description = "Press j to toggle the rope joint."
def __init__(self):
super(Rope, self).__init__()
# The ground
ground = self.world.CreateBody(
shapes=b2EdgeShape(vertices=[(-40, 0), (40, 0)]))
shape = b2PolygonShape(box=(0.5, 0.125))
fd = b2FixtureDef(
shape=shape,
friction=0.2,
density=20,
categoryBits=0x0001,
maskBits=(0xFFFF & ~0x0002),
)
N = 10
y = 15.0
prevBody = ground
for i in range(N):
if i < N - 1:
body = self.world.CreateDynamicBody(
position=(0.5 + i, y),
fixtures=fd,
)
else:
shape.box = (1.5, 1.5)
fd.density = 100
fd.categoryBits = 0x0002
body = self.world.CreateDynamicBody(
position=(i, y),
fixtures=fd,
angularDamping=0.4,
)
self.world.CreateRevoluteJoint(
bodyA=prevBody,
bodyB=body,
anchor=(i, y),
collideConnected=False,
)
prevBody = body
extraLength = 0.01
self.rd = rd = b2RopeJointDef(
bodyA=ground,
bodyB=body,
maxLength=N - 1.0 + extraLength,
localAnchorA=(0, y),
localAnchorB=(0, 0)
)
self.rope = self.world.CreateJoint(rd)
def Step(self, settings):
super(Rope, self).Step(settings)
if self.rope:
self.Print('Rope ON')
else:
self.Print('Rope OFF')
def Keyboard(self, key):
if key == Keys.K_j:
if self.rope:
self.world.DestroyJoint(self.rope)
self.rope = None
else:
self.rope = self.world.CreateJoint(self.rd)
if __name__ == "__main__":
main(Rope)
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