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#!/usr/bin/python
#
# C++ version Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
# Python version Copyright (c) 2008 kne / sirkne at gmail dot com
#
# Implemented using the pybox2d SWIG interface for Box2D (pybox2d.googlecode.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 test_main import *
def calculate_bezier(p, steps = 30):
"""
Calculate a bezier curve from 4 control points and return a
list of the resulting points.
The function uses the forward differencing algorithm described here:
http://www.niksula.cs.hut.fi/~hkankaan/Homepages/bezierfast.html
"""
t = 1.0 / steps
temp = t*t
f = p[0]
fd = 3 * (p[1] - p[0]) * t
fdd_per_2 = 3 * (p[0] - 2 * p[1] + p[2]) * temp
fddd_per_2 = 3 * (3 * (p[1] - p[2]) + p[3] - p[0]) * temp * t
fddd = fddd_per_2 + fddd_per_2
fdd = fdd_per_2 + fdd_per_2
fddd_per_6 = fddd_per_2 * (1.0 / 3)
points = []
for x in range(steps):
points.append(f)
f = f + fd + fdd_per_2 + fddd_per_6
fd = fd + fdd + fddd_per_2
fdd = fdd + fddd
fdd_per_2 = fdd_per_2 + fddd_per_2
points.append(f)
return points
class BezierEdges (Framework):
name="BezierEdges"
control_points = [ ]
bezier_obj = []
selected_point = 0
_pickle_vars=['control_points', 'bezier_obj', 'selected_point']
def __init__(self):
super(BezierEdges, self).__init__()
self.control_points = [ box2d.b2Vec2(*t) for t in
[(0,0), (0,1), (0, 2), (0, 3)]]
# ground edge
verts = [ (50.0,0.0), (-50.0,0.0) ]
edgeDef = box2d.b2EdgeChainDef()
edgeDef.setVertices_tuple(verts)
edgeDef.isALoop = False
bd=box2d.b2BodyDef()
bd.position = ( 0.0, 0.0 )
ground = self.world.CreateBody(bd)
ground.CreateShape(edgeDef)
# some objects to use on the curve
sd=box2d.b2CircleDef()
sd.radius = 1.0
sd.density = 1.0
for i in xrange(4):
bd=box2d.b2BodyDef()
bd.position = (0.0, 2.0 + 3.0 * i)
body = self.world.CreateBody(bd)
body.CreateShape(sd)
body.SetMassFromShapes()
def Keyboard(self, key):
if key==K_c:
# create a new curve
bezier_verts = calculate_bezier(self.control_points)
ed = box2d.b2EdgeChainDef()
ed.setVertices_b2Vec2(bezier_verts)
ed.isALoop = False
bd=box2d.b2BodyDef()
bd.position = ( 0.0, 0.0 )
body = self.world.CreateBody(bd)
body.CreateShape(ed)
self.bezier_obj.append(body)
elif key==K_d:
# delete the most recent curve
if self.bezier_obj:
body = self.bezier_obj.pop()
self.world.DestroyBody( body )
elif key in (K_1, K_2, K_3, K_4):
self.selected_point = key-K_1
def ShiftMouseDown(self, p):
self.control_points[self.selected_point]=p
self.selected_point += 1
if self.selected_point > 3:
self.selected_point = 0
def Step(self, settings):
super(BezierEdges, self).Step(settings)
for p in self.control_points:
self.debugDraw.DrawCircle(p, 0.25, box2d.b2Color(1.0,0.0,0))
if __name__=="__main__":
main(BezierEdges)
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