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#!/usr/bin/env python
'''
Copyright (C) 2010 Nick Drobchenko, nick@cnc-club.ru
Copyright (C) 2005 Aaron Spike, aaron@ekips.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 02111-1307 USA
'''
import math, cmath
def rootWrapper(a,b,c,d):
if a:
# Monics formula see http://en.wikipedia.org/wiki/Cubic_function#Monic_formula_of_roots
a,b,c = (b/a, c/a, d/a)
m = 2.0*a**3 - 9.0*a*b + 27.0*c
k = a**2 - 3.0*b
n = m**2 - 4.0*k**3
w1 = -.5 + .5*cmath.sqrt(-3.0)
w2 = -.5 - .5*cmath.sqrt(-3.0)
if n < 0:
m1 = pow(complex((m+cmath.sqrt(n))/2),1./3)
n1 = pow(complex((m-cmath.sqrt(n))/2),1./3)
else:
if m+math.sqrt(n) < 0:
m1 = -pow(-(m+math.sqrt(n))/2,1./3)
else:
m1 = pow((m+math.sqrt(n))/2,1./3)
if m-math.sqrt(n) < 0:
n1 = -pow(-(m-math.sqrt(n))/2,1./3)
else:
n1 = pow((m-math.sqrt(n))/2,1./3)
x1 = -1./3 * (a + m1 + n1)
x2 = -1./3 * (a + w1*m1 + w2*n1)
x3 = -1./3 * (a + w2*m1 + w1*n1)
return (x1,x2,x3)
elif b:
det=c**2.0-4.0*b*d
if det:
return (-c+cmath.sqrt(det))/(2.0*b),(-c-cmath.sqrt(det))/(2.0*b)
else:
return -c/(2.0*b),
elif c:
return 1.0*(-d/c),
return ()
def bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3))):
#parametric bezier
x0=bx0
y0=by0
cx=3*(bx1-x0)
bx=3*(bx2-bx1)-cx
ax=bx3-x0-cx-bx
cy=3*(by1-y0)
by=3*(by2-by1)-cy
ay=by3-y0-cy-by
return ax,ay,bx,by,cx,cy,x0,y0
#ax,ay,bx,by,cx,cy,x0,y0=bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)))
def linebezierintersect(((lx1,ly1),(lx2,ly2)),((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3))):
#parametric line
dd=lx1
cc=lx2-lx1
bb=ly1
aa=ly2-ly1
if aa:
coef1=cc/aa
coef2=1
else:
coef1=1
coef2=aa/cc
ax,ay,bx,by,cx,cy,x0,y0=bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)))
#cubic intersection coefficients
a=coef1*ay-coef2*ax
b=coef1*by-coef2*bx
c=coef1*cy-coef2*cx
d=coef1*(y0-bb)-coef2*(x0-dd)
roots = rootWrapper(a,b,c,d)
retval = []
for i in roots:
if type(i) is complex and i.imag==0:
i = i.real
if type(i) is not complex and 0<=i<=1:
retval.append(bezierpointatt(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)),i))
return retval
def bezierpointatt(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)),t):
ax,ay,bx,by,cx,cy,x0,y0=bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)))
x=ax*(t**3)+bx*(t**2)+cx*t+x0
y=ay*(t**3)+by*(t**2)+cy*t+y0
return x,y
def bezierslopeatt(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)),t):
ax,ay,bx,by,cx,cy,x0,y0=bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)))
dx=3*ax*(t**2)+2*bx*t+cx
dy=3*ay*(t**2)+2*by*t+cy
return dx,dy
def beziertatslope(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)),(dy,dx)):
ax,ay,bx,by,cx,cy,x0,y0=bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)))
#quadratic coefficents of slope formula
if dx:
slope = 1.0*(dy/dx)
a=3*ay-3*ax*slope
b=2*by-2*bx*slope
c=cy-cx*slope
elif dy:
slope = 1.0*(dx/dy)
a=3*ax-3*ay*slope
b=2*bx-2*by*slope
c=cx-cy*slope
else:
return []
roots = rootWrapper(0,a,b,c)
retval = []
for i in roots:
if type(i) is complex and i.imag==0:
i = i.real
if type(i) is not complex and 0<=i<=1:
retval.append(i)
return retval
def tpoint((x1,y1),(x2,y2),t):
return x1+t*(x2-x1),y1+t*(y2-y1)
def beziersplitatt(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)),t):
m1=tpoint((bx0,by0),(bx1,by1),t)
m2=tpoint((bx1,by1),(bx2,by2),t)
m3=tpoint((bx2,by2),(bx3,by3),t)
m4=tpoint(m1,m2,t)
m5=tpoint(m2,m3,t)
m=tpoint(m4,m5,t)
return ((bx0,by0),m1,m4,m),(m,m5,m3,(bx3,by3))
'''
Approximating the arc length of a bezier curve
according to <http://www.cit.gu.edu.au/~anthony/info/graphics/bezier.curves>
if:
L1 = |P0 P1| +|P1 P2| +|P2 P3|
L0 = |P0 P3|
then:
L = 1/2*L0 + 1/2*L1
ERR = L1-L0
ERR approaches 0 as the number of subdivisions (m) increases
2^-4m
Reference:
Jens Gravesen <gravesen@mat.dth.dk>
"Adaptive subdivision and the length of Bezier curves"
mat-report no. 1992-10, Mathematical Institute, The Technical
University of Denmark.
'''
def pointdistance((x1,y1),(x2,y2)):
return math.sqrt(((x2 - x1) ** 2) + ((y2 - y1) ** 2))
def Gravesen_addifclose(b, len, error = 0.001):
box = 0
for i in range(1,4):
box += pointdistance(b[i-1], b[i])
chord = pointdistance(b[0], b[3])
if (box - chord) > error:
first, second = beziersplitatt(b, 0.5)
Gravesen_addifclose(first, len, error)
Gravesen_addifclose(second, len, error)
else:
len[0] += (box / 2.0) + (chord / 2.0)
def bezierlengthGravesen(b, error = 0.001):
len = [0]
Gravesen_addifclose(b, len, error)
return len[0]
# balf = Bezier Arc Length Function
balfax,balfbx,balfcx,balfay,balfby,balfcy = 0,0,0,0,0,0
def balf(t):
retval = (balfax*(t**2) + balfbx*t + balfcx)**2 + (balfay*(t**2) + balfby*t + balfcy)**2
return math.sqrt(retval)
def Simpson(f, a, b, n_limit, tolerance):
n = 2
multiplier = (b - a)/6.0
endsum = f(a) + f(b)
interval = (b - a)/2.0
asum = 0.0
bsum = f(a + interval)
est1 = multiplier * (endsum + (2.0 * asum) + (4.0 * bsum))
est0 = 2.0 * est1
#print multiplier, endsum, interval, asum, bsum, est1, est0
while n < n_limit and abs(est1 - est0) > tolerance:
n *= 2
multiplier /= 2.0
interval /= 2.0
asum += bsum
bsum = 0.0
est0 = est1
for i in xrange(1, n, 2):
bsum += f(a + (i * interval))
est1 = multiplier * (endsum + (2.0 * asum) + (4.0 * bsum))
#print multiplier, endsum, interval, asum, bsum, est1, est0
return est1
def bezierlengthSimpson(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)), tolerance = 0.001):
global balfax,balfbx,balfcx,balfay,balfby,balfcy
ax,ay,bx,by,cx,cy,x0,y0=bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)))
balfax,balfbx,balfcx,balfay,balfby,balfcy = 3*ax,2*bx,cx,3*ay,2*by,cy
return Simpson(balf, 0.0, 1.0, 4096, tolerance)
def beziertatlength(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)), l = 0.5, tolerance = 0.001):
global balfax,balfbx,balfcx,balfay,balfby,balfcy
ax,ay,bx,by,cx,cy,x0,y0=bezierparameterize(((bx0,by0),(bx1,by1),(bx2,by2),(bx3,by3)))
balfax,balfbx,balfcx,balfay,balfby,balfcy = 3*ax,2*bx,cx,3*ay,2*by,cy
t = 1.0
tdiv = t
curlen = Simpson(balf, 0.0, t, 4096, tolerance)
targetlen = l * curlen
diff = curlen - targetlen
while abs(diff) > tolerance:
tdiv /= 2.0
if diff < 0:
t += tdiv
else:
t -= tdiv
curlen = Simpson(balf, 0.0, t, 4096, tolerance)
diff = curlen - targetlen
return t
#default bezier length method
bezierlength = bezierlengthSimpson
if __name__ == '__main__':
#print linebezierintersect(((,),(,)),((,),(,),(,),(,)))
#print linebezierintersect(((0,1),(0,-1)),((-1,0),(-.5,0),(.5,0),(1,0)))
tol = 0.00000001
curves = [((0,0),(1,5),(4,5),(5,5)),
((0,0),(0,0),(5,0),(10,0)),
((0,0),(0,0),(5,1),(10,0)),
((-10,0),(0,0),(10,0),(10,10)),
((15,10),(0,0),(10,0),(-5,10))]
'''
for curve in curves:
timing.start()
g = bezierlengthGravesen(curve,tol)
timing.finish()
gt = timing.micro()
timing.start()
s = bezierlengthSimpson(curve,tol)
timing.finish()
st = timing.micro()
print g, gt
print s, st
'''
for curve in curves:
print beziertatlength(curve,0.5)
# vim: expandtab shiftwidth=4 tabstop=8 softtabstop=4 fileencoding=utf-8 textwidth=99
|
