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# Name: bezier.py
# Package: wx.lib.pdfviewer
#
# Purpose: Compute Bezier curves for PDF rendered using wx.DC
# Adapted from the original source code, see below.
#
# Author: David Hughes dfh@forestfield.co.uk
# Copyright: Forestfield Software Ltd
# Licence: Public domain
# History: Created 17 Jun 2009
#
#----------------------------------------------------------------------------
import wx
from vec2d import *
def calculate_bezier(p, steps = 30):
"""
Calculate a bezier curve from 4 control points and return a
list of the resulting points.
Depends on the 2d vector class from http://www.pygame.org/wiki/2DVectorClass
2007 Victor Blomqvist
Released to the Public Domain
The function uses the forward differencing algorithm described at
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
def compute_points(controlpoints, nsteps=30):
""" Input 4 control points as wxRealPoints and convert to vec2d instances.
compute the nsteps points on the resulting curve and return them
as a list of wxPoints """
controlvectors = []
for p in controlpoints:
controlvectors.append(vec2d(p.x, p.y))
pointvectors = calculate_bezier(controlvectors, nsteps)
curvepoints = []
for v in pointvectors:
curvepoints.append(wx.Point(v[0], v[1]))
return curvepoints
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