reportlab/pdfgen/pdfgeom.py
author rgbecker
Wed, 25 Oct 2000 08:57:46 +0000
changeset 494 54257447cfe9
parent 47 0505ed9b16d9
child 562 6c9408ec3302
permissions -rwxr-xr-x
Changed to indirect copyright

#copyright ReportLab Inc. 2000
#see license.txt for license details
#history http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/reportlab/pdfgen/pdfgeom.py?cvsroot=reportlab
#$Header: /tmp/reportlab/reportlab/pdfgen/pdfgeom.py,v 1.6 2000/10/25 08:57:45 rgbecker Exp $
__version__=''' $Id: pdfgeom.py,v 1.6 2000/10/25 08:57:45 rgbecker Exp $ '''
__doc__="""
This module includes any mathematical methods needed for PIDDLE.
It should have no dependencies beyond the Python library.

So far, just Robert Kern's bezierArc.

"""

from math import sin, cos, pi, ceil

def bezierArc(x1,y1, x2,y2, startAng=0, extent=90):
    """bezierArc(x1,y1, x2,y2, startAng=0, extent=90) --> List of Bezier
curve control points.

(x1, y1) and (x2, y2) are the corners of the enclosing rectangle.  The
coordinate system has coordinates that increase to the right and down.
Angles, measured in degress, start with 0 to the right (the positive X
axis) and increase counter-clockwise.  The arc extends from startAng
to startAng+extent.  I.e. startAng=0 and extent=180 yields an openside-down
semi-circle.

The resulting coordinates are of the form (x1,y1, x2,y2, x3,y3, x4,y4)
such that the curve goes from (x1, y1) to (x4, y4) with (x2, y2) and
(x3, y3) as their respective Bezier control points."""

    x1,y1, x2,y2 = min(x1,x2), max(y1,y2), max(x1,x2), min(y1,y2)

    if abs(extent) <= 90:
        arcList = [startAng]
        fragAngle = float(extent)
        Nfrag = 1
    else:
        arcList = []
        Nfrag = int(ceil(abs(extent)/90.))
        fragAngle = float(extent) / Nfrag

    x_cen = (x1+x2)/2.
    y_cen = (y1+y2)/2.
    rx = (x2-x1)/2.
    ry = (y2-y1)/2.
    halfAng = fragAngle * pi / 360.
    kappa = abs(4. / 3. * (1. - cos(halfAng)) / sin(halfAng))

    if fragAngle < 0:
        sign = -1
    else:
        sign = 1
    
    pointList = []

    for i in range(Nfrag):
        theta0 = (startAng + i*fragAngle) * pi / 180.
        theta1 = (startAng + (i+1)*fragAngle) *pi / 180.
        if fragAngle > 0:
            pointList.append((x_cen + rx * cos(theta0),
                              y_cen - ry * sin(theta0),
                              x_cen + rx * (cos(theta0) - kappa * sin(theta0)),
                              y_cen - ry * (sin(theta0) + kappa * cos(theta0)),
                              x_cen + rx * (cos(theta1) + kappa * sin(theta1)),
                              y_cen - ry * (sin(theta1) - kappa * cos(theta1)),
                              x_cen + rx * cos(theta1),
                              y_cen - ry * sin(theta1)))
        else:
            pointList.append((x_cen + rx * cos(theta0),
                              y_cen - ry * sin(theta0),
                              x_cen + rx * (cos(theta0) + kappa * sin(theta0)),
                              y_cen - ry * (sin(theta0) - kappa * cos(theta0)),
                              x_cen + rx * (cos(theta1) - kappa * sin(theta1)),
                              y_cen - ry * (sin(theta1) + kappa * cos(theta1)),
                              x_cen + rx * cos(theta1),
                              y_cen - ry * sin(theta1)))

    return pointList