Produce PDF files, draw polygons with rounded corners

Question

What is the right tool for the job if I want to write a Python script that creates PDF vector graphics ? In particular, I need to draw filled polygons with rounded corners (i.e., Flat shapes consisting of straight and circular arcs ).

It seems that matplotlib makes it fairly easy to draw rounded rectangles and common acute-angled polygons. However, in order to draw rounded polygons, it seems that I must first compute a Bezier curve that approximates the shape.

Is there anything more direct available? Or is there another library that I can use to compute a Bezier curve that approaches the shape I want to create? Ideally, I would just indicate a pair (location, radius angle) for each vertex.

Here is an example: I would like to specify a red polygon (+ radius of each corner), and the library will display a gray image:

(For convex polygons, I could trick and use a thick pen to draw the outline of the polygon. However, this does not work in a non-convex case.)

Answer 1

PDF, cairo, libaray, "" " PDF-. Python.

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Answer 2

matplotlib. matplotlib Path Path.

#!/usr/bin/env python

import numpy as np
from matplotlib.path import Path
from matplotlib.patches import PathPatch, Polygon
from matplotlib.transforms import Bbox, BboxTransformTo

def side(a, b, c):
    "On which side of line a-b is point c? Returns -1, 0, or 1."
    return np.sign(np.linalg.det(np.c_[[a,b,c],[1,1,1]]))

def center((prev, curr, next), radius):
    "Find center of arc approximating corner at curr."
    p0, p1 = prev
    c0, c1 = curr
    n0, n1 = next
    dp = radius * np.hypot(c1 - p1, c0 - p0)
    dn = radius * np.hypot(c1 - n1, c0 - n0)
    p = p1 * c0 - p0 * c1
    n = n1 * c0 - n0 * c1
    results = \
        np.linalg.solve([[p1 - c1, c0 - p0],
                         [n1 - c1, c0 - n0]],
                        [[p - dp, p - dp, p + dp, p + dp],
                         [n - dn, n + dn, n - dn, n + dn]])
    side_n = side(prev, curr, next)
    side_p = side(next, curr, prev)
    for r in results.T:
        if (side(prev, curr, r), side(next, curr, r)) == (side_n, side_p):
            return r
    raise ValueError, "Cannot find solution"

def proj((prev, curr, next), center):
    "Project center onto lines prev-curr and next-curr."
    p0, p1 = prev = np.asarray(prev)
    c0, c1 = curr = np.asarray(curr)
    n0, n1 = next = np.asarray(next)
    pc = curr - prev
    nc = curr - next
    pc2 = np.dot(pc, pc)
    nc2 = np.dot(nc, nc)
    return (prev + np.dot(center - prev, pc)/pc2 * pc,
            next + np.dot(center - next, nc)/nc2 * nc)

def rad2deg(angle):
    return angle * 180.0 / np.pi

def angle(center, point):
    x, y = np.asarray(point) - np.asarray(center)
    return np.arctan2(y, x)

def arc_path(center, start, end):
    "Return a Path for an arc from start to end around center."
    # matplotlib arcs always go ccw so we may need to mirror
    mirror = side(center, start, end) < 0
    if mirror: 
        start *= [1, -1]
        center *= [1, -1]
        end *= [1, -1]
    return Path.arc(rad2deg(angle(center, start)),
                    rad2deg(angle(center, end))), \
           mirror

def path(vertices, radii):
    "Return a Path for a closed rounded polygon."
    if np.isscalar(radii):
        radii = np.repeat(radii, len(vertices))
    else:
        radii = np.asarray(radii)
    pv = []
    pc = []
    first = True
    for i in range(len(vertices)):
        if i == 0:
            seg = (vertices[-1], vertices[0], vertices[1])
        elif i == len(vertices) - 1:
            seg = (vertices[-2], vertices[-1], vertices[0])
        else:
            seg = vertices[i-1:i+2]
        r = radii[i]
        c = center(seg, r)
        a, b = proj(seg, c)
        arc, mirror = arc_path(c, a, b)
        m = [1,1] if not mirror else [1,-1]
        bb = Bbox([c, c + (r, r)])
        iter = arc.iter_segments(BboxTransformTo(bb))
        for v, c in iter:
            if c == Path.CURVE4:
                pv.extend([m * v[0:2], m * v[2:4], m * v[4:6]])
                pc.extend([c, c, c])
            elif c == Path.MOVETO:
                pv.append(m * v)
                if first:
                    pc.append(Path.MOVETO)
                    first = False
                else:
                    pc.append(Path.LINETO)
    pv.append([0,0])
    pc.append(Path.CLOSEPOLY)

    return Path(pv, pc)

if __name__ == '__main__':
    from matplotlib import pyplot
    fig = pyplot.figure()
    ax = fig.add_subplot(111)
    vertices = [[3,0], [5,2], [10,0], [6,9], [6,5], [3, 5], [0,2]]

    patch = Polygon(vertices, edgecolor='red', facecolor='None',
                    linewidth=1)
    ax.add_patch(patch)

    patch = PathPatch(path(vertices, 0.5), 
                      edgecolor='black', facecolor='blue', alpha=0.4,
                      linewidth=2)
    ax.add_patch(patch)

    ax.set_xlim(-1, 11)
    ax.set_ylim(-1, 9)
    fig.savefig('foo.pdf')