Rough PIL draw.arc() replacement that supports a line width.

pil_arc.py

def arc(draw, bbox, start, end, fill, width=1, segments=100):
    """
    Hack that looks similar to PIL's draw.arc(), but can specify a line width.
    """
    # radians
    start *= math.pi / 180
    end *= math.pi / 180

    # angle step
    da = (end - start) / segments

    # shift end points with half a segment angle
    start -= da / 2
    end -= da / 2

    # ellips radii
    rx = (bbox[2] - bbox[0]) / 2
    ry = (bbox[3] - bbox[1]) / 2

    # box centre
    cx = bbox[0] + rx
    cy = bbox[1] + ry

    # segment length
    l = (rx+ry) * da / 2.0

    for i in range(segments):

        # angle centre
        a = start + (i+0.5) * da

        # x,y centre
        x = cx + math.cos(a) * rx
        y = cy + math.sin(a) * ry

        # derivatives
        dx = -math.sin(a) * rx / (rx+ry)
        dy = math.cos(a) * ry / (rx+ry)

        draw.line([(x-dx*l,y-dy*l), (x+dx*l, y+dy*l)], fill=fill, width=width)