how to fill a part of a circle using PIL?

Question

hello.

I'm trying to use PIL for a task but the result is very dirty.

What I'm doing is trying to fill a part of a piece of a circle, as you can see on the image.

Here is my code:

def gen_image(values):

    side = 568
    margin = 47
    image = Image.open(settings.MEDIA_ROOT + "/i/promo_circle.jpg")

    draw = ImageDraw.Draw(image)
    draw.ellipse((margin, margin, side-margin, side-margin), outline="white")

    center = side/2
    r = side/2 - margin

    cnt = len(values)

    for n in xrange(cnt):
        angle = n*(360.0/cnt) - 90
        next_angle = (n+1)*(360.0/cnt) - 90
        nr = (r * values[n] / 5)

        max_r = r
        min_r = nr

        for cr in xrange(min_r*10, max_r*10):
            cr = cr/10.0
            draw.arc((side/2-cr, side/2-cr, side/2+cr, side/2+cr), angle, next_angle, fill="white")

    return image

Answer 1

It's been a while since I used PIL, but in various other graphics libraries, there's often an aliasing problem when drawing arcs.

Have you tried enabling anti-aliasing or drawing with thicker lines?

[Edit] Having a quick look over the PIL library, I think you're right about line width etc.

Sounds like the easiest thing to do here is to build up a polygon which covers each area. So a pair of points at each end and then a load round the middle to stop the edges looking jagged. Does that make sense?

Answer 2

Instead of erasing with white, consider drawing a mask of just the areas you want to show. Here's an example of this for a circular mask.

http://stackoverflow.com/questions/890051/how-do-i-generate-circuar-thumbnails-with-pil