Captcha in nimrod

captcha.nim

import cairo, math

# adapted from https://github.com/benkasminbullock/image-png-cairo/blob/master/examples/captcha.pl
# live example: http://www.lemoda.net/png/png-cairo-captcha/index.html

const xsize = 200
const ysize = 50
const gap = 10

proc create_captcha(text: string) =
    var surface = image_surface_create(FORMAT_ARGB32, xsize, ysize)
    var cr = create(surface)

    # background
    cr.set_source_rgb(0, 0, 0)
    cr.rectangle(0, 0, xsize, ysize)
    cr.fill()


    # captcha text
    cr.set_source_rgb(1, 1, 1)
    cr.set_font_size(ysize - gap)
    cr.move_to(gap, ysize - gap)
    cr.show_text(text)
    cr.fill()

    # translucent circles
    for i in 0 .. 50:
        cr.set_source_rgba(random(1.0), random(1.0), random(1.0), 0.4)
        cr.arc(float(random(xsize)), float(random(ysize)),
               random(25.0), 0, 2 * PI)
        cr.fill()

    cr.destroy()
    discard write_to_png(surface, "test.png")

when isMainModule:
    var text = "abcdef?"
    create_captcha(text)