Even-Odd Fill Rule

[habakuk]

Subject: Help Needed with Even-Odd Fill Rule for Maurer Rose Animation

Hello DrawBot Community,

Me and my imaginary friend (AI) are reaching out for human intellignce once again. I'm currently working on creating an animated Moire Effect based on a Maurer Rose using DrawBot and have encountered an issue with applying the even-odd fill rule. The animation is supposed to alternate fills correctly to mimic the visual effect seen in examples like the one on this website. https://www.sqrt.ch/Buch/Maurer/maurerrosesanim.html However, doe to the missing even-odd filling rule, we haven't been able to achieve the desired effect.

Here's what I’ve tried so far:

Initial Attempt Without Even-Odd Fill Rule: (be carefull running this script, it takes ages to render. reduce the z variable to a low prime number)

# Parameters for the Maurer Rose
n = 5
d = 1
z = 853
ms = 90
dStroke = 1
dFarbe = (0, 0, 1)  # Blue stroke color
cFarbe = (1, 0, 0)  # Red fill color 

newDrawing()

for frame in range(z):
    newPage(1010, 1010)
    frameDuration(ms / 1000)
    translate(width() / 2, height() / 2)

    fill(0)
    rect(-width() / 2, -height() / 2, width(), height())

    path = BezierPath()
    for theta in range(z + 1):
        k = (theta * d * 2 * pi) / z
        r = -500 * sin(n * k)
        x = r * cos(k)
        y = r * sin(k)
        if theta == 0:
            path.moveTo((x, y))
        else:
            path.lineTo((x, y))

    path.closePath()

    fill(*cFarbe)
    drawPath(path)

    stroke(*dFarbe)
    strokeWidth(dStroke)
    lineJoin('round')
    drawPath(path)

    d += 1

saveImage("maurer_rose_animation.gif")
endDrawing()

Attempt Without Unsupported Methods:

# Draw the fill and stroke
def draw_maurer_rose(d, n, z, dStroke, dFarbe, cFarbe):
    path = BezierPath()
    for theta in range(z + 1):
        k = (theta * d * 2 * pi) / z
        r = -500 * sin(n * k)
        x = r * cos(k)
        y = r * sin(k)
        if theta == 0:
            path.moveTo((x, y))
        else:
            path.lineTo((x, y))
    path.closePath()

    fill(*cFarbe)
    drawPath(path)

    stroke(*dFarbe)
    strokeWidth(dStroke)
    lineJoin('round')
    drawPath(path)

# Animation loop
for frame in range(z):
    newPage(1010, 1010)
    frameDuration(ms / 1000)
    translate(width() / 2, height() / 2)

    fill(1)
    rect(-width() / 2, -height() / 2, width(), height())

    draw_maurer_rose(d, n, z, dStroke, dFarbe, cFarbe)

    d += 1

saveImage("maurer_rose_animation.gif")
endDrawing()

...despite several attempts, I haven't been able to achieve the desired even-odd fill rule effect. I would appreciate any guidance or suggestions on how to properly implement the even-odd fill rule for this animation in DrawBot.

Thank you in advance for your help!

[monomonnik]

Maybe this post can help you on your way?

[habakuk]

Hey @monomonnik
The problem is, that the rose is made of a single path and not two overlapping objects. I hoped there is some kind of a blend mode to clear overlapping colors.

[monomonnik]

You are correct, I should have looked better.

I don’t know if there exist these kind of filters for DrawBot (I assume you mean something like Illustrator’s Pathfinder tool).

I did some reading on the underlying NSBezierPath, which has an even-odd winding rule, but I'm not smart enough to figure out if that's useable, let alone how.