Objective-C reference counting error when applying filters.

[typesupply]

FYI, I found an issue in PyObjC that pertains to DrawBot: ronaldoussoren/pyobjc#649 (comment)

I first encountered this error in DrawBot before I moved to running from the commandline. This script will trigger the issue in DrawBot:

import drawBot as bot

steps = 20
step = 50
imageWidth = step * steps
imageHeight = imageWidth
imageRect = (0, 0, imageWidth, imageHeight)

sections = []
for x in range(steps):
    x *= step
    for y in range(steps):
        y *= step
        sections.append((x, y, step, step))

def sampleImage():
    image = bot.ImageObject()

    with image:
        bot.size(imageWidth, imageHeight)
        bot.fill(1, 1, 1, 1)
        bot.rect(*imageRect)
        bot.fill(0, 0, 0, 1)
        path = bot.BezierPath()
        path.oval(*imageRect)
        bot.drawPath(path)

    samples = {}

    for section in sections:
        i = image.copy()
        i.areaAverage(section)
        color = bot.imagePixelColor(i, (0, 0))
        samples[section] = color

    return image

for i in range(100):
    print(f"try {i}...")
    sampleImage()

As Ronald suggested, wrapping the for section in sections in with objc.autorelease_pool(): solves the problem. I don't know if you want to wrap the bitmap representation code in this or leave it up to the user.

[justvanrossum]

Ideally this would be integrated in DrawBot. However, playing with this, I can't get it to work with individual autorelease pools around individual lines in the section loop, so I don't see how we could accomplish it :(

[typemytype]

If I read it correctly the counting error only happens on applying filters to an image?

in that case we could wrap imageObject._applyFilters https://github.com/typemytype/drawbot/blob/master/drawBot/context/tools/imageObject.py#L213