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From: bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: Re: filling area by color atack safety
Date: Sun, 17 Mar 2024 12:49:33 +0000
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On 17/03/2024 12:28, Malcolm McLean wrote:
> On 17/03/2024 10:31, Ben Bacarisse wrote:
>> scott@slp53.sl.home (Scott Lurndal) writes:
>>
>>> David Brown <david.brown@hesbynett.no> writes:
>>>> On 16/03/2024 12:33, Malcolm McLean wrote:
>>>
>>>>> And here's some code I wrote a while ago. Use that as a pattern. 
>>>>> But not
>>>>> sure how well it works. Haven't used it for a long time.
>>>>>
>>>>> https://github.com/MalcolmMcLean/binaryimagelibrary/blob/master/drawbinary.c
>>>>>
>>>>
>>>> Your implementation is a mess, /vastly/ more difficult to prove correct
>>>
>>> Malcolm can't even spell 'integer' correctly in that code blob :-).
>>
>> As someone with dyslexia I have never liked mocking remarks about
>> spelling errors.  Using "even" suggests that a superficial issue hints
>> at deeper problems.  This is rarely the case.
>>
>> However, I /would/ urge Malcolm to correct the spelling if Bresenham
>> since the intent was clearly to credit the discoverer.  Also,
>> misspellings don't play well with library databases.
>>
>>> Certainly the intent of Fir's algorithm is easily discerned from
>>> his code.   I can't say that about Malcolms.
>>
>> I have some reservations about the code, but he posted a link so there
>> is no indication that he wants a review of it.
>>
> Tbe main intent was to help fir. That algorithm does tend to blow the 
> stack though of course it depends on the image. However worst case is a 
> pattern which is pixel wide line, e.g. a spiral or a maze or a series of 
> alterante light and dark bands with a lirtel gaps at each end. And you 
> achieve that by filling half the pixels. So foe a 100x100 image your 
> worst case is 10,000 = 5,000 recursive calls, and the stack is blown.

I'd been planning to create a square spiral. But I found I got N*N/2 
behaviour even with a blank image which was filled in from one corner.

After thinking about it, it became obvious that the potential call depth 
wasn't the distance to a boundary in any direction, but the number of 
pixels in the area to be eventually filled in, which could be a big 
chunk of the N*N total.