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Geek Culture / Is this right? (bresenham)

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NeX the Fairly Fast Ferret
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Posted: 12th Sep 2009 03:26 Edited at: 12th Sep 2009 03:27
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Here's a link to an "optimised" Bresenham line drawing algorithm on Wikipedia.

http://en.wikipedia.org/wiki/Bresenham's_line_algorithm#Optimization

At the beginning, it creates a bool called steep, and if it is true it swaps the X&Y. Then, there's another if statement during the plotting routine which swaps them right back.

Why?

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Phaelax
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Posted: 12th Sep 2009 07:00
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It looks fine to me. It only swaps back if x0 is greater than x1. It wants to keep x1 as the larger number.

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Jeff032
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Posted: 12th Sep 2009 07:13
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I believe he is referring to:



and then



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IanM
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Posted: 12th Sep 2009 13:04
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Quote: "Why?"

Because if it didn't pick the greater range for driving the loop, it would print a line of separated dots.

Implement the code as it has described and prove that it works at all line angles, then comment out that first step and run it again and you'll see the difference.

Utility plug-ins collection (updated 07/04/09) and
http://www.matrix1.demon.co.uk
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NeX the Fairly Fast Ferret
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Posted: 12th Sep 2009 13:08
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Hmm, I see. It needs to swap them around for the calculations but needs them in x:y format for plotting the point. Thanks.

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