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I am trying to figure out the correct order between edges on edge table on scan line polygon fill.

One example here on Y=1 takes first AB line enter image description here

And another example takes on Y=0 v1v0. enter image description here

I cannot understand why not AB instead of BA and why v1v0 instead of v0v1 respectively

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  • $\begingroup$ Why AB instead of BA? Presumably because the polygon is being defined in anticlockwise order and so all edges are labelled accordingly. In fact, it is important to keep things consistent, especially when creating the edge equations. This is to avoid 'holes' or 'double filling' of pixels when handling "tie-break" cases when the centre of a pixel lies 'exactly' on an edge. $\endgroup$
    – Simon F
    Commented Sep 4, 2017 at 8:31

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