Fix function _is_point_in_polygon()#19924
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TurboGit merged 2 commits intodarktable-org:masterfrom Feb 7, 2026
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The previous implementation of the ray casting algorithm did not handle
a special corner case correctly. If there are two consecutive line
segments of the polygon's edge represented by three consecutive corners
and the intermediate corner has the same latitude as the point to be
checked, i.e., `pt->lat == lat`, this condition was true for both line
segments. Instead, this condition should only be true for one of the two
line segments.
The condition should be
if(!(((lat1 > pt->lat) && (lat2 > pt->lat)) ||
((lat1 <= pt->lat) && (lat2 <= pt->lat))
which is equivalent to
if((lat1 > pt->lat) != (lat2 > pt-lat))
See the reference implementation of the even-odd rule at
https://en.wikipedia.org/w/index.php?title=Even%E2%80%93odd_rule&oldid=1274993919
for instance.
This modification avoids division by very small values `lat2 - lat1`, in case `lat1 ≈ lat2`. See the reference implementation of the even-odd rule at https://en.wikipedia.org/w/index.php?title=Even%E2%80%93odd_rule&oldid=1274993919 for instance.
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@codecrusher64 : Needs a release note entry, TIA. |
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This is a bugfix for issue #19843.