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This is more of a generic question to be honest, just wondering if anyone has done any sort of research on the subject.

Basically I am adding event support to a small game engine I am creating for my own personal use. I would like pixel perfect hover over 2d object event support and am just thinking of the best way of doing it. Realistically it would be faster for me personally just to invoke a draw of my objects onto a transparent canvas and checking if the mouse x y is over a transparent pixel or not since I dont have to make a set of points defining the outside of an object. This would also allow me to have holes in my object and it would still correctly know if I hovered over or not.

What I am wondering is using methods shown here: How can I determine whether a 2D Point is within a Polygon?

How much slower would my method be to the methods shown there?

Im currently still learning so its not easy for me to implement all of this and just test it myself since it would probably take me ages to get to work correctly and test the speeds.

Side note: I would still have a basic bounding box to save it from redrawing and testing every single time.

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Tom C
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1 Answers1

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Checking if a point is in a polygon will 99.999999% of the time be vastly, vastly faster.

To be slower the polygon would need to be extremely complex.

To do the other method you need to use getImageData, and getting image data on the canvas is very slow.

Point in polygon algorithms do properly account for holes. Make sure you have one that obeys the non-zero winding number rule, because that is what canvas uses (as opposed to the even odd rule) and you may want compatibility with paths constructed in the canvas (either now or later).

Simon Sarris
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