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I'm developing a game in HTML5 and JavaScript using Canvas API for drawing graphics. I want to detect if the user has clicked on a bezier curve which has the line width of 20 pixels (something like this one on the picture). I need to validate if the user has clicked on the area drawn by the curve (red and black).

I implemented such an algorithm for lines, but could not adapt it to quadratic and cubic bezier curves. So I need an algorithm that will compare the position of a point relative to a bezier curve which has the form of

B(t) = P0(1-t)2 + P1(1-t)t + P2t2


B(t) = P0(1-t)3 + 3*P1(1-t)t + 3*P2(1-t)t2 + P3t3

and say if it is in the neighborhood of the bezier curve's path, I mean on the black drawn area. enter image description here

[Red: Bezier curve's path; Black: Bezier curve's drawb area]

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1 Answer 1


In particular, The last answer on the page gives this link, which I thought explained it fairly clearly:


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Thanks, sometimes it's difficult to define something what you need to search :) now, I'll need to digest a lot of math –  micnic Aug 5 '12 at 7:30

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