Comments on: A quick note on line and segment intersection (as3)

By: James

James — Mon, 07 Feb 2011 07:07:36 +0000

I have done some performance tests on the original, this version, and the version below. I can’t remember where I found this code, but it seems to be slightly more efficient than Keith’s one when an intersection is found. If no intersection is found, it’s more than twice as fast.

public function intersectsLine(A:Point, B:Point, E:Point, F:Point):Point
{
var bx:int = B.x – A.x;
var by:int = B.y – A.y;
var dx:int = F.x – E.x;
var dy:int = F.y – E.y;
var b_dot_d_perp:Number = bx * dy – by * dx;
if(b_dot_d_perp == 0) {
return null;
}
var cx:int = E.x – A.x;
var cy:int = E.y – A.y;
var t:Number = (cx * dy – cy * dx) / b_dot_d_perp;
if(t 1) {
return null;
}
var u:Number = (cx * by – cy * bx) / b_dot_d_perp;
if(u 1) {
return null;
}
return new Point(A.x+t*bx, A.y+t*by);
}

By: basics in generative art 7 : USEFUL TOOLS « HIDIHO!

basics in generative art 7 : USEFUL TOOLS « HIDIHO! — Wed, 29 Dec 2010 22:31:05 +0000

[...] I found it and/or who wrote it, I usually mention it. anyway, at least Keith Peters, Keith Hair and Hristo Dachev have to be [...]

By: basics in generative art 5 : join the dots « HIDIHO!

basics in generative art 5 : join the dots « HIDIHO! — Mon, 27 Dec 2010 17:21:25 +0000

[...] the intersection method was done by Keith Hair and improved by Hristo Dachev. [...]

By: hristo

hristo — Thu, 17 Jun 2010 10:28:58 +0000

Hey Jack,
I see your point – I’ll look into it when I have some time, but sounds like bigtime rounding errors.
What sort of app runs into this kind of trouble ???? :)
Thanks for the comment

By: Jack

Jack — Fri, 28 May 2010 05:25:23 +0000

nice function! I’ve used it in my application, and found a small bug with (almost) horizontal and vertical line segments:

where
A = (3.0999999999999996, 3.1499999999999995)
B = (5, 3.15)

E = (3.1499999999999995, 5.8500000000000005)
F = (3.1499999999999995, 3.0999999999999996)

and
ip = (3.1499999999999995, 3.149999999999999)

this line executes and returns null:
if ( ( A.y < B.y ) ? ip.y B.y : ip.y > A.y || ip.y A.y

By: Mathieu Gosselin

Mathieu Gosselin — Sun, 06 Sep 2009 11:27:57 +0000

Great!
You can’t know how useful it is to me! ;-)