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Handy piece of code

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johnhattan

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Here's a quick-n-simple piece of AS3 (or javascript) that calculates the point on a line closest to a given point. It took me a couple of tries to get it right, so I figured I would share it.

var nearestPtToLine = function(segA:Point, segB:Point, p:Point, infinite:Boolean = true):Point
{
var dx:Number = segB.x - segA.x
var dy:Number = segB.y - segA.y
var u:Number = ((p.x - segA.x) * dx + (p.y - segA.y) * dy) / (dx * dx + dy * dy)

if (!infinite)
{
if (u > [[1]])
u = [[1]]
else if (u < [[0]])
u = [[0]]
}
return new Point(segA.x + u * dx , segA.y + u * dy)
}




seg1 and seg2 define a line segment. p is the point to test. infinite assumes that the line extends beyond seg1 and seg2. If you need the distance from a point to a line, just use the distance function in the flash.geom.Point object.


EDIT: I don't know why gamedev's source formatter is putting brackets around the 1's and 0's in the if (!infinite) block. Don't do that. Just regular ones and zeros.
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