Keith Hair » Behind http://keith-hair.net/blog Scripting is fun like any other hobby Mon, 17 May 2010 16:02:22 +0000 en hourly 1 http://wordpress.org/?v=3.0 Knowing if a Point is behind a Line http://keith-hair.net/blog/2009/05/27/knowing-if-a-point-is-behind-a-line/ http://keith-hair.net/blog/2009/05/27/knowing-if-a-point-is-behind-a-line/#comments Wed, 27 May 2009 21:15:01 +0000 Keith H http://keith-hair.net/blog/?p=58 Yea yea, I know Battlestar Galactica is over, but today I thought of the "Daybreak part 1" episode of BSG.
Hera, a little girl has been kidnapped by the Cylons. As part of a desperate plan to save Hera, Admiral Adama draws a red line on the deck, and asks for those willing to risk their lives to save her, do so by crossing the line.

I had a similar problem also with my scripts. I wanted to simply know if a Point was behind a Line or not... :) 

 
/*-----------------------------------------------------------------
Returns true if Point P is behind line defined by Points C and D.
 ----------------------------------------------------------------*/
function isBehindLine(P:Point,C:Point,D:Point):Boolean
{
	var a:Number=Point.distance(P,C.add(Point.polar(1,Math.atan2(C.y - D.y,C.x - D.x) + Math.PI / 2)));
	var b:Number=Point.distance(P,C.add(Point.polar(-1,Math.atan2(C.y - D.y,C.x - D.x) + Math.PI / 2)));
	return a < b;
}
 
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