Keith Hair

"Drag and Drop" behavior is easy to do in ActionScript, but sometimes it would be cooler if you could limit or constrain the dragging movement of an object to a line. This opens the door for implementing
more creative interaction design...

 
/*---------------------------------------------------------------------------
Returns the closest Point on Line "AB" to Point "p":
 
p			-Point, the Point to constrain to the line.
A			-Point, beginning Point of Line.
B			-Point, ending Point of Line.
as_seg	-Boolean, limits return Point between endpoints of A and B.
----------------------------------------------------------------------------*/
function constrainPointToLine(p:Point,A:Point,B:Point,as_seg:Boolean=false):Point
{
    var cp:Point=new Point();
    var dx:Number;
    var dy:Number;
    var t:Number;
 
    dx = B.x - A.x;
    dy = B.y - A.y;
    if (dx == 0 && dy == 0) {
        cp.x = A.x;
        cp.y = A.y;
    }else{
        t = ((p.x - A.x) * dx + (p.y - A.y) * dy) / (dx * dx + dy * dy);
        if (as_seg){
			t = Math.min(Math.max(0,t),1);
		}
        cp.x = A.x + t * dx;
        cp.y = A.y + t * dy;
    }
    return cp;
}
 

This entry was posted on Saturday, December 27th, 2008 at 1:42 pm and is filed under ActionScript 3.You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.