I finally have a version that gives me the answer I need in all cases :)
Note that I removed the line that flips y and simplified B, d, and e.

public function getDistanceFromLine(a:Point, b:Point, c:Point, as_seg:Boolean = false):Object {
var obj:Object = new Object();
obj.dist = -1;
obj.poi = new Point();
if (a.x == b.x) {
obj.dist = Math.abs(a.x – c.x);
obj.poi.x = a.x;
obj.poi.y = c.y;
return obj;
}else if (a.y == b.y) {
obj.dist = Math.abs(a.y – c.y);
obj.poi.x = c.x;
obj.poi.y = a.y;
return obj;
}
var m:Number = (a.y – b.y) / (a.x – b.x);
var B:Number = 1 / m;
var d:Point = new Point(c.x + m, c.y);
var e:Point = new Point(c.x, c.y + B);
var poi:Point = lineIntersectLine(a, b, d, e, as_seg); // use Keith’s function to check for an intersection
if(poi != null){
var dx:Number = poi.x – c.x;
var dy:Number = poi.y – c.y;
obj.dist = Math.pow(dx * dx + dy * dy, .5);
obj.poi = poi;
}
return obj;
}

Cheers,

Tomasz

public function getDistanceFromLine(a:Point,b:Point,c:Point,as_seg:Boolean=false):Object{
var obj:Object = new Object();
obj.dist = -1;
obj.poi = new Point();
if (a.x == b.x) {
obj.dist = Math.abs(a.x – c.x);
obj.poi.x = a.x;
obj.poi.y = c.y;
return obj;
}else if (a.y == b.y) {
obj.dist = Math.abs(a.y – c.y);
obj.poi.x = c.x;
obj.poi.y = a.y;
return obj;
}
var m:Number = (a.y – b.y) / (a.x – b.x);
var B:Number = (1 / m) * c.x – c.y;
var d:Point = new Point(b.x, b.x * ( -1 / m) + B);
var e:Point = new Point(a.x, a.x * ( -1 / m) + B);
var poi:Point = lineIntersectLine(a, b, d, e, as_seg); // use Keith’s function to check for an intersection
if(poi != null){
var dx:Number = poi.x – c.x;
var dy:Number = poi.y + c.y;
obj.dist = Math.pow(dx * dx + dy * dy, .5);
obj.poi = poi;
}
return obj;
}

Thanks again

public function getDistanceFromLine(a:Point,b:Point,c:Point,as_seg:Boolean=false):Object{
c.y *= -1; // flip for Flash
var obj:Object = new Object();
obj.dist = -1;
obj.pt = new Point();
var m:Number = (a.y – b.y) / (a.x – b.x);
var B:Number = (1 / m) * c.x – c.y;
var d:Point;
var e:Point;
if (m == Infinity || m == -Infinity)
{
d = new Point(c.x+1, c.y);
e = new Point(c.x-1, c.y);
}else if (B == Infinity || B == -Infinity)
{
d = new Point(c.x, c.y + 1);
e = new Point(c.x, c.y – 1);
}else
{
d = new Point(b.x, b.x * ( -1 / m) + B);
e = new Point(a.x, a.x * ( -1 / m) + B);
}
var poi:Point = lineIntersectLine(a, b, d, e, as_seg); // use Keith’s function to check for an intersection
if(poi != null){
var dx:Number = poi.x – c.x;
var dy:Number = poi.y + c.y;
obj.dist = Math.pow(dx * dx + dy * dy, .5);
obj.poi = poi;
}
return obj;
}

Thanks for sharing!

I was struggling to make your code work, so I went back to searching the internet, and found this much shorter function that does the same:

public function PointToLineDistance(p1:Point, p2:Point, p3:Point):Object
{
var xDelta:Number = p2.x – p1.x;
var yDelta:Number = p2.y – p1.y;
if ((xDelta == 0) && (yDelta == 0))
{
// p1 and p2 cannot be the same point
p2.x += 1;
p2.y += 1;
xDelta = 1;
yDelta = 1;
}
var u:Number = ((p3.x – p1.x) * xDelta + (p3.y – p1.y) * yDelta) / (xDelta * xDelta + yDelta * yDelta);
var closestPoint:Point;
var obj:Object = new Object;

if (u 1)
{
obj.dist = -1;
}
else
{
closestPoint = new Point(p1.x + u * xDelta, p1.y + u * yDelta);
obj.dist = Point.distance(closestPoint, new Point(p3.x, p3.y));
obj.closest = closestPoint;
}
return obj;
}