Add DistanceToLine function

image/path/path.go

@@ -59,6 +59,21 @@ func Distance (start, end image.Point) float64 {
 	return math.Sqrt(float64(delta.X * delta.X) + float64(delta.Y * delta.Y))
 }
 
+// DistanceToLine calculates the distance from a point to a line which passes
+// through points line1 and line2.
+func DistanceToLine (point, line1, line2 image.Point) float64 {
+	x  := float64(point.X)
+	y  := float64(point.Y)
+	x1 := float64(line1.X)
+	y1 := float64(line1.Y)
+	x2 := float64(line2.X)
+	y2 := float64(line2.Y)
+	
+	triangle := math.Abs((y2 - y1)*x - (x2 - x1)*y + x2*y1 - y2*x1)
+	
+	return triangle / Distance(line1, line2)
+}
+
 func lerp (fac float64, x, y int) int {
 	return int(float64(x) * fac + float64(y) * (1.0 - fac))
 }