1 files changed, 25 insertions, 0 deletions
diff --git a/experimental/Intersection/LineUtilities.cpp b/experimental/Intersection/LineUtilities.cpp
index 13942252d9..38e1ba0c1f 100644
--- a/experimental/Intersection/LineUtilities.cpp
+++ b/experimental/Intersection/LineUtilities.cpp
@@ -30,3 +30,28 @@ void sub_divide(const _Line& line, double t1, double t2, _Line& dst) {
     dst[1].x = line[0].x - t2 * delta.x;
     dst[1].y = line[0].y - t2 * delta.y;
 }
+
+// may have this below somewhere else already: 
+// copying here because I thought it was clever
+
+// Copyright 2001, softSurfer (www.softsurfer.com)
+// This code may be freely used and modified for any purpose
+// providing that this copyright notice is included with it.
+// SoftSurfer makes no warranty for this code, and cannot be held
+// liable for any real or imagined damage resulting from its use.
+// Users of this code must verify correctness for their application.
+
+// Assume that a class is already given for the object:
+//    Point with coordinates {float x, y;}
+//===================================================================
+
+// isLeft(): tests if a point is Left|On|Right of an infinite line.
+//    Input:  three points P0, P1, and P2
+//    Return: >0 for P2 left of the line through P0 and P1
+//            =0 for P2 on the line
+//            <0 for P2 right of the line
+//    See: the January 2001 Algorithm on Area of Triangles
+float isLeft( _Point P0, _Point P1, _Point P2 )
+{
+    return (P1.x - P0.x)*(P2.y - P0.y) - (P2.x - P0.x)*(P1.y - P0.y);
+}