modified lib GPC for header only

worked on 3d traytracing

geo/BBox3.h

@@ -18,11 +18,16 @@ private:
 
 public:
 
-        /** empty ctor */
+	/** empty ctor */
 	BBox3() : p1(MAX,MAX,MAX), p2(MIN,MIN,MIN) {;}
 
-        /** ctor with min and max */
-        BBox3(const Point3 min, const Point3 max) : p1(min), p2(max) {;}
+	/** ctor with min and max */
+	BBox3(const Point3 min, const Point3 max) : p1(min), p2(max) {;}
+
+	/** create a bbox around the given point */
+	static BBox3 around(const Point3 center, const Point3 size) {
+		return BBox3(center-size/2, center+size/2);
+	}
 
 	/** adjust the bounding-box by adding this point */
 	void add(const Point3& p) {