Fix #6

CppGame/Line.h

@@ -12,7 +12,7 @@ public:
 	Line(float x1, float y1, float x2, float y2);
 	Line(float x1,float y1,float x2, float y2,tuple_color color1, tuple_color color2);
 	static Line normalize(int x1, int y1, int x2, int y2,int width,int height,tuple_color color1, tuple_color color2);
-	float length() {
+	float length() const {
 		float dx = x1 - x2;
 		float dy = y1 - y2;
 		return sqrt(dx * dx + dy * dy);