Add is_null_vector() function

src/vector.c

@@ -184,3 +184,24 @@ bool set_null_vector(vector *a)
 	return true;
 
 }
+
+/**
+ * Check if vector a is a null vector,
+ * so all coordinates are 0.
+ *
+ * @param a vector
+ * @return true if vector is a null vector, false
+ * otherwise, -1 on failure
+ */
+int is_null_vector(vector *a)
+{
+	if (!a)
+		return -1;
+
+	if (a->x == 0 &&
+			a->y == 0 &&
+			a->z == 0)
+		return true;
+	else
+		return false;
+}

src/vector.h

@@ -123,6 +123,7 @@ bool sub_vectors(vector *a, vector *b, vector *c);
 bool normalize_vector(vector *a, vector *b);
 bool copy_vector(vector *a, vector *b);
 bool set_null_vector(vector *a);
+int is_null_vector(vector *a);
 
 
 #endif /* _DROW_ENGINE_VEC_MATH_H */