diff -r 6de5ac1fb471 -r 3a9e761e4faa src/linetypes/triangle.cpp
--- a/src/linetypes/triangle.cpp	Sun Jan 19 14:25:57 2020 +0200
+++ b/src/linetypes/triangle.cpp	Wed Jan 22 00:23:29 2020 +0200
@@ -68,5 +68,12 @@
 		this->points[1],
 		this->points[2],
 		this->colorIndex,
-		this->id));
+			this->id));
 }
+
+void linetypes::Triangle::invert()
+{
+	//    0 1 2
+	// -> 1 0 2
+	std::swap(this->points[0], this->points[1]);
+}