diff -r 2f79053c2e9a -r 47cb50cfa9ad src/ldrawalgorithm.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ldrawalgorithm.h	Fri Mar 04 23:00:06 2022 +0200
@@ -0,0 +1,22 @@
+#pragma once
+#include "modeleditor.h"
+
+namespace ldraw
+{
+	/// Determines how quadrilaterals are split into triangles
+	enum class Diagonal
+	{
+		Diagonal_13,
+		Diagonal_24
+	};
+
+	// Splits the specified quadrilateral into triangles.
+	// If it is not a quadrilateral then no action is performed
+	auto splitQuadrilateral(ModelEditor& editor,
+		quadrilateralid_t quadrilateral_id,
+		Diagonal splitType = Diagonal::Diagonal_13
+	) -> std::optional<std::pair<triangleid_t, triangleid_t>>;
+
+	void invert(ModelEditor& editor, ldraw::id_t id);
+	void makeUnofficial(ModelEditor &editor);
+}