diff -r 6988973515d2 -r ca23936b455b src/ldrawalgorithm.cpp
--- a/src/ldrawalgorithm.cpp	Wed May 25 20:36:34 2022 +0300
+++ b/src/ldrawalgorithm.cpp	Mon Jun 06 22:01:22 2022 +0300
@@ -1,53 +1,26 @@
 #include "ldrawalgorithm.h"
-#include "linetypes/quadrilateral.h"
-#include "linetypes/triangle.h"
 
-void ldraw::invert(ModelEditor& editor, ldraw::id_t id, GetPolygonsContext* context)
+std::pair<Triangle, Triangle> splitTriangles(
+	const Quadrilateral& q,
+	ldraw::Diagonal diagonal)
 {
-	editor.modifyObject(id, [context](ldraw::Object* object){
-		object->invert(context);
-	});
-}
-
-static std::array<geom::Triangle, 2> splitTriangles(ldraw::Diagonal diagonal, const std::array<glm::vec3, 4>& points)
-{
-	std::array<geom::Triangle, 2> result;
+	std::pair<Triangle, Triangle> result;
 	switch (diagonal)
 	{
 	case ldraw::Diagonal::Diagonal_13:
-		result = {geom::Triangle{points[0], points[1], points[2]}, {points[0], points[2], points[3]}};
+		result = {Triangle{q.p1, q.p2, q.p3}, {q.p1, q.p3, q.p4}};
 		break;
 	case ldraw::Diagonal::Diagonal_24:
-		result = {geom::Triangle{points[0], points[1], points[3]}, {points[1], points[2], points[3]}};
+		result = {Triangle{q.p1, q.p2, q.p3}, {q.p2, q.p3, q.p4}};
 		break;
 	}
 	return result;
 }
 
-auto ldraw::splitQuadrilateral(
-	ModelEditor& editor,
-	ldraw::quadrilateralid_t quadrilateral_id,
-	ldraw::Diagonal splitType
-) -> std::optional<std::pair<ldraw::triangleid_t, ldraw::triangleid_t>>
-{
-	std::optional<std::pair<ldraw::triangleid_t, ldraw::triangleid_t>> result;
-	const auto resolved = editor.model().get2(quadrilateral_id);
-	if (resolved.object != nullptr)
-	{
-		const ldraw::Color color = resolved.object->colorIndex;
-		const std::array<geom::Triangle, 2> split = splitTriangles(splitType, resolved.object->points);
-		const int position = resolved.index.row();
-		editor.remove(position);
-		result = std::make_pair(
-			editor.insert<ldraw::Triangle>(position, split[0].points, color),
-			editor.insert<ldraw::Triangle>(position, split[1].points, color));
-	}
-	return result;
-}
-
 /**
  * @brief Modifies the !LDRAW_ORG line so that it becomes unofficial
  */
+/*
 void ldraw::makeUnofficial(ModelEditor& editor)
 {
 	if (editor.model().size() >= 4)
@@ -71,4 +44,24 @@
 			}
 		}
 	}
-}
\ No newline at end of file
+}
+*/
+
+ModelElement inverted(const ModelElement& element)
+{
+	return std::visit(overloaded{
+		[](Colored<SubfileReference> ref) -> ModelElement {
+			ref.inverted = not ref.inverted;
+			return ref;
+		},
+		[](Colored<Triangle> triangle) -> ModelElement {
+			std::swap(triangle.p1, triangle.p2);
+			return triangle;
+		},
+		[](Colored<Quadrilateral> quad) -> ModelElement {
+			std::swap(quad.p2, quad.p4);
+			return quad;
+		},
+		[](const ModelElement& x) { return x; }
+	}, element);
+}