diff -r e1ced2523cad -r b6cbba6e29a1 src/polygoncache.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/polygoncache.cpp	Thu Mar 03 11:42:52 2022 +0200
@@ -0,0 +1,51 @@
+#include "polygoncache.h"
+#include "documentmanager.h"
+
+PolygonCache::PolygonCache(Model *model) :
+	model{model}
+{
+	const auto mark = [this](){ this->needRecache = true; };
+	connect(model, &Model::dataChanged, mark);
+	connect(model, &Model::objectAdded, mark);
+	connect(model, &Model::objectRemoved, mark);
+}
+
+/**
+ * @brief Gets a list of GL polygons that are used to represent this model.
+ * @details Will build polygons if polygons are outdated.
+ * @param documents Documents to use to resolve subfile references
+ * @return vector of GL polygons
+ */
+std::vector<gl::Polygon> PolygonCache::getPolygons(DocumentManager* documents)
+{
+	if (this->needRecache)
+	{
+		this->cachedPolygons.clear();
+		const std::optional<ModelId> modelId = documents->findIdForModel(this->model);
+		if (modelId.has_value())
+		{
+			ldraw::GetPolygonsContext context{modelId.value(), documents};
+			for (int i = 0; i < this->model->size(); i += 1)
+			{
+				this->getObjectPolygons(i, this->cachedPolygons, &context);
+			}
+		}
+		this->needRecache = false;
+	}
+	return this->cachedPolygons;
+}
+
+/**
+ * @brief Gets the GL polygons of the object at the specified position in the model
+ * @param index Index of object in the model
+ * @param polygons_out Vector to add polygons into
+ * @param context Context to use to resolve subfile references
+ */
+void PolygonCache::getObjectPolygons(
+	const int index,
+	std::vector<gl::Polygon>& polygons_out,
+	ldraw::GetPolygonsContext* context) const
+{
+	const ldraw::Object* object = (*this->model)[unsigned_cast(index)];
+	object->getPolygons(polygons_out, context);
+}