diff -r 38f6fad61bad -r bc92f97498f7 src/geometry.cpp
--- a/src/geometry.cpp	Tue Jun 28 19:31:55 2022 +0300
+++ b/src/geometry.cpp	Tue Jun 28 19:35:09 2022 +0300
@@ -1,7 +1,6 @@
 #include <glm/gtc/matrix_transform.hpp>
 #include "src/geometry.h"
 #include "src/basics.h"
-#include "src/ring.h"
 
 /**
  * @brief Computes line-plane intersection
@@ -218,12 +217,14 @@
 bool isConvex(const std::vector<glm::vec3>& polygon)
 {
 	const std::size_t n = polygon.size();
-	auto polygonRing = iter::ring(polygon, n);
 	std::vector<glm::vec3> crosses;
 	crosses.resize(n);
 	for (std::size_t i = 0; i < n; i += 1)
 	{
-		crosses[i] = glm::cross(polygonRing[i - 1] - polygonRing[i], polygonRing[i + 1] - polygonRing[i]);
+		const glm::vec3 v1 = polygon[(i + n - 1) % n];
+		const glm::vec3 v2 = polygon[i];
+		const glm::vec3 v3 = polygon[(i + 1) % n];
+		crosses[i] = glm::cross(v1 - v2, v3 - v2);
 	}
 	return not std::any_of(
 		crosses.begin() + 1,