diff -r 000781318c36 -r b54b350dff5d src/geometry.cpp
--- a/src/geometry.cpp	Fri Jul 30 01:28:39 2021 +0300
+++ b/src/geometry.cpp	Fri Aug 27 00:55:32 2021 +0300
@@ -1,5 +1,7 @@
 #include <glm/gtc/matrix_transform.hpp>
 #include "geometry.h"
+#include "ring.h"
+#include "maths.h"
 
 /**
  * @brief Computes line-plane intersection
@@ -196,3 +198,24 @@
 		glm::vec2{rectangle.right(), rectangle.bottom()}
 	};
 }
+
+bool geom::convex(const std::vector<glm::vec3>& polygon)
+{
+	const int n = polygon.size();
+	auto polygonRing = iter::ring(polygon, n);
+	std::vector<glm::vec3> crosses;
+	crosses.resize(n);
+	for (int i = 0; i < n; i += 1)
+	{
+		crosses[i] = glm::cross(polygonRing[i - 1] - polygonRing[i], polygonRing[i + 1] - polygonRing[i]);
+	}
+	for (int i = 0; i < n - 1; i += 1)
+	{
+		const float dotp = glm::dot(crosses[0], crosses[i + 1]);
+		if (dotp < 0 or qFuzzyIsNull(dotp))
+		{
+			return false;
+		}
+	}
+	return true;
+}