feat: included geometry method

packages/geometry/lib/src/geometry.dart

@@ -105,3 +105,20 @@ num factorial(num n) {
     return n * factorial(n - 1);
   }
 }
+
+/// Arithmetic mean position of all the [Vector2]s in a figure.
+///
+/// For more information read: https://en.wikipedia.org/wiki/Centroid
+Vector2 centroid(List<Vector2> vertices) {
+  assert(
+    vertices.isNotEmpty,
+    'At least one vertex needed to calculate the centroid',
+  );
+
+  final centroid = Vector2.zero();
+  for (final vertex in vertices) {
+    centroid.add(vertex);
+  }
+
+  return centroid / vertices.length.toDouble();
+}

packages/geometry/test/src/geometry_test.dart

@@ -156,4 +156,41 @@ void main() {
       });
     });
   });
+
+  group('centroid', () {
+    test(
+      'throws AssertionError when vertices are empty',
+      () {
+        expect(() => centroid([]), throwsAssertionError);
+      },
+    );
+
+    test(
+      'is correct when one vertex is given',
+      () {
+        expect(centroid([Vector2.zero()]), Vector2.zero());
+      },
+    );
+
+    test(
+      'is correct when two vertex are given',
+      () {
+        expect(centroid([Vector2.zero(), Vector2(1, 1)]), Vector2(0.5, 0.5));
+      },
+    );
+
+    test(
+      'is correct when three vertex are given',
+      () {
+        expect(
+          centroid([
+            Vector2.zero(),
+            Vector2(1, 1),
+            Vector2(2, 2),
+          ]),
+          Vector2(1, 1),
+        );
+      },
+    );
+  });
 }