LibGfx: Add Matrix3x3

This defines `Matrix3x3`, `FloatMatrix3x3` and `DoubleMatrix3x3`
mirroring `Matrix4x4`. Since we will need matrix multiplication with a
`Vector3` for LibGL's normalization, we also add that `*` operator.

Userland/Libraries/LibGfx/Matrix3x3.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2021, Jelle Raaijmakers <jelle@gmta.nl>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGfx/Matrix.h>
+#include <LibGfx/Vector3.h>
+
+namespace Gfx {
+
+template<typename T>
+using Matrix3x3 = Matrix<3, T>;
+
+template<typename T>
+constexpr static Vector3<T> operator*(Matrix3x3<T> const& m, Vector3<T> const& v)
+{
+    auto const& elements = m.elements();
+    return Vector3<T>(
+        v.x() * elements[0][0] + v.y() * elements[0][1] + v.z() * elements[0][2],
+        v.x() * elements[1][0] + v.y() * elements[1][1] + v.z() * elements[1][2],
+        v.x() * elements[2][0] + v.y() * elements[2][1] + v.z() * elements[2][2]);
+}
+
+typedef Matrix3x3<float> FloatMatrix3x3;
+typedef Matrix3x3<double> DoubleMatrix3x3;
+}
+
+using Gfx::DoubleMatrix3x3;
+using Gfx::FloatMatrix3x3;
+using Gfx::Matrix3x3;