Function for getting rotation part of Matrix4.

src/Math/Matrix4.h

@@ -158,6 +158,14 @@ template<class T> class Matrix4: public Matrix<T, 4> {
 
         /** @copydoc Matrix::inversed() */
         inline Matrix4<T> inversed() const { return Matrix<T, 4>::inversed(); }
+
+        /** @brief Rotation part of the matrix */
+        inline Matrix3<T> rotation() const {
+            return Matrix3<T>::from(
+                (*this)[0].xyz().normalized(),
+                (*this)[1].xyz().normalized(),
+                (*this)[2].xyz().normalized());
+        }
 };
 
 #ifndef DOXYGEN_GENERATING_OUTPUT

src/Math/Test/Matrix4Test.cpp

@@ -29,6 +29,7 @@ using namespace Corrade::Utility;
 namespace Magnum { namespace Math { namespace Test {
 
 typedef Math::Matrix4<float> Matrix4;
+typedef Math::Matrix3<float> Matrix3;
 
 void Matrix4Test::translation() {
     Matrix4 matrix(
@@ -63,6 +64,20 @@ void Matrix4Test::rotation() {
     QVERIFY(Matrix4::rotation(deg(-74.0f), {-1.0f, 2.0f, 2.0f}) == matrix);
 }
 
+void Matrix4Test::rotationPart() {
+    Matrix3 expectedRotationPart(
+        0.35612214f,  -0.80181062f, 0.47987163f,
+        0.47987163f,  0.59757638f,  0.6423595f,
+        -0.80181062f, 0.0015183985f, 0.59757638f
+    );
+
+    Matrix4 rotation = Matrix4::rotation(deg(-74.0f), {-1.0f, 2.0f, 2.0f});
+    QVERIFY(rotation.rotation() == expectedRotationPart);
+
+    Matrix4 rotationTransformed = Matrix4::translation({2.0f, 5.0f, -3.0f})*rotation*Matrix4::scaling(Vector3<float>(9.0f));
+    QVERIFY(rotationTransformed.rotation() == expectedRotationPart);
+}
+
 void Matrix4Test::debug() {
     Matrix4 m(
         3.0f, 5.0f, 8.0f, 4.0f,

src/Math/Test/Matrix4Test.h

@@ -26,6 +26,7 @@ class Matrix4Test: public QObject {
         void translation();
         void scaling();
         void rotation();
+        void rotationPart();
 
         void debug();
 };