Ability to construct Matrix from rotation/scaling and translation parts.

src/Math/Matrix3.h

@@ -83,6 +83,23 @@ template<class T> class Matrix3: public Matrix<3, T> {
             );
         }
 
+        /**
+         * @brief Create matrix from rotation/scaling part and translation part
+         * @param rotationScaling   Rotation/scaling part (upper-left 2x2
+         *      matrix)
+         * @param translation       Translation part (first two elements of
+         *      third column)
+         *
+         * @see rotationScaling() const, translation() const
+         */
+        static Matrix3<T> from(const Matrix<2, T>& rotationScaling, const Vector2<T>& translation = Vector2<T>()) {
+            return from(
+                Vector3<T>(rotationScaling[0], T(0)),
+                Vector3<T>(rotationScaling[1], T(0)),
+                Vector3<T>(translation, T(1))
+            );
+        }
+
         /** @copydoc Matrix::Matrix(ZeroType) */
         inline constexpr explicit Matrix3(typename Matrix<3, T>::ZeroType): Matrix<3, T>(Matrix<3, T>::Zero) {}
 
@@ -107,7 +124,8 @@ template<class T> class Matrix3: public Matrix<3, T> {
          * @brief 2D rotation and scaling part of the matrix
          *
          * Upper-left 2x2 part of the matrix.
-         * @see rotation() const, rotation(T), Matrix4::rotationScaling() const
+         * @see from(const Matrix<2, T>&, const Vector2&), rotation() const,
+         *      rotation(T), Matrix4::rotationScaling() const
          */
         inline Matrix<2, T> rotationScaling() const {
             return Matrix<2, T>::from(

src/Math/Matrix4.h

@@ -173,6 +173,24 @@ template<class T> class Matrix4: public Matrix<4, T> {
             );
         }
 
+        /**
+         * @brief Create matrix from rotation/scaling part and translation part
+         * @param rotationScaling   Rotation/scaling part (upper-left 3x3
+         *      matrix)
+         * @param translation       Translation part (first three elements of
+         *      fourth column)
+         *
+         * @see rotationScaling() const, translation() const
+         */
+        static Matrix4<T> from(const Matrix<3, T>& rotationScaling, const Vector3<T>& translation = Vector3<T>()) {
+            return from(
+                Vector4<T>(rotationScaling[0], T(0)),
+                Vector4<T>(rotationScaling[1], T(0)),
+                Vector4<T>(rotationScaling[2], T(0)),
+                Vector4<T>(translation, T(1))
+            );
+        }
+
         /** @copydoc Matrix::Matrix(ZeroType) */
         inline constexpr explicit Matrix4(typename Matrix<4, T>::ZeroType): Matrix<4, T>(Matrix<4, T>::Zero) {}
 
@@ -198,8 +216,8 @@ template<class T> class Matrix4: public Matrix<4, T> {
          * @brief 3D rotation and scaling part of the matrix
          *
          * Upper-left 3x3 part of the matrix.
-         * @see rotation() const, rotation(T, const Vector3&),
-         *      Matrix3::rotationScaling() const
+         * @see from(const Matrix<3, T>&, const Vector3&), rotation() const,
+         *      rotation(T, const Vector3&), Matrix3::rotationScaling() const
          */
         inline Matrix<3, T> rotationScaling() const {
             /* Not Matrix3, because it is for affine 2D transformations */
@@ -224,7 +242,6 @@ template<class T> class Matrix4: public Matrix<4, T> {
                 (*this)[2].xyz().normalized());
         }
 
-
         /**
          * @brief Right-pointing 3D vector
          *

src/Math/Test/Matrix3Test.cpp

@@ -36,6 +36,7 @@ Matrix3Test::Matrix3Test() {
              &Matrix3Test::translation,
              &Matrix3Test::scaling,
              &Matrix3Test::rotation,
+             &Matrix3Test::fromParts,
              &Matrix3Test::rotationScalingPart,
              &Matrix3Test::rotationPart,
              &Matrix3Test::vectorParts,
@@ -95,6 +96,29 @@ void Matrix3Test::rotation() {
     CORRADE_COMPARE(Matrix3::rotation(deg(15.0f)), matrix);
 }
 
+void Matrix3Test::fromParts() {
+    Matrix2 rotationScaling(
+        3.0f, 5.0f,
+        4.0f, 4.0f
+    );
+
+    Vector2 translation(7.0f, -1.0f);
+
+    Matrix3 expected(
+        3.0f, 5.0f, 0.0f,
+        4.0f, 4.0f, 0.0f,
+        7.0f, -1.0f, 1.0f
+    );
+    CORRADE_COMPARE(Matrix3::from(rotationScaling, translation), expected);
+
+    Matrix3 expectedNoRotation(
+        3.0f, 5.0f, 0.0f,
+        4.0f, 4.0f, 0.0f,
+        0.0f, 0.0f, 1.0f
+    );
+    CORRADE_COMPARE(Matrix3::from(rotationScaling), expectedNoRotation);
+}
+
 void Matrix3Test::rotationScalingPart() {
     Matrix3 m(
         3.0f, 5.0f, 8.0f,

src/Math/Test/Matrix3Test.h

@@ -28,6 +28,7 @@ class Matrix3Test: public Corrade::TestSuite::Tester {
         void translation();
         void scaling();
         void rotation();
+        void fromParts();
         void rotationScalingPart();
         void rotationPart();
         void vectorParts();

src/Math/Test/Matrix4Test.cpp

@@ -39,6 +39,7 @@ Matrix4Test::Matrix4Test() {
              &Matrix4Test::rotationX,
              &Matrix4Test::rotationY,
              &Matrix4Test::rotationZ,
+             &Matrix4Test::fromParts,
              &Matrix4Test::rotationScalingPart,
              &Matrix4Test::rotationPart,
              &Matrix4Test::vectorParts,
@@ -135,6 +136,32 @@ void Matrix4Test::rotationZ() {
     CORRADE_COMPARE(Matrix4::rotationZ(rad(Math::Constants<float>::pi()/7)), matrix);
 }
 
+void Matrix4Test::fromParts() {
+    Matrix3 rotationScaling(
+        3.0f, 5.0f, 8.0f,
+        4.0f, 4.0f, 7.0f,
+        7.0f, -1.0f, 8.0f
+    );
+
+    Vector3 translation(9.0f, 4.0f, 5.0f);
+
+    Matrix4 expected(
+        3.0f, 5.0f, 8.0f, 0.0f,
+        4.0f, 4.0f, 7.0f, 0.0f,
+        7.0f, -1.0f, 8.0f, 0.0f,
+        9.0f, 4.0f, 5.0f, 1.0f
+    );
+    CORRADE_COMPARE(Matrix4::from(rotationScaling, translation), expected);
+
+    Matrix4 expectedNoTranslation(
+        3.0f, 5.0f, 8.0f, 0.0f,
+        4.0f, 4.0f, 7.0f, 0.0f,
+        7.0f, -1.0f, 8.0f, 0.0f,
+        0.0f, 0.0f, 0.0f, 1.0f
+    );
+    CORRADE_COMPARE(Matrix4::from(rotationScaling), expectedNoTranslation);
+}
+
 void Matrix4Test::rotationScalingPart() {
     Matrix4 m(
         3.0f, 5.0f, 8.0f, 4.0f,

src/Math/Test/Matrix4Test.h

@@ -31,6 +31,7 @@ class Matrix4Test: public Corrade::TestSuite::Tester {
         void rotationX();
         void rotationY();
         void rotationZ();
+        void fromParts();
         void rotationScalingPart();
         void rotationPart();
         void vectorParts();