Faster alternatives for rotation around main axes.

src/Math/Matrix4.h

@@ -73,6 +73,8 @@ template<class T> class Matrix4: public Matrix<4, T> {
          * @param angle Rotation angle (counterclockwise, in radians)
          * @param vec   Normalized rotation axis
          *
+         * If possible, use faster alternatives like xRotation(), yRotation()
+         * or zRotation().
          * @see rotation() const, Matrix3::rotation(T), Vector3::xAxis(),
          *      Vector3::yAxis(), Vector3::zAxis(), deg(), rad()
          * @attention Assertion fails on non-normalized rotation vector and
@@ -110,6 +112,66 @@ template<class T> class Matrix4: public Matrix<4, T> {
             );
         }
 
+        /**
+         * @brief 3D rotation around X axis
+         * @param angle Rotation angle (counterclockwise, in radians)
+         *
+         * Faster than calling `Matrix4::rotation(angle, Vector3::xAxis())`.
+         * @see rotation(T, const Vector3&), yRotation(), zRotation(),
+         *      rotation() const, Matrix3::rotation(T), deg(), rad()
+         */
+        static Matrix4<T> xRotation(T angle) {
+            T sine = std::sin(angle);
+            T cosine = std::cos(angle);
+
+            return Matrix4<T>( /* Column-major! */
+                T(1), T(0), T(0), T(0),
+                T(0), cosine, sine, T(0),
+                T(0), -sine, cosine, T(0),
+                T(0), T(0), T(0), T(1)
+            );
+        }
+
+        /**
+         * @brief 3D rotation around Y axis
+         * @param angle Rotation angle (counterclockwise, in radians)
+         *
+         * Faster than calling `Matrix4::rotation(angle, Vector3::yAxis())`.
+         * @see rotation(T, const Vector3&), xRotation(), zRotation(),
+         *      rotation() const, Matrix3::rotation(T), deg(), rad()
+         */
+        static Matrix4<T> yRotation(T angle) {
+            T sine = std::sin(angle);
+            T cosine = std::cos(angle);
+
+            return Matrix4<T>( /* Column-major! */
+                cosine, T(0), -sine, T(0),
+                T(0), T(1), T(0), T(0),
+                sine, T(0), cosine, T(0),
+                T(0), T(0), T(0), T(1)
+            );
+        }
+
+        /**
+         * @brief 3D rotation matrix around Z axis
+         * @param angle Rotation angle (counterclockwise, in radians)
+         *
+         * Faster than calling `Matrix4::rotation(angle, Vector3::zAxis())`.
+         * @see rotation(T, const Vector3&), xRotation(), yRotation(),
+         *      rotation() const, Matrix3::rotation(T), deg(), rad()
+         */
+        static Matrix4<T> zRotation(T angle) {
+            T sine = std::sin(angle);
+            T cosine = std::cos(angle);
+
+            return Matrix4<T>( /* Column-major! */
+                cosine, sine, T(0), T(0),
+                -sine, cosine, T(0), T(0),
+                T(0), T(0), T(1), T(0),
+                T(0), T(0), T(0), T(1)
+            );
+        }
+
         /** @copydoc Matrix::Matrix(ZeroType) */
         inline constexpr explicit Matrix4(typename Matrix<4, T>::ZeroType): Matrix<4, T>(Matrix<4, T>::Zero) {}
 

src/Math/Test/Matrix4Test.cpp

@@ -36,6 +36,9 @@ Matrix4Test::Matrix4Test() {
              &Matrix4Test::translation,
              &Matrix4Test::scaling,
              &Matrix4Test::rotation,
+             &Matrix4Test::xRotation,
+             &Matrix4Test::yRotation,
+             &Matrix4Test::zRotation,
              &Matrix4Test::rotationScalingPart,
              &Matrix4Test::rotationPart,
              &Matrix4Test::translationPart,
@@ -105,6 +108,33 @@ void Matrix4Test::rotation() {
     CORRADE_COMPARE(Matrix4::rotation(deg(-74.0f), Vector3(-1.0f, 2.0f, 2.0f).normalized()), matrix);
 }
 
+void Matrix4Test::xRotation() {
+    Matrix4 matrix(1.0f,  0.0f,        0.0f,        0.0f,
+                   0.0f,  0.90096887f, 0.43388374f, 0.0f,
+                   0.0f, -0.43388374f, 0.90096887f, 0.0f,
+                   0.0f,  0.0f,        0.0f,        1.0f);
+    CORRADE_COMPARE(Matrix4::rotation(rad(Math::Constants<float>::pi()/7), Vector3::xAxis()), matrix);
+    CORRADE_COMPARE(Matrix4::xRotation(rad(Math::Constants<float>::pi()/7)), matrix);
+}
+
+void Matrix4Test::yRotation() {
+    Matrix4 matrix(0.90096887f, 0.0f, -0.43388374f, 0.0f,
+                   0.0f,        1.0f,  0.0f,        0.0f,
+                   0.43388374f, 0.0f,  0.90096887f, 0.0f,
+                   0.0f,        0.0f,  0.0f,        1.0f);
+    CORRADE_COMPARE(Matrix4::rotation(rad(Math::Constants<float>::pi()/7), Vector3::yAxis()), matrix);
+    CORRADE_COMPARE(Matrix4::yRotation(rad(Math::Constants<float>::pi()/7)), matrix);
+}
+
+void Matrix4Test::zRotation() {
+    Matrix4 matrix( 0.90096887f, 0.43388374f, 0.0f, 0.0f,
+                   -0.43388374f, 0.90096887f, 0.0f, 0.0f,
+                    0.0f,        0.0f,        1.0f, 0.0f,
+                    0.0f,        0.0f,        0.0f, 1.0f);
+    CORRADE_COMPARE(Matrix4::rotation(rad(Math::Constants<float>::pi()/7), Vector3::zAxis()), matrix);
+    CORRADE_COMPARE(Matrix4::zRotation(rad(Math::Constants<float>::pi()/7)), matrix);
+}
+
 void Matrix4Test::rotationScalingPart() {
     Matrix4 m(
         3.0f, 5.0f, 8.0f, 4.0f,

src/Math/Test/Matrix4Test.h

@@ -28,6 +28,9 @@ class Matrix4Test: public Corrade::TestSuite::Tester<Matrix4Test> {
         void translation();
         void scaling();
         void rotation();
+        void xRotation();
+        void yRotation();
+        void zRotation();
         void rotationScalingPart();
         void rotationPart();
         void translationPart();