Math: assert uniform scaling in Matrix[34]::rotation().

Needed to adjust the test cases slightly, because they were firing the
assert even if they shouldn't and the "expect fail" case wasn't working
at all. I now badly need proper floating-point equality comparison.

src/Math/Matrix3.h

@@ -191,12 +191,14 @@ template<class T> class Matrix3: public Matrix<3, T> {
         /**
          * @brief 2D rotation part of the matrix
          *
-         * Normalized upper-left 2x2 part of the matrix.
+         * Normalized upper-left 2x2 part of the matrix. Expects uniform
+         * scaling.
          * @see rotationNormalized(), rotationScaling(), @ref uniformScaling(),
          *      rotation(T), Matrix4::rotation() const
-         * @todo assert uniform scaling (otherwise this would be garbage)
          */
         Matrix<2, T> rotation() const {
+            CORRADE_ASSERT(TypeTraits<T>::equals((*this)[0].xy().dot(), (*this)[1].xy().dot()),
+                           "Math::Matrix3::rotation(): the matrix doesn't have uniform scaling", {});
             return {(*this)[0].xy().normalized(),
                     (*this)[1].xy().normalized()};
         }

src/Math/Matrix4.h

@@ -258,11 +258,11 @@ template<class T> class Matrix4: public Matrix<4, T> {
         /**
          * @brief 3D rotation part of the matrix
          *
-         * Normalized upper-left 3x3 part of the matrix.
+         * Normalized upper-left 3x3 part of the matrix. Expects uniform
+         * scaling.
          * @see rotationNormalized(), rotationScaling() const,
          *      @ref uniformScaling(), rotation(T, const Vector3&),
          *      Matrix3::rotation() const
-         * @todo assert uniform scaling (otherwise this would be garbage)
          */
         /* Not Matrix3, because it is for affine 2D transformations */
         Matrix<3, T> rotation() const;
@@ -452,6 +452,9 @@ template<class T> Matrix4<T> Matrix4<T>::perspectiveProjection(const Vector2<T>&
 }
 
 template<class T> inline Matrix<3, T> Matrix4<T>::rotation() const {
+    CORRADE_ASSERT(TypeTraits<T>::equals((*this)[0].xyz().dot(), (*this)[1].xyz().dot()) &&
+                   TypeTraits<T>::equals((*this)[1].xyz().dot(), (*this)[2].xyz().dot()),
+        "Math::Matrix4::rotation(): the matrix doesn't have uniform scaling", {});
     return {(*this)[0].xyz().normalized(),
             (*this)[1].xyz().normalized(),
             (*this)[2].xyz().normalized()};

src/Math/Test/Matrix3Test.cpp

@@ -319,21 +319,18 @@ void Matrix3Test::rotationPart() {
     CORRADE_COMPARE(rotationTranslationPart, expectedRotationPart);
 
     /* Test uniform scaling */
-    Matrix3 rotationScaling = rotation*Matrix3::scaling(Vector2(9.0f));
+    Matrix3 rotationScaling = rotation*Matrix3::scaling(Vector2(3.0f));
     Matrix2 rotationScalingPart = rotationScaling.rotation();
     CORRADE_COMPARE(rotationScalingPart.determinant(), 1.0f);
     CORRADE_COMPARE(rotationScalingPart*rotationScalingPart.transposed(), Matrix2());
     CORRADE_COMPARE(rotationScalingPart, expectedRotationPart);
 
     /* Fails on non-uniform scaling */
-    {
-        CORRADE_EXPECT_FAIL("Assertion on uniform scaling is not implemented yet.");
-        std::ostringstream o;
-        Error::setOutput(&o);
-        Matrix3 rotationScaling2 = rotation*Matrix3::scaling(Vector2::yScale(3.5f));
-        CORRADE_COMPARE(o.str(), "Math::Matrix3::rotation(): the matrix doesn't have uniform scaling\n");
-        CORRADE_COMPARE(rotationScaling2, Matrix3(Matrix3::Zero));
-    }
+    std::ostringstream o;
+    Error::setOutput(&o);
+    Matrix2 rotationScaling2 = (rotation*Matrix3::scaling(Vector2::yScale(3.5f))).rotation();
+    CORRADE_COMPARE(o.str(), "Math::Matrix3::rotation(): the matrix doesn't have uniform scaling\n");
+    CORRADE_COMPARE(rotationScaling2, Matrix2());
 }
 
 void Matrix3Test::uniformScalingPart() {

src/Math/Test/Matrix4Test.cpp

@@ -405,21 +405,18 @@ void Matrix4Test::rotationPart() {
     CORRADE_COMPARE(rotationTranslationPart, expectedRotationPart);
 
     /* Test uniform scaling */
-    Matrix4 rotationScaling = rotation*Matrix4::scaling(Vector3(9.0f));
+    Matrix4 rotationScaling = rotation*Matrix4::scaling(Vector3(3.0f));
     Matrix3 rotationScalingPart = rotationScaling.rotation();
     CORRADE_COMPARE(rotationScalingPart.determinant(), 1.0f);
     CORRADE_COMPARE(rotationScalingPart*rotationScalingPart.transposed(), Matrix3());
     CORRADE_COMPARE(rotationScalingPart, expectedRotationPart);
 
     /* Fails on non-uniform scaling */
-    {
-        CORRADE_EXPECT_FAIL("Assertion on uniform scaling is not implemented yet.");
-        std::ostringstream o;
-        Error::setOutput(&o);
-        Matrix4 rotationScaling2 = rotation*Matrix4::scaling(Vector3::yScale(3.5f));
-        CORRADE_COMPARE(o.str(), "Math::Matrix4::rotation(): the matrix doesn't have uniform scaling\n");
-        CORRADE_COMPARE(rotationScaling2, Matrix4(Matrix4::Zero));
-    }
+    std::ostringstream o;
+    Error::setOutput(&o);
+    Matrix3 rotationScaling2 = (rotation*Matrix4::scaling(Vector3::yScale(3.5f))).rotation();
+    CORRADE_COMPARE(o.str(), "Math::Matrix4::rotation(): the matrix doesn't have uniform scaling\n");
+    CORRADE_COMPARE(rotationScaling2, Matrix3());
 }
 
 void Matrix4Test::uniformScalingPart() {