SceneGraph: fix aspect-ratio-corrected projection with inverted Y.

The test now passes again.

src/Magnum/SceneGraph/AbstractCamera.h

@@ -29,6 +29,7 @@
  * @brief Class @ref Magnum::SceneGraph::AbstractCamera, enum @ref Magnum::SceneGraph::AspectRatioPolicy, alias @ref Magnum::SceneGraph::AbstractBasicCamera2D, @ref Magnum::SceneGraph::AbstractBasicCamera3D, typedef @ref Magnum::SceneGraph::AbstractCamera2D, @ref Magnum::SceneGraph::AbstractCamera3D
  */
 
+#include "Magnum/Math/Functions.h"
 #include "Magnum/Math/Matrix3.h"
 #include "Magnum/Math/Matrix4.h"
 #include "Magnum/SceneGraph/AbstractFeature.h"
@@ -150,7 +151,7 @@ template<UnsignedInt dimensions, class T> class AbstractCamera: public AbstractF
 
         #ifndef DOXYGEN_GENERATING_OUTPUT
         void fixAspectRatio() {
-            _projectionMatrix = Implementation::aspectRatioFix<dimensions, T>(_aspectRatioPolicy, {rawProjectionMatrix[0].x(), rawProjectionMatrix[1].y()}, _viewport)*rawProjectionMatrix;
+            _projectionMatrix = Implementation::aspectRatioFix<dimensions, T>(_aspectRatioPolicy, {Math::abs(rawProjectionMatrix[0].x()), Math::abs(rawProjectionMatrix[1].y())}, _viewport)*rawProjectionMatrix;
         }
 
         MatrixTypeFor<dimensions, T> rawProjectionMatrix;

src/Magnum/SceneGraph/AbstractCamera.hpp

@@ -41,6 +41,7 @@ template<UnsignedInt dimensions, class T> MatrixTypeFor<dimensions, T> aspectRat
     if(projectionScale.x() == 0 || projectionScale.y() == 0 || viewport.x() == 0 || viewport.y() == 0 || aspectRatioPolicy == AspectRatioPolicy::NotPreserved)
         return {};
 
+    CORRADE_INTERNAL_ASSERT((projectionScale > Math::Vector2<T>(0)).all() && (viewport > Vector2i(0)).all());
     Math::Vector2<T> relativeAspectRatio = Math::Vector2<T>(viewport)*projectionScale;
 
     /* Extend on larger side = scale larger side down