DebugTools: simplified also 2D ForceRenderer transformation computation.

Also removed unneeded tests, as they don't reflect the code in any way.

src/DebugTools/Implementation/ForceRendererTransformation.h

@@ -35,7 +35,7 @@ namespace Magnum { namespace DebugTools { namespace Implementation {
 template<UnsignedInt dimensions> typename DimensionTraits<dimensions, Float>::MatrixType forceRendererTransformation(const typename DimensionTraits<dimensions, Float>::VectorType& forcePosition, const typename DimensionTraits<dimensions, Float>::VectorType& force);
 
 template<> inline Matrix3 forceRendererTransformation<2>(const Vector2& forcePosition, const Vector2& force) {
-    return Matrix3::from({force, Vector2(-force.y(), force.x())}, forcePosition);
+    return Matrix3::from({force, force.perpendicular()}, forcePosition);
 }
 
 template<> Matrix4 forceRendererTransformation<3>(const Vector3& forcePosition, const Vector3& force) {

src/DebugTools/Test/ForceRendererTest.cpp

@@ -33,9 +33,7 @@ class ForceRendererTest: public TestSuite::Tester {
         explicit ForceRendererTest();
 
         void zero2D();
-        void parallel2D();
-        void antiParallel2D();
-        void arbitrary2D();
+        void common2D();
 
         void zero3D();
         void parallel3D();
@@ -45,9 +43,7 @@ class ForceRendererTest: public TestSuite::Tester {
 
 ForceRendererTest::ForceRendererTest() {
     addTests({&ForceRendererTest::zero2D,
-              &ForceRendererTest::parallel2D,
-              &ForceRendererTest::antiParallel2D,
-              &ForceRendererTest::arbitrary2D,
+              &ForceRendererTest::common2D,
 
               &ForceRendererTest::zero3D,
               &ForceRendererTest::parallel3D,
@@ -60,17 +56,7 @@ void ForceRendererTest::zero2D() {
                     Matrix3::translation({0.5f, -3.0f})*Matrix3::scaling(Vector2(0.0f)));
 }
 
-void ForceRendererTest::parallel2D() {
-    CORRADE_COMPARE(Implementation::forceRendererTransformation<2>({0.5f, -3.0f}, Vector2::xAxis(2.5f)),
-                    Matrix3::translation({0.5f, -3.0f})*Matrix3::scaling(Vector2(2.5f)));
-}
-
-void ForceRendererTest::antiParallel2D() {
-    CORRADE_COMPARE(Implementation::forceRendererTransformation<2>({0.5f, -3.0f}, Vector2::xAxis(-2.5f)),
-                    Matrix3::translation({0.5f, -3.0f})*Matrix3::scaling(Vector2(-2.5f)));
-}
-
-void ForceRendererTest::arbitrary2D() {
+void ForceRendererTest::common2D() {
     Vector2 force(2.7f, -11.5f);
     Matrix3 m = Implementation::forceRendererTransformation<2>({0.5f, -3.0f}, force);