Useful functions for making angle entering less error-prone.

Both functions convert the value to radians at compile time. For
example deg(180.0f) is converted to 3.14f. Less intuitive than
user-defined literals (C++11 feature), but works everywhere.

src/Magnum.h

@@ -41,6 +41,10 @@ typedef Math::Matrix3<GLfloat> Matrix3;
 /** @brief 4x4 floating-point matrix */
 typedef Math::Matrix4<GLfloat> Matrix4;
 
+/* Copying angle converters from Math namespace */
+using Math::deg;
+using Math::rad;
+
 }
 
 #endif

src/Math/Test/Matrix4Test.cpp

@@ -60,7 +60,7 @@ void Matrix4Test::rotation() {
         0.0f,       0.0f,       0.0f,       1.0f
     };
 
-    QVERIFY(Matrix4::rotation(-74*PI/180.0f, -1.0f, 2.0f, 2.0f) == Matrix4(matrix));
+    QVERIFY(Matrix4::rotation(deg(-74.0f), -1.0f, 2.0f, 2.0f) == Matrix4(matrix));
 }
 
 void Matrix4Test::debug() {

src/Math/Test/VectorTest.cpp

@@ -124,7 +124,7 @@ void VectorTest::angle() {
     float a[] = { 2.0f, 3.0f, 4.0f };
     float b[] = { 1.0f, -2.0f, 3.0f };
 
-    QCOMPARE(Vector3::angle(a, b), 1.16251f);
+    QCOMPARE(Vector3::angle(a, b), rad(1.16251f));
 }
 
 void VectorTest::negative() {

src/Math/constants.h

@@ -27,6 +27,21 @@ namespace Magnum { namespace Math {
 /** @brief Maximal tolerance when comparing floats */
 #define EPSILON 1.0e-6
 
+/**
+ * @brief Angle in degrees
+ *
+ * Function to make angle entering less error-prone. Converts the value to
+ * radians at compile time. For example @c deg(180.0f) is converted to @c 3.14f.
+ */
+template<class T> inline constexpr T deg(T value) { return value*PI/180; }
+
+/**
+ * @brief Angle in radians
+ *
+ * See also deg().
+ */
+template<class T> inline constexpr T rad(T value) { return value; }
+
 }}
 
 #endif

src/Test/CameraTest.cpp

@@ -40,7 +40,7 @@ void CameraTest::orthographic() {
 
 void CameraTest::perspective() {
     Camera camera;
-    camera.setPerspective(27*PI/180, 32.0f, 100);
+    camera.setPerspective(deg(27.0f), 32.0f, 100);
 
     GLfloat a[] = {
         4.1652994f, 0,          0,           0,