Math: whoops, forgot about StrictWeakOrdering for Frustum.

Just a stretched version of the test for Matrix4. Hope that's okay.

src/Magnum/Math/Frustum.h

@@ -181,6 +181,24 @@ template<class T> template<class U> constexpr Frustum<T>::Frustum(const Frustum<
     Vector4<T>{other[4]},
     Vector4<T>{other[5]}} {}
 
+namespace Implementation {
+
+template<class T> struct StrictWeakOrdering<Frustum<T>> {
+    bool operator()(const Frustum<T>& a, const Frustum<T>& b) const {
+        StrictWeakOrdering<Vector<4, T>> o;
+        for(std::size_t i = 0; i < 6; ++i) {
+            if(o(a[i], b[i]))
+                return true;
+            if(o(b[i], a[i]))
+                return false;
+        }
+
+        return false; /* a and b are equivalent */
+    }
+};
+
+}
+
 }}
 
 #endif

src/Magnum/Math/Test/FrustumTest.cpp

@@ -29,6 +29,7 @@
 #include <Corrade/TestSuite/Compare/Container.h>
 
 #include "Magnum/Math/Frustum.h"
+#include "Magnum/Math/StrictWeakOrdering.h"
 
 struct Frstm {
     float data[24];
@@ -77,6 +78,8 @@ struct FrustumTest: Corrade::TestSuite::Tester {
 
     void compare();
 
+    void strictWeakOrdering();
+
     void debug();
 };
 
@@ -98,6 +101,8 @@ FrustumTest::FrustumTest() {
 
               &FrustumTest::compare,
 
+              &FrustumTest::strictWeakOrdering,
+
               &FrustumTest::debug});
 }
 
@@ -310,6 +315,40 @@ void FrustumTest::compare() {
     CORRADE_VERIFY(a != c);
 }
 
+void FrustumTest::strictWeakOrdering() {
+    StrictWeakOrdering o;
+    const Frustum a{
+        {1.0f, 1.0f, 2.0f, 2.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {3.0f, 1.0f, 2.0f, 4.0f}};
+    const Frustum b{
+        {2.0f, 1.0f, 2.0f, 3.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {4.0f, 1.0f, 2.0f, 5.0f}};
+    const Frustum c{
+        {1.0f, 1.0f, 2.0f, 2.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {5.0f, 5.0f, 6.0f, 5.0f},
+        {3.0f, 1.0f, 2.0f, 5.0f}};
+
+    CORRADE_VERIFY( o(a, b));
+    CORRADE_VERIFY(!o(b, a));
+    CORRADE_VERIFY( o(a, c));
+    CORRADE_VERIFY(!o(c, a));
+    CORRADE_VERIFY( o(c, b));
+    CORRADE_VERIFY(!o(b, c));
+
+    CORRADE_VERIFY(!o(a, a));
+}
+
 void FrustumTest::debug() {
     Frustum frustum{
         {-1.0f,  2.0f, -3.0f, 0.1f},