Math: conversion constructor for Frustum.

src/Magnum/Math/Frustum.h

@@ -72,6 +72,14 @@ template<class T> class Frustum {
         /** @brief Construct a frustum from plane equations */
         constexpr /*implicit*/ Frustum(const Vector4<T>& left, const Vector4<T>& right, const Vector4<T>& bottom, const Vector4<T>& top, const Vector4<T>& near, const Vector4<T>& far) noexcept: _data{left, right, bottom, top, near, far} {}
 
+        /**
+         * @brief Construct frustum from another of different type
+         *
+         * Performs only default casting on the values, no rounding or
+         * anything else.
+         */
+        template<class U> constexpr explicit Frustum(const Frustum<U>& other) noexcept;
+
         /** @brief Equality comparison */
         bool operator==(const Frustum<T>& other) const {
             for(std::size_t i = 0; i != 6; ++i)
@@ -150,6 +158,14 @@ template<class T> constexpr Frustum<T>::Frustum(IdentityInitT) noexcept: _data{
     { 0.0f,  0.0f,  1.0f, 1.0f},
     { 0.0f,  0.0f, -1.0f, 1.0f}} {}
 
+template<class T> template<class U> constexpr Frustum<T>::Frustum(const Frustum<U>& other) noexcept: _data{
+    Vector4<T>{other[0]},
+    Vector4<T>{other[1]},
+    Vector4<T>{other[2]},
+    Vector4<T>{other[3]},
+    Vector4<T>{other[4]},
+    Vector4<T>{other[5]}} {}
+
 }}
 
 #endif

src/Magnum/Math/Test/FrustumTest.cpp

@@ -38,6 +38,7 @@ struct FrustumTest: Corrade::TestSuite::Tester {
     void construct();
     void constructIdentity();
     void constructNoInit();
+    void constructConversion();
     void constructCopy();
     void constructFromMatrix();
 
@@ -51,11 +52,13 @@ struct FrustumTest: Corrade::TestSuite::Tester {
 typedef Math::Vector4<Float> Vector4;
 typedef Math::Matrix4<Float> Matrix4;
 typedef Math::Frustum<Float> Frustum;
+typedef Math::Frustum<Double> Frustumd;
 
 FrustumTest::FrustumTest() {
     addTests({&FrustumTest::construct,
               &FrustumTest::constructIdentity,
               &FrustumTest::constructNoInit,
+              &FrustumTest::constructConversion,
               &FrustumTest::constructCopy,
               &FrustumTest::constructFromMatrix,
 
@@ -132,6 +135,31 @@ void FrustumTest::constructNoInit() {
     CORRADE_VERIFY((std::is_nothrow_constructible<Frustum, NoInitT>::value));
 }
 
+void FrustumTest::constructConversion() {
+    constexpr Frustumd a{
+        {-1.0,  2.0, -3.0, 0.1},
+        { 1.0, -2.0,  3.0, 0.2},
+        {-4.0,  5.0, -6.0, 0.3},
+        { 4.0, -5.0,  6.0, 0.4},
+        {-7.0,  8.0, -9.0, 0.5},
+        { 7.0,  8.0,  9.0, 0.6}};
+    Frustum expected{
+        {-1.0f,  2.0f, -3.0f, 0.1f},
+        { 1.0f, -2.0f,  3.0f, 0.2f},
+        {-4.0f,  5.0f, -6.0f, 0.3f},
+        { 4.0f, -5.0f,  6.0f, 0.4f},
+        {-7.0f,  8.0f, -9.0f, 0.5f},
+        { 7.0f,  8.0f,  9.0f, 0.6f}};
+
+    constexpr Frustum b{a};
+    CORRADE_COMPARE(b, expected);
+
+    /* Implicit conversion is not allowed */
+    CORRADE_VERIFY(!(std::is_convertible<Frustum, Frustumd>::value));
+
+    CORRADE_VERIFY((std::is_nothrow_constructible<Frustum, Frustumd>::value));
+}
+
 void FrustumTest::constructCopy() {
     constexpr Frustum a{
         {-1.0f,  2.0f, -3.0f, 0.1f},