From 10dd468ecaa8a229077d57adea5fdcbc4e5487f8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20Vondru=C5=A1?= <mosra@centrum.cz>
Date: Sat, 22 Feb 2020 22:53:40 +0100
Subject: [PATCH] Math: minimal support for Half in TypeTraits.

---
 src/Magnum/Math/Test/TypeTraitsTest.cpp | 19 ++++++++++++++++++-
 src/Magnum/Math/TypeTraits.h            | 24 ++++++++++++++++--------
 2 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/src/Magnum/Math/Test/TypeTraitsTest.cpp b/src/Magnum/Math/Test/TypeTraitsTest.cpp
index b9b64ba94..41cb71115 100644
--- a/src/Magnum/Math/Test/TypeTraitsTest.cpp
+++ b/src/Magnum/Math/Test/TypeTraitsTest.cpp
@@ -27,6 +27,7 @@
 #include <Corrade/TestSuite/Tester.h>
 #include <Corrade/Utility/DebugStl.h>
 
+#include "Magnum/Math/Half.h"
 #include "Magnum/Math/Math.h"
 #include "Magnum/Math/TypeTraits.h"
 #include "Magnum/Math/Constants.h"
@@ -48,6 +49,7 @@ struct TypeTraitsTest: Corrade::TestSuite::Tester {
     void underlyingTypeOf();
 
     template<class T> void equalsIntegral();
+    void equalsHalf();
     template<class T> void equalsFloatingPoint0();
     template<class T> void equalsFloatingPoint1();
     template<class T> void equalsFloatingPointLarge();
@@ -125,6 +127,8 @@ TypeTraitsTest::TypeTraitsTest() {
               &TypeTraitsTest::equalsIntegral<Long>,
               #endif
 
+              &TypeTraitsTest::equalsHalf,
+
               &TypeTraitsTest::equalsFloatingPoint0<Float>,
               &TypeTraitsTest::equalsFloatingPoint0<Double>,
               #ifndef CORRADE_TARGET_EMSCRIPTEN
@@ -191,9 +195,11 @@ void TypeTraitsTest::isScalar() {
     CORRADE_VERIFY(IsScalar<char>::value);
     CORRADE_VERIFY(IsScalar<UnsignedShort>::value);
     CORRADE_VERIFY(IsScalar<Deg<Float>>::value);
+    CORRADE_VERIFY(IsScalar<Half>::value);
     CORRADE_VERIFY((IsScalar<Unit<Rad, Double>>::value));
     CORRADE_VERIFY(!IsScalar<Vector2<Float>>::value);
     CORRADE_VERIFY(!IsVector<Matrix2x3<Float>>::value);
+    CORRADE_VERIFY(!IsScalar<Color3<Half>>::value);
     CORRADE_VERIFY(!IsScalar<char*>::value);
     CORRADE_VERIFY(!IsScalar<bool>::value);
 }
@@ -203,6 +209,7 @@ void TypeTraitsTest::isVector() {
     CORRADE_VERIFY(!IsVector<Deg<UnsignedByte>>::value);
     CORRADE_VERIFY((IsVector<Vector<2, Deg<Float>>>::value));
     CORRADE_VERIFY(IsVector<Color3<UnsignedByte>>::value);
+    CORRADE_VERIFY(IsVector<Color3<Half>>::value);
     CORRADE_VERIFY(!IsVector<Matrix2x3<Float>>::value);
     CORRADE_VERIFY(!IsVector<char*>::value);
 }
@@ -218,6 +225,7 @@ void TypeTraitsTest::isIntegral() {
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     CORRADE_VERIFY(IsIntegral<Vector2<Long>>::value);
     #endif
+    CORRADE_VERIFY(!IsIntegral<Half>::value);
     CORRADE_VERIFY(!IsIntegral<Deg<Float>>::value);
     CORRADE_VERIFY(!IsIntegral<char*>::value);
     CORRADE_VERIFY(!IsIntegral<bool>::value);
@@ -232,13 +240,15 @@ void TypeTraitsTest::isFloatingPoint() {
     CORRADE_VERIFY(IsFloatingPoint<Vector2<long double>>::value);
     #endif
     CORRADE_VERIFY(IsFloatingPoint<Deg<Float>>::value);
+    CORRADE_VERIFY(IsFloatingPoint<Color4<Half>>::value);
     CORRADE_VERIFY((IsFloatingPoint<Unit<Rad, Float>>::value));
-    CORRADE_VERIFY(!IsFloatingPoint<Deg<Half>>::value);
+    CORRADE_VERIFY(IsFloatingPoint<Deg<Half>>::value);
     CORRADE_VERIFY(!IsFloatingPoint<char*>::value);
 }
 
 void TypeTraitsTest::isUnitless() {
     CORRADE_VERIFY(IsUnitless<Int>::value);
+    CORRADE_VERIFY(IsUnitless<Half>::value);
     CORRADE_VERIFY(IsUnitless<Color4<Float>>::value);
     CORRADE_VERIFY(!IsUnitless<Deg<Float>>::value);
     CORRADE_VERIFY(!(IsUnitless<Unit<Rad, Double>>::value));
@@ -266,6 +276,13 @@ template<class T> void TypeTraitsTest::equalsIntegral() {
     CORRADE_VERIFY(!TypeTraits<T>::equals(T(1), T(1)+TypeTraits<T>::epsilon()));
 }
 
+void TypeTraitsTest::equalsHalf() {
+    CORRADE_VERIFY(TypeTraits<Half>::equals(Half(UnsignedShort(0xabcd)),
+                                            Half(UnsignedShort(0xabcd))));
+    CORRADE_VERIFY(!TypeTraits<Half>::equals(Half(UnsignedShort(0xabcd)),
+                                            Half(UnsignedShort(0xabce))));
+}
+
 template<class T> void TypeTraitsTest::equalsFloatingPoint0() {
     setTestCaseTemplateName(TypeTraits<T>::name());
 
diff --git a/src/Magnum/Math/TypeTraits.h b/src/Magnum/Math/TypeTraits.h
index 4b3b31728..b9412a2ba 100644
--- a/src/Magnum/Math/TypeTraits.h
+++ b/src/Magnum/Math/TypeTraits.h
@@ -85,9 +85,8 @@ namespace Magnum { namespace Math {
 @m_since{2019,10}
 
 Equivalent to @ref std::true_type for all builtin scalar integer and
-floating-point types and in addition also @ref Deg and @ref Rad; equivalent to
-@ref std::false_type otherwise. The @ref Half type deliberately doesn't support
-any arithmetic, so it's not treated as a scalar type.
+floating-point types and in addition also @ref Half, @ref Deg and @ref Rad;
+equivalent to @ref std::false_type otherwise.
 
 Note that this is *different* from @ref std::is_scalar, which is @cpp true @ce
 also for enums or pointers --- it's rather closer to @ref std::is_arithmetic,
@@ -117,6 +116,7 @@ template<> struct IsScalar<unsigned long>: std::true_type {};
 template<> struct IsScalar<long long>: std::true_type {};
 template<> struct IsScalar<unsigned long long>: std::true_type {};
 template<> struct IsScalar<float>: std::true_type {};
+template<> struct IsScalar<Half>: std::true_type {};
 template<> struct IsScalar<double>: std::true_type {};
 #ifndef CORRADE_TARGET_EMSCRIPTEN
 template<> struct IsScalar<long double>: std::true_type {};
@@ -196,9 +196,8 @@ template<class T> struct IsIntegral<Color4<T>>: IsIntegral<T> {};
 @m_since{2019,10}
 
 Equivalent to @ref std::true_type for all floating-point scalar and vector
-types supported by Magnum math including @ref Deg and @ref Rad; equivalent to
-@ref std::false_type otherwise. The @ref Half type deliberately doesn't support
-any arithmetic, so it's not treated as a floating-point type.
+types supported by Magnum math including @ref Half, @ref Deg and @ref Rad;
+equivalent to @ref std::false_type otherwise.
 @see @ref IsIntegral, @ref IsScalar, @ref IsVector, @ref std::is_floating_point
 */
 template<class T> struct IsFloatingPoint
@@ -209,6 +208,7 @@ template<class T> struct IsFloatingPoint
 
 #ifndef DOXYGEN_GENERATING_OUTPUT
 template<> struct IsFloatingPoint<Float>: std::true_type {};
+template<> struct IsFloatingPoint<Half>: std::true_type {};
 template<> struct IsFloatingPoint<Double>: std::true_type {};
 #ifndef CORRADE_TARGET_EMSCRIPTEN
 template<> struct IsFloatingPoint<long double>: std::true_type {};
@@ -346,8 +346,10 @@ template<class T> struct TypeTraits: Implementation::TypeTraitsDefault<T> {
     /**
      * @brief Fuzzy compare
      *
-     * Uses fuzzy compare for floating-point types (using @ref epsilon()
-     * value), pure equality comparison everywhere else. Algorithm adapted from
+     * Uses fuzzy compare for all floating-point types except @ref Half (using
+     * the @ref epsilon() value), pure equality comparison everywhere else.
+     * The @ref Half type has representable values sparse enough that no fuzzy
+     * comparison needs to be done. Algorithm adapted from
      * http://floating-point-gui.de/errors/comparison/.
      * @see @ref Math::equal(T, T), @ref Math::notEqual(T, T)
      */
@@ -410,6 +412,7 @@ namespace Implementation {
     _c(Long)
     #endif
     _c(Float)
+    _c(Half)
     _c(Double)
     #ifndef CORRADE_TARGET_EMSCRIPTEN
     _c(long double)
@@ -498,6 +501,11 @@ template<> struct TypeTraits<Float>: Implementation::TypeTraitsFloatingPoint<Flo
 
     constexpr static Float epsilon() { return FLOAT_EQUALITY_PRECISION; }
 };
+/* A bit special -- using integer comparison for equality but presenting itself
+   as a floating-point type so Color's fullChannel() works correctly */
+template<> struct TypeTraits<Half>: Implementation::TypeTraitsName<Half>, Implementation::TypeTraitsDefault<Half> {
+    typedef Half FloatingPointType;
+};
 template<> struct TypeTraits<Double>: Implementation::TypeTraitsFloatingPoint<Double> {
     typedef Double FloatingPointType;