traits: add native conversion functions

traits.hpp

@@ -112,11 +112,69 @@ namespace cruft::vk {
     #undef IS_WRAPPER
 
 
+    //-------------------------------------------------------------------------
+    template <typename T>
+    struct is_wrapper<owned_ptr<T>> :
+        public is_wrapper<T>
+    { };
+
+
     //-------------------------------------------------------------------------
     template <typename T>
     static constexpr auto is_wrapper_v = is_wrapper<T>::value;
 
 
+    ///////////////////////////////////////////////////////////////////////////
+    /// return the native value for the wrapper object
+    template <typename SelfT>
+    constexpr auto
+    native (const object<SelfT> &obj)
+    {
+        return obj.native ();
+    }
+
+
+    ///------------------------------------------------------------------------
+    /// return the native handle as is; supplied for implementation convenience
+    /// in other higher order methods.
+    template <
+        typename NativeT,
+        typename = std::enable_if_t<is_native_v<NativeT>, void>
+    >
+    constexpr auto
+    native (NativeT val)
+    {
+        return val;
+    }
+
+
+    ///------------------------------------------------------------------------
+    /// return the underlying native value by querying the data object (not the
+    /// owner object).
+    template <typename SelfT>
+    constexpr auto
+    native (const owned_ptr<SelfT> &ptr)
+    {
+        return native (ptr.get ());
+    }
+
+
+    ///------------------------------------------------------------------------
+    /// try to return the vulkan native type if there is one, else return the
+    /// value we were given.
+    template <typename T, typename DecayT = std::decay_t<T>>
+    constexpr auto
+    maybe_native (T &&t)
+    {
+        if constexpr (is_wrapper_v<DecayT>)
+            return native (t);
+        else if constexpr (is_native_v<DecayT>)
+            return native (t);
+        else
+            return t;
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     /// describes the corresponding value for sType in native structures
     template <typename>