@@ -399,8 +399,15 @@ either

 -   `T` itself, if `T` is a [scalar][]

 then `constexpr auto GLTraits::members<T>()` returns an instance of the

-[empty][] `struct GLTraits::Members<typename T, typename... Values>` where

-`Values...` are the ("member") types above, in the order they occur in `T`.

+[empty][] `struct GLTraits::Members<typename T, typename... Members>` where

+each of `Members...` is `GLTraits::Member<typename Value, std::size_t offset>`

+that describe the ("member") types above, in the order they occur in `T`.

+`Value` is the type of the member and `offset` is the offset of the member in

+`T`. Note that `offset` is only correct if the padding in `T` is minimal while

+still satisfying the [`alignof`][] of the member types. The author knows of no

+compiler that breaks this assumption unless explicitly instructed (e.g. with

+[`alignas`][], which are not taken into account), however the standard allows

+it.

 An example use case would be along the lines of:

@@ -408,26 +415,22 @@ An example use case would be along the lines of:

 template<

     typename    T,

     typename    Value,

-    typename... Values

+    std::size_t offset,

+    typename... Members

 >

 void vertex_setup(

-    GLTraits::Members<T, Value, Values...>,

-    std::size_t offset   = 0,

-    GLint       location = 0

+    GLTraits::Members<T, GLTraits::Member<Value, offset>, Members...>,

+    GLint location = 0

 )

 {

-    auto unaligned = offset % alignof(Value);

-    if (unaligned)

-        offset += alignof(Value) - unaligned;

     GLTraits::Value<Value>::vertex_attrib_pointer(location, offset, sizeof(T));

     vertex_setup(

-        GLTraits::Members<T, Values...>{},

-        offset   + sizeof(Value),

+        GLTraits::Members<T, Members...>{},

         location + GLTraits::Value<Value>::columns

     );

 }

 template<typename T>

-void vertex_setup(GLTraits::Members<T>, std::size_t, GLint)

+void vertex_setup(GLTraits::Members<T>, GLint)

 {}

 struct Vertex

@@ -462,6 +465,8 @@ version [`magic_get`][]) on whose talks this implementation is based:

 [class]: https://en.cppreference.com/w/cpp/types/is_class

 [array]: https://en.cppreference.com/w/cpp/types/is_array

 [scalar]: https://en.cppreference.com/w/cpp/types/is_scalar

+[`alignof`]: https://en.cppreference.com/w/cpp/language/alignof

+[`alignas`]: https://en.cppreference.com/w/cpp/language/alignas

 [`tests/vertex_setup.cpp`]: tests/vertex_setup.cpp

 [`doc/vertex_setup`]: doc/vertex_setup

 [`doc/vertex_setup.i`]: doc/vertex_setup.i

@@ -42,7 +42,11 @@ public:

     #if __cplusplus >= 201402L

-    template<typename T, typename... Value>

+    template<typename Value, std::size_t offset>

+    struct Member

+    {};

+

+    template<typename T, typename... Member>

     struct Members

     {};

@@ -101,7 +105,8 @@ private:

     struct MemberInfo

     {

-        GLenum id;

+        GLenum      id;

+        std::size_t offset;

     };

     template<std::size_t N>

@@ -114,11 +119,18 @@ private:

     {

         MemberInfo * info;

+        constexpr static auto align(std::size_t align, std::size_t offset)

+        {

+            return ((offset - 1) / align + 1) * align;

+        }

+

         template<typename Value>

         constexpr operator Value()

         {

             return (

-                info->id = GLTraits::Value<Value>::id,

+                info[0].id     = GLTraits::Value<Value>::id,

+                info[0].offset = align(alignof(Value), info[0].offset),

+                info[1].offset = info[0].offset + sizeof(Value),

                 Value{}

             );

         }

@@ -144,7 +156,7 @@ private:

     }

     template<typename T, std::size_t... Is>

-    static constexpr auto member_infos(MemberInfos<sizeof...(Is)> infos = {})

+    static constexpr auto member_infos(MemberInfos<sizeof...(Is)+1> infos = {})

     {

         return ((void)T{MemberAny{&infos.infos[Is]}...}, infos);

     }

@@ -154,7 +166,10 @@ private:

     {

         return Members<

             T,

-            typename ValueID<member_infos<T, Is...>().infos[Is].id>::Value...

+            Member<

+                typename ValueID<member_infos<T, Is...>().infos[Is].id>::Value,

+                member_infos<T, Is...>().infos[Is].offset

+            >...

         >{};

     }

@@ -113,24 +113,25 @@ struct GLTraitsTest : protected GLBase

     template<

         typename    T,

         typename    Value,

-        typename... Values

+        std::size_t offset,

+        typename... Members

     >

     void static test_members(

-        GLTraits::Members<T, Value, Values...>,

-        std::size_t offset = 0

+        GLTraits::Members<T, GLTraits::Member<Value, offset>, Members...>

     )

     {

-        auto unaligned = offset % alignof(Value);

-        if (unaligned)

-            offset += alignof(Value) - unaligned;

-        auto end = offset + sizeof(Value);

+        auto constexpr end = offset + sizeof(Value);

         using Traits = GLTraits::Value<Value>;

         static_assert(

             std::is_empty<GLTraits::Members<

-                T, Value, Values...

+                T, GLTraits::Member<Value, offset>, Members...

             >>::value,

             "GLTraits::Members must be empty"

         );

+        static_assert(

+            std::is_empty<GLTraits::Member<Value, offset>>::value,

+            "GLTraits::Member must be empty"

+        );

         #define GLTRAITS_TEST_MEMBERS(IND, NAME, OFFSET, END) \

             std::cout \

                 << std::left  << std::setw(IND)           << "" \

@@ -138,10 +139,10 @@ struct GLTraitsTest : protected GLBase

                 << std::right << std::setw(2) << std::dec << OFFSET << " " \

                 << std::right << std::setw(3) << std::dec << END    << "\n";

         GLTRAITS_TEST_MEMBERS(2, Traits::name, offset, end)

-        test_members(GLTraits::Members<T, Values...>{}, end);

+        test_members(GLTraits::Members<T, Members...>{});

     }

     template<typename T>

-    void static test_members(GLTraits::Members<T>, std::size_t)

+    void static test_members(GLTraits::Members<T>)

     {}

     #endif

@@ -9,26 +9,22 @@

 template<

     typename    T,

     typename    Value,

-    typename... Values

+    std::size_t offset,

+    typename... Members

 >

 void vertex_setup(

-    GLTraits::Members<T, Value, Values...>,

-    std::size_t offset   = 0,

-    GLint       location = 0

+    GLTraits::Members<T, GLTraits::Member<Value, offset>, Members...>,

+    GLint location = 0

 )

 {

-    auto unaligned = offset % alignof(Value);

-    if (unaligned)

-        offset += alignof(Value) - unaligned;

     GLTraits::Value<Value>::vertex_attrib_pointer(location, offset, sizeof(T));

     vertex_setup(

-        GLTraits::Members<T, Values...>{},

-        offset   + sizeof(Value),

+        GLTraits::Members<T, Members...>{},

         location + GLTraits::Value<Value>::columns

     );

 }

 template<typename T>

-void vertex_setup(GLTraits::Members<T>, std::size_t, GLint)

+void vertex_setup(GLTraits::Members<T>, GLint)

 {}