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#pragma once
#include <mbgl/util/type_list.hpp>
#include <mbgl/util/indexed_tuple.hpp>
#include <array>
#include <type_traits>
#include <cstddef>
#define MBGL_DEFINE_ATTRIBUTE(type_, n_, name_) \
struct name_ { \
using Type = ::mbgl::gfx::AttributeType<type_, n_>; \
static auto name() { \
return #name_; \
} \
}
#define MBGL_VERTEX_ALIGN __attribute__((aligned(4)))
namespace mbgl {
namespace gfx {
template <typename T, std::size_t N>
class AttributeType {
public:
using ValueType = T;
static constexpr size_t Dimensions = N;
using Value = std::array<T, N>;
};
struct VertexDescriptor {
const uint8_t size;
const uint8_t count;
const uint8_t offsets[5];
};
// Attribute binding requires member offsets. The only standard way to
// obtain an offset is the offsetof macro. The offsetof macro has defined
// behavior only for standard layout types. That rules out std::tuple and
// any other solution that relies on chained inheritance. Manually implemented
// variadic specialization looks like the only solution. Fortunately, we
// only use a maximum of five attributes.
namespace detail {
template <class...>
struct Vertex;
template <class A1>
struct Vertex<A1> {
using Type = Vertex<A1>;
A1 a1;
} MBGL_VERTEX_ALIGN;
template <class A1, class A2>
struct Vertex<A1, A2> {
using Type = Vertex<A1, A2>;
A1 a1;
A2 a2;
} MBGL_VERTEX_ALIGN;
template <class A1, class A2, class A3>
struct Vertex<A1, A2, A3> {
using Type = Vertex<A1, A2, A3>;
A1 a1;
A2 a2;
A3 a3;
} MBGL_VERTEX_ALIGN;
template <class A1, class A2, class A3, class A4>
struct Vertex<A1, A2, A3, A4> {
using Type = Vertex<A1, A2, A3, A4>;
A1 a1;
A2 a2;
A3 a3;
A4 a4;
} MBGL_VERTEX_ALIGN;
template <class A1, class A2, class A3, class A4, class A5>
struct Vertex<A1, A2, A3, A4, A5> {
using Type = Vertex<A1, A2, A3, A4, A5>;
A1 a1;
A2 a2;
A3 a3;
A4 a4;
A5 a5;
} MBGL_VERTEX_ALIGN;
template <class>
struct Descriptor;
template <class A1>
struct Descriptor<Vertex<A1>> {
using Type = Vertex<A1>;
static_assert(sizeof(Type) < 256, "vertex type must be smaller than 256 bytes");
static_assert(std::is_standard_layout<Type>::value, "vertex type must use standard layout");
static constexpr const VertexDescriptor Data = { sizeof(Type), 1, {
offsetof(Type, a1),
}};
};
template <class A1, class A2>
struct Descriptor<Vertex<A1, A2>> {
using Type = Vertex<A1, A2>;
static_assert(sizeof(Type) < 256, "vertex type must be smaller than 256 bytes");
static_assert(std::is_standard_layout<Type>::value, "vertex type must use standard layout");
static constexpr const VertexDescriptor Data = { sizeof(Type), 2, {
offsetof(Type, a1),
offsetof(Type, a2),
}};
};
template <class A1, class A2, class A3>
struct Descriptor<Vertex<A1, A2, A3>> {
using Type = Vertex<A1, A2, A3>;
static_assert(sizeof(Type) < 256, "vertex type must be smaller than 256 bytes");
static_assert(std::is_standard_layout<Type>::value, "vertex type must use standard layout");
static constexpr const VertexDescriptor Data = { sizeof(Type), 3, {
offsetof(Type, a1),
offsetof(Type, a2),
offsetof(Type, a3),
}};
};
template <class A1, class A2, class A3, class A4>
struct Descriptor<Vertex<A1, A2, A3, A4>> {
using Type = Vertex<A1, A2, A3, A4>;
static_assert(sizeof(Type) < 256, "vertex type must be smaller than 256 bytes");
static_assert(std::is_standard_layout<Type>::value, "vertex type must use standard layout");
static constexpr const VertexDescriptor Data = { sizeof(Type), 4, {
offsetof(Type, a1),
offsetof(Type, a2),
offsetof(Type, a3),
offsetof(Type, a4),
}};
};
template <class A1, class A2, class A3, class A4, class A5>
struct Descriptor<Vertex<A1, A2, A3, A4, A5>> {
using Type = Vertex<A1, A2, A3, A4, A5>;
static_assert(sizeof(Type) < 256, "vertex type must be smaller than 256 bytes");
static_assert(std::is_standard_layout<Type>::value, "vertex type must use standard layout");
static constexpr const VertexDescriptor Data = { sizeof(Type), 5, {
offsetof(Type, a1),
offsetof(Type, a2),
offsetof(Type, a3),
offsetof(Type, a4),
offsetof(Type, a5),
}};
};
template <class... As>
struct Vertex<TypeList<As...>> {
using Type = Vertex<typename As::Type::Value...>;
};
} // namespace detail
template <class A>
using Vertex = typename detail::Vertex<A>::Type;
template <class V>
constexpr const VertexDescriptor vertexDescriptor = detail::Descriptor<V>::Data;
} // namespace gfx
} // namespace mbgl
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