[core] Render fill-extrusion layers (#8431)

1 files changed, 56 insertions, 0 deletions

diff --git a/include/mbgl/util/indexed_tuple.hpp b/include/mbgl/util/indexed_tuple.hpp
new file mode 100644
index 0000000000..a414639530
--- /dev/null
+++ b/include/mbgl/util/indexed_tuple.hpp
@@ -0,0 +1,56 @@
+#pragma once
+
+#include <mbgl/util/type_list.hpp>
+
+#include <type_traits>
+#include <tuple>
+
+namespace mbgl {
+
+template <class T, class... Ts>
+struct TypeIndex;
+
+template <class T, class... Ts>
+struct TypeIndex<T, T, Ts...> : std::integral_constant<std::size_t, 0> {};
+
+template <class T, class U, class... Ts>
+struct TypeIndex<T, U, Ts...> : std::integral_constant<std::size_t, 1 + TypeIndex<T, Ts...>::value> {};
+
+template <class...> class IndexedTuple;
+
+// A tuple of Ts, where individual members can be accessed via `t.get<I>()` for I ∈ Is.
+//
+// See https://github.com/mapbox/cpp/blob/master/C%2B%2B%20Structural%20Metaprogramming.md
+// for motivation.
+//
+template <class... Is, class... Ts>
+class IndexedTuple<TypeList<Is...>, TypeList<Ts...>> : public std::tuple<Ts...> {
+public:
+    static_assert(sizeof...(Is) == sizeof...(Ts), "IndexedTuple size mismatch");
+
+    using std::tuple<Ts...>::tuple;
+
+    template <class I>
+    static constexpr std::size_t Index = TypeIndex<I, Is...>::value;
+
+    template <class I>
+    auto& get() {
+        return std::get<Index<I>>(*this);
+    }
+
+    template <class I>
+    const auto& get() const {
+        return std::get<Index<I>>(*this);
+    }
+
+    template <class... Js, class... Us>
+    IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>>
+    concat(const IndexedTuple<TypeList<Js...>, TypeList<Us...>>& other) const {
+        return IndexedTuple<TypeList<Is..., Js...>, TypeList<Ts..., Us...>> {
+            get<Is>()...,
+            other.template get<Js>()...
+        };
+    }
+};
+
+} // namespace mbgl