[core] Move interpolate.hpp to public include directory

1 files changed, 89 insertions, 0 deletions

diff --git a/include/mbgl/util/interpolate.hpp b/include/mbgl/util/interpolate.hpp
new file mode 100644
index 0000000000..d463ffc056
--- /dev/null
+++ b/include/mbgl/util/interpolate.hpp
@@ -0,0 +1,89 @@
+#pragma once
+
+#include <mbgl/util/color.hpp>
+#include <mbgl/util/range.hpp>
+
+#include <array>
+#include <vector>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+namespace mbgl {
+namespace util {
+
+float interpolationFactor(float base, Range<float> range, float z);
+
+template <class T, class Enabled = void>
+struct Interpolator;
+
+template <typename T>
+T interpolate(const T& a, const T& b, const double t) {
+    return Interpolator<T>()(a, b, t);
+}
+
+
+template <class T, class Enabled>
+struct Interpolator {
+    T operator()(const T& a, const T& b, const double t) const {
+        return a * (1.0 - t) + b * t;
+    }
+};
+
+template <class T, std::size_t N>
+struct Interpolator<std::array<T, N>> {
+private:
+    using Array = std::array<T, N>;
+
+    template <std::size_t... I>
+    Array operator()(const Array& a, const Array& b, const double t, std::index_sequence<I...>) {
+        return {{ interpolate(a[I], b[I], t)... }};
+    }
+
+public:
+    Array operator()(const Array& a, const Array& b, const double t) {
+        return operator()(a, b, t, std::make_index_sequence<N>());
+    }
+};
+
+template <>
+struct Interpolator<Color> {
+public:
+    Color operator()(const Color& a, const Color& b, const double t) {
+        return {
+            interpolate(a.r, b.r, t),
+            interpolate(a.g, b.g, t),
+            interpolate(a.b, b.b, t),
+            interpolate(a.a, b.a, t)
+        };
+    }
+};
+
+struct Uninterpolated {
+    template <class T>
+    T operator()(const T& a, const T&, const double) const {
+        return a;
+    }
+};
+
+template <>
+struct Interpolator<bool>
+    : Uninterpolated {};
+
+template <class T>
+struct Interpolator<T, typename std::enable_if_t<std::is_enum<T>::value>>
+    : Uninterpolated {};
+
+template <>
+struct Interpolator<std::string>
+    : Uninterpolated {};
+
+template <class T>
+struct Interpolator<std::vector<T>>
+    : Uninterpolated {};
+
+template <class T>
+constexpr bool Interpolatable = !std::is_base_of<Uninterpolated, Interpolator<T>>::value;
+
+} // namespace util
+} // namespace mbgl