1 files changed, 79 insertions, 0 deletions
diff --git a/include/mbgl/style/function_properties.hpp b/include/mbgl/style/function_properties.hpp
new file mode 100644
index 0000000000..74ac80f83c
--- /dev/null
+++ b/include/mbgl/style/function_properties.hpp
@@ -0,0 +1,79 @@
+#ifndef MBGL_STYLE_FUNCTION_PROPERTIES
+#define MBGL_STYLE_FUNCTION_PROPERTIES
+
+#include <mbgl/util/variant.hpp>
+
+#include <vector>
+
+namespace mbgl {
+
+template <typename T>
+struct ConstantFunction {
+    inline ConstantFunction(const T &value) : value(value) {}
+    inline T evaluate(float) const { return value; }
+
+private:
+    const T value;
+};
+
+template <typename T>
+struct LinearFunction {
+    inline LinearFunction(const T &value, float z_base, float slope, const T &min, const T &max)
+        : value(value), min(min), max(max), z_base(z_base), slope(slope) {}
+    T evaluate(float z) const;
+
+private:
+    const T value, min, max;
+    const float z_base, slope;
+};
+
+template <typename T>
+struct ExponentialFunction {
+    inline ExponentialFunction(const T &value, float z_base, float exp_base, float slope, const T &min,
+                               const T &max)
+        : value(value), min(min), max(max), z_base(z_base), exp_base(exp_base), slope(slope) {}
+    T evaluate(float z) const;
+
+private:
+    const T value, min, max;
+    const float z_base, exp_base, slope;
+};
+
+template <typename T>
+struct StopsFunction {
+    inline StopsFunction(const std::vector<std::pair<float, T>> &values) : values(values) {}
+    T evaluate(float z) const;
+
+private:
+    const std::vector<std::pair<float, T>> values;
+};
+
+template <typename T>
+using Function = util::variant<
+    std::false_type,
+    ConstantFunction<T>,
+    LinearFunction<T>,
+    ExponentialFunction<T>,
+    StopsFunction<T>
+>;
+
+template <typename T>
+struct FunctionEvaluator {
+    typedef T result_type;
+    inline FunctionEvaluator(float z) : z(z) {}
+
+    inline result_type operator()(const std::false_type &) {
+        return result_type();
+    }
+
+    template <template <typename> class Fn>
+    inline result_type operator()(const Fn<T>& fn) {
+        return fn.evaluate(z);
+    }
+private:
+    float z;
+};
+
+}
+
+#endif