[core] Merge PiecewiseConstantFunction into Function

1 files changed, 30 insertions, 1 deletions

diff --git a/src/mbgl/style/function.hpp b/src/mbgl/style/function.hpp
index 6ef4fcf5da..e28b0efdd9 100644
--- a/src/mbgl/style/function.hpp
+++ b/src/mbgl/style/function.hpp
@@ -1,11 +1,18 @@
 #ifndef MBGL_STYLE_FUNCTION
 #define MBGL_STYLE_FUNCTION
 
+#include <mbgl/style/types.hpp>
+#include <mbgl/util/chrono.hpp>
+
+#include <mapbox/optional.hpp>
+
 #include <vector>
 #include <utility>
 
 namespace mbgl {
 
+class StyleCalculationParameters;
+
 template <typename T>
 class Function {
 public:
@@ -19,13 +26,35 @@ public:
     explicit Function(const Stops& stops_, float base_)
         : base(base_), stops(stops_) {}
 
-    T evaluate(float z) const;
+    T evaluate(const StyleCalculationParameters&) const;
 
 private:
     const float base = 1;
     const std::vector<std::pair<float, T>> stops;
 };
 
+// Partial specialization for cross-faded properties (*-pattern, line-dasharray).
+template <typename T>
+class Function<Faded<T>> {
+public:
+    using Stop = std::pair<float, T>;
+    using Stops = std::vector<Stop>;
+
+    // TODO: make explicit
+    /* explicit */ Function(const T& constant)
+        : stops({{ 0, constant }}) {}
+
+    explicit Function(const Stops& stops_,
+                      mapbox::util::optional<Duration> duration_)
+        : stops(stops_), duration(duration_) {}
+
+    Faded<T> evaluate(const StyleCalculationParameters&) const;
+
+private:
+    const std::vector<std::pair<float, T>> stops;
+    const mapbox::util::optional<Duration> duration = {};
+};
+
 }
 
 #endif