[core] Add support for data-driven styling

1 files changed, 49 insertions, 0 deletions

diff --git a/include/mbgl/style/function/interval_stops.hpp b/include/mbgl/style/function/interval_stops.hpp
new file mode 100644
index 0000000000..cf879d730b
--- /dev/null
+++ b/include/mbgl/style/function/interval_stops.hpp
@@ -0,0 +1,49 @@
+#pragma once
+
+#include <mbgl/util/feature.hpp>
+
+#include <map>
+
+namespace mbgl {
+namespace style {
+
+template <class T>
+class IntervalStops {
+public:
+    using Stops = std::map<float, T>;
+    Stops stops;
+
+    IntervalStops() = default;
+    IntervalStops(Stops stops_)
+        : stops(std::move(stops_)) {
+    }
+
+    T evaluate(const Value& value) const {
+        if (stops.empty()) {
+            assert(false);
+            return T();
+        }
+
+        optional<float> z = numericValue<float>(value);
+        if (!z) {
+            return T();
+        }
+
+        auto it = stops.upper_bound(*z);
+        if (it == stops.end()) {
+            return stops.rbegin()->second;
+        } else if (it == stops.begin()) {
+            return stops.begin()->second;
+        } else {
+            return std::prev(it)->second;
+        }
+    }
+
+    friend bool operator==(const IntervalStops& lhs,
+                           const IntervalStops& rhs) {
+        return lhs.stops == rhs.stops;
+    }
+};
+
+} // namespace style
+} // namespace mbgl