[core] Add support for data-driven styling

4 files changed, 355 insertions, 38 deletions

diff --git a/include/mbgl/style/conversion/data_driven_property_value.hpp b/include/mbgl/style/conversion/data_driven_property_value.hpp
new file mode 100644
index 0000000000..83f44fdb27
--- /dev/null
+++ b/include/mbgl/style/conversion/data_driven_property_value.hpp
@@ -0,0 +1,46 @@
+#pragma once
+
+#include <mbgl/style/data_driven_property_value.hpp>
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/style/conversion/constant.hpp>
+#include <mbgl/style/conversion/function.hpp>
+
+namespace mbgl {
+namespace style {
+namespace conversion {
+
+template <class T>
+struct Converter<DataDrivenPropertyValue<T>> {
+    template <class V>
+    Result<DataDrivenPropertyValue<T>> operator()(const V& value) const {
+        if (isUndefined(value)) {
+            return {};
+        } else if (!isObject(value)) {
+            Result<T> constant = convert<T>(value);
+            if (!constant) {
+                return constant.error();
+            }
+            return DataDrivenPropertyValue<T>(*constant);
+        } else if (!objectMember(value, "property")) {
+            Result<CameraFunction<T>> function = convert<CameraFunction<T>>(value);
+            if (!function) {
+                return function.error();
+            }
+            return DataDrivenPropertyValue<T>(*function);
+        } else {
+            Result<CompositeFunction<T>> composite = convert<CompositeFunction<T>>(value);
+            if (composite) {
+                return DataDrivenPropertyValue<T>(*composite);
+            }
+            Result<SourceFunction<T>> source = convert<SourceFunction<T>>(value);
+            if (!source) {
+                return source.error();
+            }
+            return DataDrivenPropertyValue<T>(*source);
+        }
+    }
+};
+
+} // namespace conversion
+} // namespace style
+} // namespace mbgl
diff --git a/include/mbgl/style/conversion/function.hpp b/include/mbgl/style/conversion/function.hpp
index 6a0b67618f..90b4b95063 100644
--- a/include/mbgl/style/conversion/function.hpp
+++ b/include/mbgl/style/conversion/function.hpp
@@ -1,70 +1,340 @@
 #pragma once
 
-#include <mbgl/style/function.hpp>
+#include <mbgl/style/function/camera_function.hpp>
+#include <mbgl/style/function/source_function.hpp>
+#include <mbgl/style/function/composite_function.hpp>
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/constant.hpp>
+#include <mbgl/util/ignore.hpp>
 
 namespace mbgl {
 namespace style {
 namespace conversion {
 
+template <class D, class R, class V>
+Result<std::map<D, R>> convertStops(const V& value) {
+    auto stopsValue = objectMember(value, "stops");
+    if (!stopsValue) {
+        return Error { "function value must specify stops" };
+    }
+
+    if (!isArray(*stopsValue)) {
+        return Error { "function stops must be an array" };
+    }
+
+    if (arrayLength(*stopsValue) == 0) {
+        return Error { "function must have at least one stop" };
+    }
+
+    std::map<D, R> stops;
+    for (std::size_t i = 0; i < arrayLength(*stopsValue); ++i) {
+        const auto& stopValue = arrayMember(*stopsValue, i);
+
+        if (!isArray(stopValue)) {
+            return Error { "function stop must be an array" };
+        }
+
+        if (arrayLength(stopValue) != 2) {
+            return Error { "function stop must have two elements" };
+        }
+
+        Result<D> d = convert<D>(arrayMember(stopValue, 0));
+        if (!d) {
+            return d.error();
+        }
+
+        Result<R> r = convert<R>(arrayMember(stopValue, 1));
+        if (!r) {
+            return r.error();
+        }
+
+        stops.emplace(*d, *r);
+    }
+
+    return stops;
+}
+
 template <class T>
-struct Converter<Function<T>> {
+struct Converter<ExponentialStops<T>> {
+    static constexpr const char * type = "exponential";
+
     template <class V>
-    Result<Function<T>> operator()(const V& value) const {
+    Result<ExponentialStops<T>> operator()(const V& value) const {
+        auto stops = convertStops<float, T>(value);
+        if (!stops) {
+            return stops.error();
+        }
+
+        auto baseValue = objectMember(value, "base");
+        if (!baseValue) {
+            return ExponentialStops<T>(*stops);
+        }
+
+        optional<float> base = toNumber(*baseValue);
+        if (!base) {
+            return Error { "function base must be a number"};
+        }
+
+        return ExponentialStops<T>(*stops, *base);
+    }
+};
+
+template <class T>
+struct Converter<IntervalStops<T>> {
+    static constexpr const char * type = "interval";
+
+    template <class V>
+    Result<IntervalStops<T>> operator()(const V& value) const {
+        auto stops = convertStops<float, T>(value);
+        if (!stops) {
+            return stops.error();
+        }
+        return IntervalStops<T>(*stops);
+    }
+};
+
+template <>
+struct Converter<CategoricalValue> {
+    template <class V>
+    Result<CategoricalValue> operator()(const V& value) const {
+        auto b = toBool(value);
+        if (b) {
+            return *b;
+        }
+
+        auto n = toNumber(value);
+        if (n) {
+            return int64_t(*n);
+        }
+
+        auto s = toString(value);
+        if (s) {
+            return *s;
+        }
+
+        return Error { "stop domain value must be a number, string, or boolean" };
+    }
+};
+
+template <class T>
+struct Converter<CategoricalStops<T>> {
+    static constexpr const char * type = "categorical";
+
+    template <class V>
+    Result<CategoricalStops<T>> operator()(const V& value) const {
+        auto stops = convertStops<CategoricalValue, T>(value);
+        if (!stops) {
+            return stops.error();
+        }
+        return CategoricalStops<T>(
+            std::map<CategoricalValue, T>((*stops).begin(), (*stops).end()));
+    }
+};
+
+template <class T>
+struct Converter<IdentityStops<T>> {
+    static constexpr const char * type = "identity";
+
+    template <class V>
+    Result<IdentityStops<T>> operator()(const V&) const {
+        return IdentityStops<T>();
+    }
+};
+
+template <class, class>
+struct StopsConverter;
+
+template <class T, class... Ts>
+struct StopsConverter<T, variant<Ts...>> {
+public:
+    template <class V>
+    Result<variant<Ts...>> operator()(const V& value) const {
+        std::string type = util::Interpolatable<T> ? "exponential" : "interval";
+
+        auto typeValue = objectMember(value, "type");
+        if (typeValue && toString(*typeValue)) {
+            type = *toString(*typeValue);
+        }
+
+        optional<Result<variant<Ts...>>> result;
+
+        // Workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47226
+        auto tryConvert = [&] (auto* tp) {
+            using Stops = std::decay_t<decltype(*tp)>;
+            if (type == Converter<Stops>::type) {
+                auto stops = convert<Stops>(value);
+                result = stops
+                    ? Result<variant<Ts...>>(*stops)
+                    : Result<variant<Ts...>>(stops.error());
+            }
+        };
+
+        util::ignore({
+            (tryConvert((Ts*)nullptr), 0)...
+        });
+
+        if (!result) {
+            return Error { "unsupported function type" };
+        }
+
+        return *result;
+    }
+};
+
+template <class T>
+struct Converter<CameraFunction<T>> {
+    template <class V>
+    Result<CameraFunction<T>> operator()(const V& value) const {
+        if (!isObject(value)) {
+            return Error { "function must be an object" };
+        }
+
+        auto stops = StopsConverter<T, typename CameraFunction<T>::Stops>()(value);
+        if (!stops) {
+            return stops.error();
+        }
+
+        return CameraFunction<T>(*stops);
+    }
+};
+
+template <class T>
+struct Converter<SourceFunction<T>> {
+    template <class V>
+    Result<SourceFunction<T>> operator()(const V& value) const {
+        if (!isObject(value)) {
+            return Error { "function must be an object" };
+        }
+
+        auto propertyValue = objectMember(value, "property");
+        if (!propertyValue) {
+            return Error { "function must specify property" };
+        }
+
+        auto propertyString = toString(*propertyValue);
+        if (!propertyString) {
+            return Error { "function property must be a string" };
+        }
+
+        auto stops = StopsConverter<T, typename SourceFunction<T>::Stops>()(value);
+        if (!stops) {
+            return stops.error();
+        }
+
+        return SourceFunction<T>(*propertyString, *stops);
+    }
+};
+
+template <class S>
+struct CompositeValue : std::pair<float, S> {
+    using std::pair<float, S>::pair;
+};
+
+template <class S>
+struct Converter<CompositeValue<S>> {
+    template <class V>
+    Result<CompositeValue<S>> operator()(const V& value) const {
+        if (!isObject(value)) {
+            return Error { "stop must be an object" };
+        }
+
+        auto zoomValue = objectMember(value, "zoom");
+        if (!zoomValue) {
+            return Error { "stop must specify zoom" };
+        }
+
+        auto propertyValue = objectMember(value, "value");
+        if (!propertyValue) {
+            return Error { "stop must specify value" };
+        }
+
+        Result<float> z = convert<float>(*zoomValue);
+        if (!z) {
+            return z.error();
+        }
+
+        Result<S> s = convert<S>(*propertyValue);
+        if (!s) {
+            return s.error();
+        }
+
+        return CompositeValue<S> { *z, *s };
+    }
+};
+
+template <class T>
+struct Converter<CompositeFunction<T>> {
+    template <class V>
+    Result<CompositeFunction<T>> operator()(const V& value) const {
         if (!isObject(value)) {
             return Error { "function must be an object" };
         }
 
-        auto stopsValue = objectMember(value, "stops");
-        if (!stopsValue) {
-            return Error { "function value must specify stops" };
+        auto propertyValue = objectMember(value, "property");
+        if (!propertyValue) {
+            return Error { "function must specify property" };
         }
 
-        if (!isArray(*stopsValue)) {
-            return Error { "function stops must be an array" };
+        auto propertyString = toString(*propertyValue);
+        if (!propertyString) {
+            return Error { "function property must be a string" };
         }
 
-        if (arrayLength(*stopsValue) == 0) {
-            return Error { "function must have at least one stop" };
+        std::string type = "exponential";
+        auto typeValue = objectMember(value, "type");
+        if (typeValue && toString(*typeValue)) {
+            type = *toString(*typeValue);
         }
 
-        std::vector<std::pair<float, T>> stops;
-        for (std::size_t i = 0; i < arrayLength(*stopsValue); ++i) {
-            const auto& stopValue = arrayMember(*stopsValue, i);
+        if (type == "exponential") {
+            auto stops = convertStops<CompositeValue<float>, T>(value);
+            if (!stops) {
+                return stops.error();
+            }
 
-            if (!isArray(stopValue)) {
-                return Error { "function stop must be an array" };
+            auto base = 1.0f;
+            auto baseValue = objectMember(value, "base");
+            if (baseValue && toNumber(*baseValue)) {
+                base = *toNumber(*baseValue);
             }
 
-            if (arrayLength(stopValue) != 2) {
-                return Error { "function stop must have two elements" };
+            std::map<float, ExponentialStops<T>> convertedStops;
+            for (const auto& stop : *stops) {
+                auto& inner = convertedStops[stop.first.first];
+                inner.base = base;
+                inner.stops.emplace(stop.first.second, stop.second);
             }
 
-            optional<float> z = toNumber(arrayMember(stopValue, 0));
-            if (!z) {
-                return Error { "function stop zoom level must be a number" };
+            return CompositeFunction<T>(*propertyString, convertedStops);
+        } else if (type == "interval") {
+            auto stops = convertStops<CompositeValue<float>, T>(value);
+            if (!stops) {
+                return stops.error();
             }
 
-            Result<T> v = convert<T>(arrayMember(stopValue, 1));
-            if (!v) {
-                return v.error();
+            std::map<float, IntervalStops<T>> convertedStops;
+            for (const auto& stop : *stops) {
+                auto& inner = convertedStops[stop.first.first];
+                inner.stops.emplace(stop.first.second, stop.second);
             }
 
-            stops.emplace_back(*z, *v);
-        }
+            return CompositeFunction<T>(*propertyString, convertedStops);
+        } else if (type == "categorical") {
+            auto stops = convertStops<CompositeValue<CategoricalValue>, T>(value);
+            if (!stops) {
+                return stops.error();
+            }
 
-        auto baseValue = objectMember(value, "base");
-        if (!baseValue) {
-            return Function<T>(stops, 1.0f);
-        }
+            std::map<float, CategoricalStops<T>> convertedStops;
+            for (const auto& stop : *stops) {
+                auto& inner = convertedStops[stop.first.first];
+                inner.stops.emplace(stop.first.second, stop.second);
+            }
 
-        optional<float> base = toNumber(*baseValue);
-        if (!base) {
-            return Error { "function base must be a number"};
+            return CompositeFunction<T>(*propertyString, convertedStops);
+        } else {
+            return Error { "unsupported function type" };
         }
-
-        return Function<T>(stops, *base);
     }
 };
 
diff --git a/include/mbgl/style/conversion/property_setter.hpp b/include/mbgl/style/conversion/property_setter.hpp
index 1a601c7c1b..52fb160fde 100644
--- a/include/mbgl/style/conversion/property_setter.hpp
+++ b/include/mbgl/style/conversion/property_setter.hpp
@@ -4,6 +4,7 @@
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/constant.hpp>
 #include <mbgl/style/conversion/property_value.hpp>
+#include <mbgl/style/conversion/data_driven_property_value.hpp>
 
 #include <functional>
 #include <string>
@@ -18,15 +19,15 @@ using LayoutPropertySetter = std::function<optional<Error> (Layer&, const V&)>;
 template <class V>
 using PaintPropertySetter = std::function<optional<Error> (Layer&, const V&, const optional<std::string>&)>;
 
-template <class V, class L, class T, class...Args>
-auto makePropertySetter(void (L::*setter)(PropertyValue<T>, const Args&...args)) {
+template <class V, class L, class PropertyValue, class...Args>
+auto makePropertySetter(void (L::*setter)(PropertyValue, const Args&...args)) {
     return [setter] (Layer& layer, const V& value, const Args&...args) -> optional<Error> {
         L* typedLayer = layer.as<L>();
         if (!typedLayer) {
             return Error { "layer doesn't support this property" };
         }
 
-        Result<PropertyValue<T>> typedValue = convert<PropertyValue<T>>(value);
+        Result<PropertyValue> typedValue = convert<PropertyValue>(value);
         if (!typedValue) {
             return typedValue.error();
         }
diff --git a/include/mbgl/style/conversion/property_value.hpp b/include/mbgl/style/conversion/property_value.hpp
index de95b56155..d5e2a5c3c8 100644
--- a/include/mbgl/style/conversion/property_value.hpp
+++ b/include/mbgl/style/conversion/property_value.hpp
@@ -16,7 +16,7 @@ struct Converter<PropertyValue<T>> {
         if (isUndefined(value)) {
             return {};
         } else if (isObject(value)) {
-            Result<Function<T>> function = convert<Function<T>>(value);
+            Result<CameraFunction<T>> function = convert<CameraFunction<T>>(value);
             if (!function) {
                 return function.error();
             }