1 files changed, 52 insertions, 8 deletions
diff --git a/include/mbgl/style/function/camera_function.hpp b/include/mbgl/style/function/camera_function.hpp
index 0fd5bcb078..25b38e3616 100644
--- a/include/mbgl/style/function/camera_function.hpp
+++ b/include/mbgl/style/function/camera_function.hpp
@@ -1,10 +1,18 @@
 #pragma once
 
+#include <mbgl/style/expression/expression.hpp>
+#include <mbgl/style/expression/interpolate.hpp>
+#include <mbgl/style/expression/step.hpp>
+#include <mbgl/style/expression/find_zoom_curve.hpp>
+#include <mbgl/style/expression/value.hpp>
+#include <mbgl/style/expression/is_constant.hpp>
+#include <mbgl/style/function/convert.hpp>
 #include <mbgl/style/function/exponential_stops.hpp>
 #include <mbgl/style/function/interval_stops.hpp>
 #include <mbgl/util/interpolate.hpp>
 #include <mbgl/util/variant.hpp>
 
+
 namespace mbgl {
 namespace style {
 
@@ -12,30 +20,66 @@ template <class T>
 class CameraFunction {
 public:
     using Stops = std::conditional_t<
-        util::Interpolatable<T>,
+        util::Interpolatable<T>::value,
         variant<
             ExponentialStops<T>,
             IntervalStops<T>>,
         variant<
             IntervalStops<T>>>;
+    
+    CameraFunction(std::unique_ptr<expression::Expression> expression_)
+         : expression(std::move(expression_)),
+           zoomCurve(expression::findZoomCurveChecked(expression.get()))
+    {
+        assert(!expression::isZoomConstant(*expression));
+        assert(expression::isFeatureConstant(*expression));
+    }
 
     CameraFunction(Stops stops_)
-        : stops(std::move(stops_)) {
-    }
+        : stops(std::move(stops_)),
+          expression(stops.match([&] (const auto& s) {
+            return expression::Convert::toExpression(s);
+          })),
+          zoomCurve(expression::findZoomCurveChecked(expression.get()))
+    {}
 
     T evaluate(float zoom) const {
-        return stops.match([&] (const auto& s) {
-            return s.evaluate(zoom).value_or(T());
-        });
+        const expression::EvaluationResult result = expression->evaluate(expression::EvaluationContext(zoom, nullptr));
+        if (result) {
+           const optional<T> typed = expression::fromExpressionValue<T>(*result);
+           return typed ? *typed : T();
+        }
+        return T();
+    }
+    
+    float interpolationFactor(const Range<float>& inputLevels, const float inputValue) const {
+        return zoomCurve.match(
+            [&](const expression::InterpolateBase* z) {
+                return z->interpolationFactor(Range<double> { inputLevels.min, inputLevels.max }, inputValue);
+            },
+            [&](const expression::Step*) { return 0.0f; }
+        );
+    }
+    
+    Range<float> getCoveringStops(const float lower, const float upper) const {
+        return zoomCurve.match(
+            [&](auto z) { return z->getCoveringStops(lower, upper); }
+        );
     }
     
     friend bool operator==(const CameraFunction& lhs,
                            const CameraFunction& rhs) {
-        return lhs.stops == rhs.stops;
+        return *lhs.expression == *rhs.expression;
     }
 
-    Stops stops;
     bool useIntegerZoom = false;
+    
+    // retained for compatibility with pre-expression function API
+    Stops stops;
+
+private:
+    std::shared_ptr<expression::Expression> expression;
+    const variant<const expression::InterpolateBase*, const expression::Step*> zoomCurve;
 };
 
 } // namespace style