1 files changed, 40 insertions, 0 deletions
diff --git a/src/mbgl/renderer/cross_faded_property_evaluator.cpp b/src/mbgl/renderer/cross_faded_property_evaluator.cpp
new file mode 100644
index 0000000000..ee3c86614f
--- /dev/null
+++ b/src/mbgl/renderer/cross_faded_property_evaluator.cpp
@@ -0,0 +1,40 @@
+#include <mbgl/renderer/cross_faded_property_evaluator.hpp>
+#include <mbgl/util/chrono.hpp>
+
+#include <cmath>
+
+namespace mbgl {
+
+template <typename T>
+Faded<T> CrossFadedPropertyEvaluator<T>::operator()(const style::Undefined&) const {
+    return calculate(defaultValue, defaultValue, defaultValue);
+}
+
+template <typename T>
+Faded<T> CrossFadedPropertyEvaluator<T>::operator()(const T& constant) const {
+    return calculate(constant, constant, constant);
+}
+
+template <typename T>
+Faded<T> CrossFadedPropertyEvaluator<T>::operator()(const style::CameraFunction<T>& function) const {
+    return calculate(function.evaluate(parameters.z - 1.0f),
+                     function.evaluate(parameters.z),
+                     function.evaluate(parameters.z + 1.0f));
+}
+
+template <typename T>
+Faded<T> CrossFadedPropertyEvaluator<T>::calculate(const T& min, const T& mid, const T& max) const {
+    const float z = parameters.z;
+    const float fraction = z - std::floor(z);
+    const std::chrono::duration<float> d = parameters.defaultFadeDuration;
+    const float t = std::min((parameters.now - parameters.zoomHistory.lastIntegerZoomTime) / d, 1.0f);
+
+    return z > parameters.zoomHistory.lastIntegerZoom
+        ? Faded<T> { min, mid, 2.0f, 1.0f, fraction + (1.0f - fraction) * t }
+        : Faded<T> { max, mid, 0.5f, 1.0f, 1 - (1 - t) * fraction };
+}
+
+template class CrossFadedPropertyEvaluator<std::string>;
+template class CrossFadedPropertyEvaluator<std::vector<float>>;
+
+} // namespace mbgl