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#pragma once
#include <mbgl/style/property_value.hpp>
#include <mbgl/style/data_driven_property_value.hpp>
#include <mbgl/style/transition_options.hpp>
#include <mbgl/util/interpolate.hpp>
#include <utility>
namespace mbgl {
namespace style {
template <class Value>
class TransitioningProperty {
public:
TransitioningProperty() = default;
TransitioningProperty(Value value_,
TransitioningProperty<Value> prior_,
TransitionOptions transition,
TimePoint now)
: begin(now + transition.delay.value_or(Duration::zero())),
end(begin + transition.duration.value_or(Duration::zero())),
value(std::move(value_)) {
if (transition.isDefined()) {
prior = { std::move(prior_) };
}
}
template <class Evaluator>
auto evaluate(const Evaluator& evaluator, TimePoint now) {
auto finalValue = value.evaluate(evaluator);
if (!prior) {
// No prior value.
return finalValue;
} else if (now >= end) {
// Transition from prior value is now complete.
prior = {};
return finalValue;
} else if (value.isDataDriven()) {
// Transitions to data-driven properties are not supported.
// We snap immediately to the data-driven value so that, when we perform layout,
// we see the data-driven function and can use it to populate vertex buffers.
prior = {};
return finalValue;
} else if (now < begin) {
// Transition hasn't started yet.
return prior->get().evaluate(evaluator, now);
} else {
// Interpolate between recursively-calculated prior value and final.
float t = std::chrono::duration<float>(now - begin) / (end - begin);
return util::interpolate(prior->get().evaluate(evaluator, now), finalValue,
util::DEFAULT_TRANSITION_EASE.solve(t, 0.001));
}
}
bool hasTransition() const {
return bool(prior);
}
bool isUndefined() const {
return value.isUndefined();
}
const Value& getValue() const {
return value;
}
private:
optional<mapbox::util::recursive_wrapper<TransitioningProperty<Value>>> prior;
TimePoint begin;
TimePoint end;
Value value;
};
} // namespace style
} // namespace mbgl
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