interpolated_property.h

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/*  interpolated_property.h                                               */
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#pragma once

struct Vector2;

namespace InterpolatedPropertyFuncs {
float lerp(float p_a, float p_b, float p_fraction);
double lerp(double p_a, double p_b, float p_fraction);
Vector2 lerp(const Vector2 &p_a, const Vector2 &p_b, float p_fraction);
} //namespace InterpolatedPropertyFuncs

// This class is intended to reduce the boiler plate involved to
// support custom properties to be physics interpolated.

template <class T>
class InterpolatedProperty {
	// Only needs interpolating / updating the servers when
	// curr and prev are different.
	bool _needs_interpolating = false;
	T _interpolated;
	T curr;
	T prev;

public:
	// FTI depends on the constant flow between current values
	// (on the current tick) and stored previous values (on the previous tick).
	// These should be updated both on each tick, and also on resets.
	void pump() {
		prev = curr;
		_needs_interpolating = false;
	}
	void reset() { pump(); }

	void set_interpolated_value(const T &p_val) {
		_interpolated = p_val;
	}
	const T &interpolated() const { return _interpolated; }
	bool needs_interpolating() const { return _needs_interpolating; }

	bool interpolate(float p_interpolation_fraction) {
		if (_needs_interpolating) {
			_interpolated = InterpolatedPropertyFuncs::lerp(prev, curr, p_interpolation_fraction);
			return true;
		}
		return false;
	}

	operator T() const {
		return curr;
	}

	bool operator==(const T &p_o) const {
		return p_o == curr;
	}

	bool operator!=(const T &p_o) const {
		return p_o != curr;
	}

	InterpolatedProperty &operator=(T p_val) {
		curr = p_val;
		_interpolated = p_val;
		_needs_interpolating = true;
		return *this;
	}
	InterpolatedProperty(T p_val) {
		curr = p_val;
		_interpolated = p_val;
		pump();
	}
	InterpolatedProperty() {
		// Ensure either the constructor is run,
		// or the memory is zeroed if using a fundamental type.
		_interpolated = T{};
		curr = T{};
		prev = T{};
	}
};