VehicleEngine.h

// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT

#pragma once

#include <Jolt/ObjectStream/SerializableObject.h>
#include <Jolt/Core/LinearCurve.h>
#include <Jolt/Core/StreamIn.h>
#include <Jolt/Core/StreamOut.h>
#include <Jolt/Physics/StateRecorder.h>

JPH_NAMESPACE_BEGIN

#ifdef JPH_DEBUG_RENDERER
	class DebugRenderer;
#endif // JPH_DEBUG_RENDERER

/// Generic properties for a vehicle engine
class JPH_EXPORT VehicleEngineSettings
{
	JPH_DECLARE_SERIALIZABLE_NON_VIRTUAL(JPH_EXPORT, VehicleEngineSettings)

public:
	/// Constructor
							VehicleEngineSettings();

	/// Saves the contents in binary form to inStream.
	void					SaveBinaryState(StreamOut &inStream) const;

	/// Restores the contents in binary form to inStream.
	void					RestoreBinaryState(StreamIn &inStream);

	float					mMaxTorque = 500.0f;						///< Max amount of torque (Nm) that the engine can deliver
	float					mMinRPM = 1000.0f;							///< Min amount of revolutions per minute (rpm) the engine can produce without stalling
	float					mMaxRPM = 6000.0f;							///< Max amount of revolutions per minute (rpm) the engine can generate
	LinearCurve				mNormalizedTorque;							///< Y-axis: Curve that describes a ratio of the max torque the engine can produce (0 = 0, 1 = mMaxTorque). X-axis: the fraction of the RPM of the engine (0 = mMinRPM, 1 = mMaxRPM)
	float					mInertia = 0.5f;							///< Moment of inertia (kg m^2) of the engine
	float					mAngularDamping = 0.2f;						///< Angular damping factor of the wheel: dw/dt = -c * w
};

/// Runtime data for engine
class JPH_EXPORT VehicleEngine : public VehicleEngineSettings
{
public:
	/// Multiply an angular velocity (rad/s) with this value to get rounds per minute (RPM)
	static constexpr float	cAngularVelocityToRPM = 60.0f / (2.0f * JPH_PI);

	/// Clamp the RPM between min and max RPM
	inline void				ClampRPM()									{ mCurrentRPM = Clamp(mCurrentRPM, mMinRPM, mMaxRPM); }

	/// Current rotation speed of engine in rounds per minute
	float					GetCurrentRPM() const						{ return mCurrentRPM; }

	/// Update rotation speed of engine in rounds per minute
	void					SetCurrentRPM(float inRPM)					{ mCurrentRPM = inRPM; ClampRPM(); }

	/// Get current angular velocity of the engine in radians / second
	inline float			GetAngularVelocity() const					{ return mCurrentRPM / cAngularVelocityToRPM; }

	/// Get the amount of torque (N m) that the engine can supply
	/// @param inAcceleration How much the gas pedal is pressed [0, 1]
	float					GetTorque(float inAcceleration) const		{ return inAcceleration * mMaxTorque * mNormalizedTorque.GetValue(mCurrentRPM / mMaxRPM); }

	/// Apply a torque to the engine rotation speed
	/// @param inTorque Torque in N m
	/// @param inDeltaTime Delta time in seconds
	void					ApplyTorque(float inTorque, float inDeltaTime);

	/// Update the engine RPM for damping
	/// @param inDeltaTime Delta time in seconds
	void					ApplyDamping(float inDeltaTime);

#ifdef JPH_DEBUG_RENDERER
	// Function that converts RPM to an angle in radians for debugging purposes
	float					ConvertRPMToAngle(float inRPM) const		{ return (-0.75f + 1.5f * inRPM / mMaxRPM) * JPH_PI; }

	/// Debug draw a RPM meter
	void					DrawRPM(DebugRenderer *inRenderer, RVec3Arg inPosition, Vec3Arg inForward, Vec3Arg inUp, float inSize, float inShiftDownRPM, float inShiftUpRPM) const;
#endif // JPH_DEBUG_RENDERER

	/// If the engine is idle we allow the vehicle to sleep
	bool					AllowSleep() const							{ return mCurrentRPM <= 1.01f * mMinRPM; }

	/// Saving state for replay
	void					SaveState(StateRecorder &inStream) const;
	void					RestoreState(StateRecorder &inStream);

private:
	float					mCurrentRPM = mMinRPM;						///< Current rotation speed of engine in rounds per minute
};

JPH_NAMESPACE_END