JoltPhysics/Jolt/Physics/Body/MotionProperties.inl

// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT

#pragma once

JPH_NAMESPACE_BEGIN

void MotionProperties::SetMassProperties(const MassProperties &inMassProperties)
{
	// Set inverse mass
	JPH_ASSERT(inMassProperties.mMass > 0.0f);
	mInvMass = 1.0f / inMassProperties.mMass;

	// Set inverse inertia
	Mat44 rotation;
	Vec3 diagonal;
	if (inMassProperties.DecomposePrincipalMomentsOfInertia(rotation, diagonal) 
		&& !diagonal.IsNearZero())
	{	
		mInvInertiaDiagonal = diagonal.Reciprocal();
		mInertiaRotation = rotation.GetQuaternion();
	}
	else
	{
		// Failed! Fall back to inertia tensor of sphere with radius 1.
		mInvInertiaDiagonal = Vec3::sReplicate(2.5f * mInvMass);
		mInertiaRotation = Quat::sIdentity();
	}
}

void MotionProperties::MoveKinematic(Vec3Arg inDeltaPosition, QuatArg inDeltaRotation, float inDeltaTime)
{
	JPH_ASSERT(BodyAccess::sCheckRights(BodyAccess::sVelocityAccess, BodyAccess::EAccess::ReadWrite)); 
	JPH_ASSERT(BodyAccess::sCheckRights(BodyAccess::sPositionAccess, BodyAccess::EAccess::Read)); 
	JPH_ASSERT(mCachedMotionType != EMotionType::Static);

	// Calculate required linear velocity
	mLinearVelocity = inDeltaPosition / inDeltaTime;

	// Calculate required angular velocity
	Vec3 axis;
	float angle;
	inDeltaRotation.GetAxisAngle(axis, angle);
	mAngularVelocity = axis * (angle / inDeltaTime);
}

void MotionProperties::ClampLinearVelocity()
{ 
	JPH_ASSERT(BodyAccess::sCheckRights(BodyAccess::sVelocityAccess, BodyAccess::EAccess::ReadWrite)); 

	float len_sq = mLinearVelocity.LengthSq(); 
	JPH_ASSERT(isfinite(len_sq)); 
	if (len_sq > Square(mMaxLinearVelocity)) 
		mLinearVelocity *= mMaxLinearVelocity / sqrt(len_sq); 
}

void MotionProperties::ClampAngularVelocity()
{ 
	JPH_ASSERT(BodyAccess::sCheckRights(BodyAccess::sVelocityAccess, BodyAccess::EAccess::ReadWrite)); 

	float len_sq = mAngularVelocity.LengthSq(); 
	JPH_ASSERT(isfinite(len_sq)); 
	if (len_sq > Square(mMaxAngularVelocity)) 
		mAngularVelocity *= mMaxAngularVelocity / sqrt(len_sq); 
}

inline Mat44 MotionProperties::GetLocalSpaceInverseInertiaUnchecked() const
{ 
	Mat44 rotation = Mat44::sRotation(mInertiaRotation);
	Mat44 rotation_mul_scale_transposed(mInvInertiaDiagonal.SplatX() * rotation.GetColumn4(0), mInvInertiaDiagonal.SplatY() * rotation.GetColumn4(1), mInvInertiaDiagonal.SplatZ() * rotation.GetColumn4(2), Vec4(0, 0, 0, 1));
	return rotation.Multiply3x3RightTransposed(rotation_mul_scale_transposed);
}

inline Mat44 MotionProperties::GetLocalSpaceInverseInertia() const
{
	JPH_ASSERT(mCachedMotionType == EMotionType::Dynamic);
	return GetLocalSpaceInverseInertiaUnchecked();
}

Mat44 MotionProperties::GetInverseInertiaForRotation(Mat44Arg inRotation) const
{ 
	JPH_ASSERT(mCachedMotionType == EMotionType::Dynamic);

	Mat44 rotation = inRotation * Mat44::sRotation(mInertiaRotation); 
	Mat44 rotation_mul_scale_transposed(mInvInertiaDiagonal.SplatX() * rotation.GetColumn4(0), mInvInertiaDiagonal.SplatY() * rotation.GetColumn4(1), mInvInertiaDiagonal.SplatZ() * rotation.GetColumn4(2), Vec4(0, 0, 0, 1));
	return rotation.Multiply3x3RightTransposed(rotation_mul_scale_transposed);
}

Vec3 MotionProperties::MultiplyWorldSpaceInverseInertiaByVector(QuatArg inBodyRotation, Vec3Arg inV) const
{ 
	JPH_ASSERT(mCachedMotionType == EMotionType::Dynamic);

	Mat44 rotation = Mat44::sRotation(inBodyRotation * mInertiaRotation); 
	return rotation.Multiply3x3(mInvInertiaDiagonal * rotation.Multiply3x3Transposed(inV)); 
}

void MotionProperties::ApplyForceTorqueAndDragInternal(QuatArg inBodyRotation, Vec3Arg inGravity, float inDeltaTime)
{
	JPH_ASSERT(BodyAccess::sCheckRights(BodyAccess::sVelocityAccess, BodyAccess::EAccess::ReadWrite)); 
	JPH_ASSERT(mCachedMotionType == EMotionType::Dynamic);

	// Update linear velocity
	mLinearVelocity += inDeltaTime * (mGravityFactor * inGravity + mInvMass * Vec3::sLoadFloat3Unsafe(mForce));

	// Update angular velocity
	mAngularVelocity += inDeltaTime * MultiplyWorldSpaceInverseInertiaByVector(inBodyRotation, Vec3::sLoadFloat3Unsafe(mTorque));

	// Linear damping: dv/dt = -c * v
	// Solution: v(t) = v(0) * e^(-c * t) or v2 = v1 * e^(-c * dt)
	// Taylor expansion of e^(-c * dt) = 1 - c * dt + ...
	// Since dt is usually in the order of 1/60 and c is a low number too this approximation is good enough
	mLinearVelocity *= max(0.0f, 1.0f - mLinearDamping * inDeltaTime);
	mAngularVelocity *= max(0.0f, 1.0f - mAngularDamping * inDeltaTime);

	// Clamp velocities
	ClampLinearVelocity();
	ClampAngularVelocity();
}

void MotionProperties::ResetSleepTestSpheres(const Vec3 *inPoints)
{
	for (int i = 0; i < 3; ++i)
		mSleepTestSpheres[i] = Sphere(inPoints[i], 0.0f);
	mSleepTestTimer = 0.0f;
}

JPH_NAMESPACE_END