MotionProperties.inl

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// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT
 
#pragma once
 
JPH_NAMESPACE_BEGIN
 
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(mCachedBodyType == EBodyType::RigidBody);
    JPH_ASSERT(mCachedMotionType != EMotionType::Static);
 
    // Calculate required linear velocity
    mLinearVelocity = LockTranslation(inDeltaPosition / inDeltaTime);
 
    // Calculate required angular velocity
    mAngularVelocity = LockAngular(inDeltaRotation.GetAngularVelocity(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 void MotionProperties::ScaleToMass(float inMass)
{
    JPH_ASSERT(mInvMass > 0.0f, "Body must have finite mass");
    JPH_ASSERT(inMass > 0.0f, "New mass cannot be zero");
 
    float new_inv_mass = 1.0f / inMass;
    mInvInertiaDiagonal *= new_inv_mass / mInvMass;
    mInvMass = new_inv_mass;
}
 
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.Multiply3x3(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));
    Mat44 inverse_inertia = rotation.Multiply3x3RightTransposed(rotation_mul_scale_transposed);
 
    // We need to mask out both the rows and columns of DOFs that are not allowed
    Vec4 angular_dofs_mask = GetAngularDOFsMask().ReinterpretAsFloat();
    inverse_inertia.SetColumn4(0, Vec4::sAnd(inverse_inertia.GetColumn4(0), Vec4::sAnd(angular_dofs_mask, angular_dofs_mask.SplatX())));
    inverse_inertia.SetColumn4(1, Vec4::sAnd(inverse_inertia.GetColumn4(1), Vec4::sAnd(angular_dofs_mask, angular_dofs_mask.SplatY())));
    inverse_inertia.SetColumn4(2, Vec4::sAnd(inverse_inertia.GetColumn4(2), Vec4::sAnd(angular_dofs_mask, angular_dofs_mask.SplatZ())));
 
    return inverse_inertia;
}
 
Vec3 MotionProperties::MultiplyWorldSpaceInverseInertiaByVector(QuatArg inBodyRotation, Vec3Arg inV) const
{
    JPH_ASSERT(mCachedMotionType == EMotionType::Dynamic);
 
    // Mask out columns of DOFs that are not allowed
    Vec3 angular_dofs_mask = Vec3(GetAngularDOFsMask().ReinterpretAsFloat());
    Vec3 v = Vec3::sAnd(inV, angular_dofs_mask);
 
    // Multiply vector by inverse inertia
    Mat44 rotation = Mat44::sRotation(inBodyRotation * mInertiaRotation);
    Vec3 result = rotation.Multiply3x3(mInvInertiaDiagonal * rotation.Multiply3x3Transposed(v));
 
    // Mask out rows of DOFs that are not allowed
    return Vec3::sAnd(result, angular_dofs_mask);
}
 
void MotionProperties::ApplyGyroscopicForceInternal(QuatArg inBodyRotation, float inDeltaTime)
{
    JPH_ASSERT(BodyAccess::sCheckRights(BodyAccess::sVelocityAccess(), BodyAccess::EAccess::ReadWrite));
    JPH_ASSERT(mCachedBodyType == EBodyType::RigidBody);
    JPH_ASSERT(mCachedMotionType == EMotionType::Dynamic);
 
    // Calculate local space inertia tensor (a diagonal in local space)
    UVec4 is_zero = Vec3::sEquals(mInvInertiaDiagonal, Vec3::sZero());
    Vec3 denominator = Vec3::sSelect(mInvInertiaDiagonal, Vec3::sOne(), is_zero);
    Vec3 nominator = Vec3::sSelect(Vec3::sOne(), Vec3::sZero(), is_zero);
    Vec3 local_inertia = nominator / denominator; // Avoid dividing by zero, inertia in this axis will be zero
 
    // Calculate local space angular momentum
    Quat inertia_space_to_world_space = inBodyRotation * mInertiaRotation;
    Vec3 local_angular_velocity = inertia_space_to_world_space.InverseRotate(mAngularVelocity);
    Vec3 local_momentum = local_inertia * local_angular_velocity;
 
    // The gyroscopic force applies a torque: T = -w x I w where w is angular velocity and I the inertia tensor
    // Calculate the new angular momentum by applying the gyroscopic force and make sure the new magnitude is the same as the old one
    // to avoid introducing energy into the system due to the Euler step
    Vec3 new_local_momentum = local_momentum - inDeltaTime * local_angular_velocity.Cross(local_momentum);
    float new_local_momentum_len_sq = new_local_momentum.LengthSq();
    new_local_momentum = new_local_momentum_len_sq > 0.0f? new_local_momentum * sqrt(local_momentum.LengthSq() / new_local_momentum_len_sq) : Vec3::sZero();
 
    // Convert back to world space angular velocity
    mAngularVelocity = inertia_space_to_world_space * (mInvInertiaDiagonal * new_local_momentum);
}
 
void MotionProperties::ApplyForceTorqueAndDragInternal(QuatArg inBodyRotation, Vec3Arg inGravity, float inDeltaTime)
{
    JPH_ASSERT(BodyAccess::sCheckRights(BodyAccess::sVelocityAccess(), BodyAccess::EAccess::ReadWrite));
    JPH_ASSERT(mCachedBodyType == EBodyType::RigidBody);
    JPH_ASSERT(mCachedMotionType == EMotionType::Dynamic);
 
    // Update linear velocity
    mLinearVelocity = LockTranslation(mLinearVelocity + inDeltaTime * (mGravityFactor * inGravity + mInvMass * GetAccumulatedForce()));
 
    // Update angular velocity
    mAngularVelocity += inDeltaTime * MultiplyWorldSpaceInverseInertiaByVector(inBodyRotation, GetAccumulatedTorque());
 
    // 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 RVec3 *inPoints)
{
#ifdef JPH_DOUBLE_PRECISION
    // Make spheres relative to the first point and initialize them to zero radius
    DVec3 offset = inPoints[0];
    offset.StoreDouble3(&mSleepTestOffset);
    mSleepTestSpheres[0] = Sphere(Vec3::sZero(), 0.0f);
    for (int i = 1; i < 3; ++i)
        mSleepTestSpheres[i] = Sphere(Vec3(inPoints[i] - offset), 0.0f);
#else
    // Initialize the spheres to zero radius around the supplied points
    for (int i = 0; i < 3; ++i)
        mSleepTestSpheres[i] = Sphere(inPoints[i], 0.0f);
#endif
 
    mSleepTestTimer = 0.0f;
}
 
ECanSleep MotionProperties::AccumulateSleepTime(float inDeltaTime, float inTimeBeforeSleep)
{
    mSleepTestTimer += inDeltaTime;
    return mSleepTestTimer >= inTimeBeforeSleep? ECanSleep::CanSleep : ECanSleep::CannotSleep;
}
 
JPH_NAMESPACE_END