Constraint data and ragdoll atoms

A joint between two bodies is an hknpConstraintCinfo (the two body indices, a name, the constraint’s group) that points to a constraint data object. The data holds the joint’s rules as atoms: small classes, each starting with a 16-bit type word that names the rule (a pair of local frames, a limit, a motor, a friction). Characters carry their ragdolls this way (chr/c####.chrbnd), and so do parts, objects and assets that move on joints.

Every hknpConstraintCinfo of the character, parts, object, asset and map collision binders of both installs points to one of the classes below. Proven · every constraint of both installs

Class	Sekiro	Elden Ring	Elden Ring’s DLC pair
hkpRagdollConstraintData	2,031	5,739	3,146
hkpLimitedHingeConstraintData	439	1,260	478
hkpHingeConstraintData	26	1	0
hkpBallAndSocketConstraintData	0	681	101
hkpFixedConstraintData	0	36	14
hkpWheelConstraintData	0	48	0
hknpBreakableConstraintData	3	169	110

The counts are objects, each tagfile counted as often as a binder repeats it; the Elden Ring column is the base game’s archive pairs (Data1 and Data3 hold constraints), the last the expansion’s DLC pair. The base game’s counts are given alike by a reader that decodes the constraint classes and by a walk over the tagfiles’ type tables that shares no code with it; the DLC pair’s are the walk’s, and the class reader reads the same 11,783 Elden Ring objects in all. Proven · every constraint of both installs, the DLC pair included A breakable constraint wraps one of the others and adds a threshold: a ragdoll joint in all 3 Sekiro cases, in 152 of the 169 Elden Ring ones and 93 of the 110 in the DLC pair, a limited hinge in 16 of each Elden Ring set and a ball and socket joint in 1 of each. Proven · every constraint of both installs, the DLC pair included

Atoms

The members of the data’s atoms object are the atoms, each named after its role. The type word of an atom is the same in every object of a class, and the same in both games for the atoms they share. Proven · every constraint of both installs

Atom class	type	Members
hkpSetLocalTransformsConstraintAtom	2	transformA, transformB (an hkTransform each: 16 floats)
hkpSetLocalTranslationsConstraintAtom	3	translationA, translationB (a vector each)
hkpSetLocalRotationsConstraintAtom	4	rotationA, rotationB (an hkRotation each: 12 floats)
hkpBallSocketConstraintAtom	5	solvingMethod, bodiesToNotify, velocityStabilizationFactor (an hkUFloat8), enableLinearImpulseLimit, breachImpulse, inertiaStabilizationFactor
hkpLinConstraintAtom	7	axisIndex
hkpLinSoftConstraintAtom	8	axisIndex, tau, damping
hkpLinLimitConstraintAtom	9	axisIndex, min, max
hkp2dAngConstraintAtom	12	freeRotationAxis
hkpAngLimitConstraintAtom	14	isEnabled, limitAxis, cosineAxis, minAngle, maxAngle, angularLimitsTauFactor, angularLimitsDampFactor
hkpTwistLimitConstraintAtom	15	isEnabled, twistAxis, refAxis, minAngle, maxAngle, angularLimitsTauFactor, angularLimitsDampFactor
hkpConeLimitConstraintAtom	16	isEnabled, twistAxisInA, refAxisInB, angleMeasurementMode, memOffsetToAngleOffset, minAngle, maxAngle, angularLimitsTauFactor, angularLimitsDampFactor
hkpAngFrictionConstraintAtom	17	isEnabled, firstFrictionAxis, numFrictionAxes, maxFrictionTorque
hkpAngMotorConstraintAtom	18	isEnabled, motorAxis, targetAngle, motor (a pointer), two scratch offsets
hkpRagdollMotorConstraintAtom	19	isEnabled, target_bRca (an hkMatrix3: 12 floats), motors (three pointers), two scratch offsets
hkpSetupStabilizationAtom	23	enabled, maxLinImpulse, maxAngImpulse, maxAngle
hkp3dAngConstraintAtom	24	none

Proven · every constraint of both installs

Each class stores its atoms in a fixed order, under fixed names:

Class	Atoms (member name, type)
hkpRagdollConstraintData	transforms 2, setupStabilization 23, ragdollMotors 19, angFriction 17, twistLimit 15, coneLimit 16, planesLimit 16, ballSocket 5
hkpLimitedHingeConstraintData	transforms 2, setupStabilization 23, angMotor 18, angFriction 17, angLimit 14, 2dAng 12, ballSocket 5
hkpHingeConstraintData	transforms 2, setupStabilization 23, 2dAng 12, ballSocket 5
hkpBallAndSocketConstraintData	pivots 3, setupStabilization 23, ballSocket 5
hkpFixedConstraintData	transforms 2, setupStabilization 23, ballSocket 5, ang 24
hkpWheelConstraintData	suspensionBase 2, lin0Limit 9, lin0Soft 8, lin1 7, lin2 7, steeringBase 4, 2dAng 12; beside the atoms initialAxleInB and initialSteeringAxisInB (vectors)
hknpBreakableConstraintData	no atoms: constraintData (the wrapped object) and threshold

Proven · every constraint of both installs

The Havok 7.1 ragdoll data of Tony Hawk’s SHRED holds the same ragdoll atoms without setupStabilization: the types 2, 19, 17, 15, 16, 16 and 5. Observed · Sekiro, Elden Ring

Values

The transforms: an hkTransform is three rotation columns of four floats (x, y, z and a padding lane) and a translation of four. The rotation is orthonormal (the largest error of a column’s length or of two columns’ dot product is 1.2 × 10⁻⁶) and right-handed in every stored transform but one. The padding lanes are not initialised: they are 0 in a minority of the transforms and arbitrary in the others, and the translation’s padding lane likewise. Proven · every constraint of both installs The one exception is in the DLC pair: of its 7,494 transforms, the transformB of the ragdoll joint at index 12 of item 23 of c5320.hkx (in chr/c5320.chrbnd.dcx) holds a quiet NaN (0xFFC00000) in all twelve lanes of its rotation, padding included; its translation is finite. Proven · Elden Ring · every constraint of both installs, the DLC pair included

The integer members are constant per class in both games, wrapped or not, and the DLC pair’s take the same values:

• isEnabled is 1 for the friction, twist, cone, planes and angle limits and 0 for the two motor atoms.
• setupStabilization.enabled is 1 for every constraint that is not wrapped in a breakable one and 0 for every wrapped one.
• ballSocket.velocityStabilizationFactor is 48, bodiesToNotify and enableLinearImpulseLimit are 0, and solvingMethod is 0, but 1 in every wrapped constraint.
• The axes are fixed per slot: a ragdoll’s twistLimit has twistAxis 0 and refAxis 1, its coneLimit has twistAxisInA 0, refAxisInB 0, angleMeasurementMode 0 and memOffsetToAngleOffset 160, its planesLimit has 0, 1, 1 and 0, and its friction frees 3 axes from axis 0; a limited hinge’s angLimit has limitAxis 0 and cosineAxis 1 and its friction 1 axis from axis 0.
• A wheel’s lin0Limit and lin0Soft are on axis 0, lin1 on 1 and lin2 on 2.

Proven · every constraint of both installs

Every minAngle is at most its maxAngle (twist, cone, planes and hinge limits), the 10,211 limits of the DLC pair among them, and no float of any constraint is infinite. Proven · every constraint of both installs, the DLC pair included setupStabilization stores the largest finite floats and about 1.8 × 10¹⁹ for maxAngle. Proven · every constraint of both installs Only one constraint holds a float that is not a number, none in Sekiro or the base game’s pairs: the c5320 ragdoll joint above, whose transformB rotation and whole ragdollMotors.target_bRca (all twelve lanes) are 0xFFC00000; every other float of it is finite. Proven · every constraint of both installs, the DLC pair included

Does the game ever simulate the c5320 joint with NaN frames?

A ragdoll joint whose frame in body B and motor target are not numbers cannot be solved as stored. Whether c5320’s ragdoll is ever made active (its character’s ragdoll settings, or the engine replacing such a frame) is not established.

The motors are hkpPositionConstraintMotor objects (type, minForce, maxForce, tau, damping, proportionalRecoveryVelocity, constantRecoveryVelocity). A ragdoll’s three motor pointers are all set in 1,961 of Sekiro’s 2,031 unwrapped ragdoll joints and 5,715 of Elden Ring’s 5,739, and all null in the others and in every wrapped joint; a limited hinge’s pointer is set in 395 of Sekiro’s 439 and in all 1,260 of Elden Ring’s, and null in the wrapped ones. Proven · every constraint of both installs