Animation clips

An AnimationClip (class 74) of Mecanim (m_Legacy false) stores its curves in m_MuscleClip. Legacy clips store curves per kind and are a different layout (legacy clips). A clip’s curves are numbered across three blocks, in this order: the streamed curves (m_StreamedClip), the dense curves (m_DenseClip, one sample per frame at a fixed rate) and the constant curves (m_ConstantClip, one value each). Observed · SkateBIRD, Sledding

Bindings

m_ClipBindingConstant.genericBindings lists what the curves drive, in curve order. Each binding has:

Field	Meaning	Confidence
path	the CRC-32 (the zlib one) of the path of GameObject names below the Animator’s own GameObject; the Animator’s GameObject itself is the empty path, hash 0	Observed · SkateBIRD, Sledding
attribute	for a Transform (typeID 4): 1 position, 2 rotation (a quaternion), 3 scale, 4 Euler angles; for another class the hash of the property	Observed · SkateBIRD, Sledding
typeID	the target’s class id: 4 Transform, 95 Animator, 137 SkinnedMeshRenderer, …	Observed · SkateBIRD, Sledding
curve count	a binding takes one curve for a float property; for a Transform attribute 3 (position, scale, Euler) or 4 (rotation)	Observed · SkateBIRD, Sledding

The path hash is the CRC-32 of the target’s path; an avatar’s name table (m_TOS) maps hashes back to names. Observed · SkateBIRD A clip’s blend shape curve binds to a SkinnedMeshRenderer by its path hash and the shape’s name hash. Observed · Sledding

The streamed block

The streamed block is a sequence of frames. Each frame is a time (f32), a count (i32) and that many keys, each an index (i32, which curve) and four f32 coefficients. A key opens a cubic segment of its curve that lasts until the curve’s next key:

value(dt) = ((c0 · dt + c1) · dt + c2) · dt + c3 for dt seconds after the key,

so c3 is the key’s value and c2 its outgoing slope; the incoming slope of the next key is the derivative at the segment’s end. The first frame is at time −f32::MAX and gives every curve’s initial value; the last is at +∞ and has no keys. A segment whose coefficients are not finite is a step. Observed · SkateBIRD, Sledding The slopes are per second: scaling a slope by the segment length again would count the length twice. Observed · SkateBIRD

A curve with only its initial entry is constant. Frames that do not end at +∞ and times that go backwards are not valid streamed data. Observed

A key’s curve index can reach past the clip’s curve count. In PEAK (Unity 6000.3.15f1), 98 of the 740 clips of two level bundles (levels0-31 and levels192-207) have keys whose index is at or past the streamed block’s curveCount, in the first frame and in later ones, most with coefficients that are not zero; the other 642 keep every key below it. All 98 end at the +∞ frame. Observed · PEAK RespawnChest_Open (also in the loose sharedassets4.assets, so not an effect of the bundle) has a curveCount of 17, no dense curves and 17 generic bindings; its first frame keys indices 0 to 17, index 17 with all-zero coefficients, and its later frames 0 to 16. Observed · PEAK

What does a curve index past the count address?

Whether the extra indices of those 98 PEAK clips drive bindings past the streamed block or are a placeholder curve is not established.

Object curves

A binding whose isPPtrCurve is set drives an object reference (a renderer’s material, a sprite). It takes one curve like a float property, and the curve’s values are indices into m_ClipBindingConstant.pptrCurveMapping, the list of objects the clip swaps in. In Risk of Rain 2, 5 of its 4,898 Mecanim clips have such bindings (20 of them, all on a SkinnedMeshRenderer, class 137, attribute 0), their mappings name 28 objects, and every one of their 26 keys is a whole number that indexes the mapping; the bindings and mappings are the ones an independent type tree reader gives. Proven · RoR2 No binding of those clips or of Schedule I’s 279 sets isIntCurve or isSerializeReferenceCurve. Observed · RoR2, Schedule I

A clip’s length is m_StopTime − m_StartTime seconds. Its animation events (m_Events) are a separate list. Sourced · Unity scripting reference

Legacy clips

A legacy clip (m_Legacy true, played by the Animation component) keeps a default m_MuscleClip (no curves, m_StartTime 0 and m_StopTime 1) and no generic bindings; its curves are Unity’s own keyframe curves, stored by kind with the path of their target as text:

Field	Curve	Value of a key
m_RotationCurves	a Transform’s rotation	a quaternion (x y z w)
m_EulerCurves	a Transform’s Euler angles, with m_RotationOrder	three floats
m_PositionCurves, m_ScaleCurves	a Transform’s position and scale	three floats
m_FloatCurves	a property of a component: attribute (its name), classID, script	one float
m_PPtrCurves	an object property: attribute, classID, script	a PPtr
m_CompressedRotationCurves	rotation curves in a compressed form, with m_Compressed

Each curve is an AnimationCurve: m_Curve, a list of keyframes of time, value, inSlope and outSlope (from Unity 2018.1 also weightedMode, inWeight and outWeight), and m_PreInfinity, m_PostInfinity and m_RotationOrder. The clip’s wrap mode is m_WrapMode (0 default, 1 once, 2 loop, 4 ping-pong, 8 clamp forever). Sourced[Unity scripting reference]

Every legacy clip of Enter the Gungeon (27), Risk of Rain 2 (25) and Schedule I (187) reads in that layout, each key of each curve equal to an independent type tree reader’s. Proven · Gungeon, RoR2, Schedule I None of them is compressed or has object curves, every Euler curve is of rotation order 4 (Z, then X, then Y), and every pre- and post-infinity is 2 (clamp). Observed · Gungeon, RoR2, Schedule I The muscle clip’s stop time is not the clip’s length: 179 of Schedule I’s 187 legacy clips have keys past 1 s or end before it. Observed · Schedule I Two of Schedule I’s clips start at a first key later than 0. Observed · Schedule I Gungeon’s (Unity 2017.4) keyframes have no weightedMode. Observed · Gungeon One of Schedule I’s legacy clips wraps ping-pong (m_WrapMode 4): it plays forward, then backward. Proven · Schedule I

A legacy curve’s path names its target as a mechanim binding’s path hash does: its CRC-32 is the hash. Mecanim’s Transform attributes 1 to 4 are the position, rotation, scale and Euler kinds, and a float curve’s attribute names its property as a binding’s attribute hash does. Inferred

Tangents and weights

Between two keys a curve is a cubic Hermite spline of their values and their slopes (per second). A slope that is infinite on either side of a segment makes it a step: the segment holds the first key’s value. Sourced · Unity scripting reference weightedMode bit 1 (In) makes the key’s inWeight count and bit 2 (Out) its outWeight. A weighted side of a segment is the Bezier handle that fraction of the segment’s span from its key, along its slope; an unweighted side is a third, which is where the Hermite spline’s handles are. The segment is then the cubic Bezier curve in time and value of those handles, not a cubic in time. Sourced · Unity scripting reference Schedule I has 24 curves with weighted keys. Proven · Schedule I

Humanoid curves

A humanoid clip’s Animator binding (typeID 95) carries the root, the IK goals and the muscles; see humanoid muscles. Observed · Sledding

SkateBIRD

Checks against another decoder

Three clips of SkateBIRD’s bird, decoded by AssetStudio and by a reader of the layout above, then evaluated with Unity’s cubic Hermite rule between keys: Flapping (path id 1250 of sharedassets0.assets, 48 bindings, 160 curves), Grab Left Loop (1274; 90 bindings, 300 curves) and Bounce Dance Mood (1257; 12 bindings, 40 curves). The blocks hold exactly those curves, every binding matches a joint by the CRC-32 of its path, and the two decoders drive the same (joint, property) pairs. Constant curves agree to 5e-9. With the slopes read per second, the animated curves agree to 4.8e-6, 7e-4 and 2.3e-5 degrees (rotation). Observed · SkateBIRD

sharedassets5.assets holds another Flapping with 391 bindings for a different rig. Observed · SkateBIRD