Squash & Stretch

Public type: UOverAnimSquashStretchModule
Header: OverAnimation/Asset/OverAnimModule.h
Execution Phase: Shape

Purpose

Squash & Stretch is a Shape module that deforms a Bone Group's primary-axis length and cross-section in response to Signals. With a Span, it calculates length, silhouette, and attachment propagation between two endpoints. Without a Span, it deforms Region shape around a pivot and axis.

Details properties

Module ID, Module Name, Enabled, and Order Within Module Phase are hidden by Details customization. Input Composition is an inherited property exposed in Details.

Optional Span (OverAnim | Span)

Details customization shows the following authoring tool and status above the properties. Neither is a serialized C++ property.

UI	Behavior
Auto Configure	Finds a connected primary chain among the selected Bone Group's explicit Affected Bones, fills Span Start and Span End, and adds existing Regions branching from either endpoint to Attachment Targets. It does not create or rename Bone Groups. If a span or attachments already exist, it asks before overwriting them.
Shape Scope	Shows Anatomical Span when both endpoints exist, Incomplete Span when only one exists, and Local Region when neither exists.

Auto Configure requires at least two explicit Affected Bones connected in the same parent-child chain in the Target Skeleton. Bones included only through hierarchy expansion are not primary-span candidates.

UI name	C++ property	Default · unit · range	Visibility · effect
Span Start	SpanStartBone	None	First bone of the anatomical length interval. Span propagation is enabled only with Span End. If only one endpoint is present, an Automatic Six-Stage Motion Response cannot be created.
Span End	SpanEndBone	None	Last bone of the interval. It must be an ancestor or descendant of Span Start and lie in the same Region. If runtime cannot find both endpoint control points, no effect is created.
Anchor Policy	AnchorPolicy	Keep Start Fixed	Shown with a Span. Selects the span pivot from Keep Start Fixed, Keep End Fixed, Split From Center, or Keep Contact Fixed. Keep Contact Fixed requires a valid Signal contact point.
Silhouette Profile	SpanProfileMode	Smooth Silhouette (Recommended)	Shown with a Span. Selects the transition profile for span length and cross-section from Uniform Scale (Legacy), Tapered Linear, Smooth Silhouette (Recommended), or Custom Silhouette.
Profile Sharpness	SpanProfileExponent	1.0, 0.1–8.0	Shown when Silhouette Profile = Custom Silhouette. Exponent of the custom profile.
Silhouette Balance	SilhouetteBalance	Balanced	Shown with a Span. Places span cross-section emphasis as Balanced, Emphasize Span Start, or Emphasize Span End.
Balance Strength	SilhouetteBalanceStrength	0.4, 0–0.8	Shown when Silhouette Balance != Balanced. Amount of Start/End profile bias.
Attachment Targets	AttachmentTargets	Empty array	Shown with a Span. References that propagate endpoint translation to other Regions. This list does not add target Regions to the source module's shape mask.

An Incomplete Span with only one endpoint is a validation error. In Local Region, a warning says stored Attachment Targets are inactive.

Each FOverAnimSquashAttachmentTarget item in Attachment Targets is shown in this order.

UI name	C++ property	Default · unit · range	Visibility · effect
Dependent Region	BoneGroupName	None	Name of the propagation target Bone Group. No attachment edge is created if the name is empty or Overall Weight is nearly zero.
Endpoint	Endpoint	End Endpoint	Selects translation from the source span's Start Endpoint or End Endpoint.
Overall Weight	PropagationWeight	1.0, 0–1	Overall endpoint-translation weight applied to the target Region.
Propagation Profile	FalloffMode	Uniform	Uniform moves the target Region like one attached mass; Chain Distance calculates per-bone weights from target Region root to tip.
Root Weight	RootWeight	1.0, 0–1	Shown when Propagation Profile = Chain Distance. Propagation weight at target Region chain root.
Tip Weight	TipWeight	0.0, 0–1	Shown when Propagation Profile = Chain Distance. Propagation weight at target Region chain tip.
Distance Exponent	FalloffExponent	1.0, 0.1–8.0	Shown when Propagation Profile = Chain Distance. Exponent of the root-to-tip falloff profile.

OverAnim | Shape

UI name	C++ property	Default · unit · range	Visibility · effect
Pivot Bone	PivotBone	None	Shown when Pivot Mode = Region Bone or Skeleton Bone. Hidden with Pivot Mode when using a Span. Region Bone finds the pivot in current control points; Skeleton Bone prefers reference control points.
Pivot Mode	PivotMode	Auto	Shown without a Span. Region Bone/Skeleton Bone use Pivot Bone; Signal Origin uses OriginWS; Contact Point uses ContactPointWS. Auto uses the first valid control point.
Prevent Contact Penetration	bUseContactPlane	true	Applies a contact plane only when the Signal contains both valid contact point and normal. Without a Span, anchors shape to the plane; with a Span, also anchors when Anchor Policy = Keep Contact Fixed. Missing contact data does not by itself reject a request.
Axis Mode	AxisMode	LocalZ	Sets primary axis without a Span. LocalX/Y/Z use pivot-transform axes; Signal Direction uses DirectionWS; Contact Normal uses ContactNormalWS. With a Span, the endpoint position difference is the axis and this value is unused for primary-axis calculation.
Mass Preservation	VolumePreservation	1.0, 0–1	Controls cross-section expansion corresponding to primary-axis squash. Silhouette Profile is also passed to secondary-scale calculation.

OverAnim | Safety

UI name	C++ property	Default · unit · range	Effect
Maximum Width Scale	MaxSecondaryScale	2.0, >= 1	Final upper limit for calculated cross-section scale. Runtime adjusts it to at least 1.0.
Maximum Length Scale	MaxPrimaryScale	3.0, >= 1	Final upper limit for Signal Response primary scale. Runtime adjusts it to at least 1.0.

OverAnim (inherited)

UI name	C++ property	Default · unit · range	Effect
Input Composition	CompositionMode	Additive Offset	Additive Offset adds displacement to the previous composed result; Re-Skinning reevaluates from current control-point transforms.

Execution · Signal · Response scope

Item	Behavior
Phase	Shape
Signal	Supported.
Response Mode	Supports Pulse and Sustained. Sustained updates target magnitude and polarity while Signals maintaining the slot arrive.
Automatic Six-Stage Motion	Compatible. The module must be enabled and named. When using a Span, Span Start and Span End must both exist or both be empty. Without a Span, Pivot Bone is required for Pivot Mode Region Bone or Skeleton Bone. Settings dependent on Contact Point, Contact Normal, or Keep Contact Fixed require contact data and cannot be generated by Automatic Six-Stage Motion.

Public Enums

EOverAnimSquashAxisMode

BlueprintType enum used by AxisMode. It selects primary axis only without a Span; with a Span, the endpoint position difference is the axis.

C++ value	Editor UI	Meaning
LocalX	Local X	Uses local X of the selected pivot transform.
LocalY	Local Y	Uses local Y of the selected pivot transform.
LocalZ	Local Z	Uses local Z of the selected pivot transform.
SignalDirection	Signal Direction	Converts finite, nonzero Signal DirectionWS to component space. Rejects requests without a valid direction.
ContactNormal	Contact Normal	Converts finite, nonzero Signal ContactNormalWS to component space. Rejects requests without a valid normal.

EOverAnimSquashPivotMode

BlueprintType enum used by PivotMode, selecting shape pivot transform or location without a Span.

C++ value	Editor UI	Meaning
BoneGroupPivot	Region Bone	Finds PivotBone among current Bone Group control points and uses its transform.
SignalOrigin	Signal Origin	Uses finite Signal OriginWS as a component-space pivot. Rejects without Mesh Component or Origin.
ContactPoint	Contact Point	Uses valid Signal ContactPointWS as component-space pivot. Rejects without contact point.
Auto	Auto	Uses the first valid control-point transform.
SkeletonBone	Skeleton Bone	Resolves PivotBone preferentially from reference control points for a skeleton-based pivot.

EOverAnimSquashAnchorPolicy

BlueprintType enum used by AnchorPolicy, selecting the fixed point for endpoint motion caused by length change.

C++ value	Editor UI	Meaning
PreserveStart	Keep Start Fixed	Fixes Span Start and applies length change toward End.
PreserveEnd	Keep End Fixed	Fixes Span End and applies length change toward Start.
Centered	Split From Center	Splits Start/End movement about the span midpoint.
ContactAnchored	Keep Contact Fixed	Uses a valid Signal contact point as pivot. Rejects without contact point.

EOverAnimSquashAttachmentEndpoint

BlueprintType enum used by FOverAnimSquashAttachmentTarget::Endpoint.

C++ value	Editor UI	Meaning
Start	Start Endpoint	Propagates source Span Start translation delta to the dependent Region.
End	End Endpoint	Propagates source Span End translation delta to the dependent Region.

EOverAnimSquashAttachmentFalloffMode

BlueprintType enum used by FOverAnimSquashAttachmentTarget::FalloffMode.

C++ value	Editor UI	Meaning
Uniform	Uniform	Moves the whole dependent Region at the same weight like one attached mass.
ChainDistance	Chain Distance	Calculates per-bone propagation weights using chain distance from dependent Region root to tip. Enables RootWeight, TipWeight, FalloffExponent.

EOverAnimSquashSpanProfileMode

BlueprintType enum used by SpanProfileMode, selecting axial mapping and secondary silhouette profile between endpoints.

C++ value	Editor UI	Meaning
Uniform	Uniform Scale (Legacy)	Uses linear axial interpolation and constant axial derivative between endpoints.
LinearCenter	Tapered Linear	Uses a profile with linear taper around the center.
SmoothCenter	Smooth Silhouette (Recommended)	Uses a smooth centered profile entering and leaving endpoints without slope jumps.
PowerCenter	Custom Silhouette	Adjusts centered profile exponent with SpanProfileExponent.

EOverAnimSquashSilhouetteBalance

BlueprintType enum used by SilhouetteBalance, selecting emphasis direction for the Span cross-section profile.

C++ value	Editor UI	Meaning
Balanced	Balanced	Uses a silhouette profile symmetric toward Start and End.
StartHeavy	Emphasize Span Start	Moves silhouette emphasis toward Span Start.
EndHeavy	Emphasize Span End	Moves silhouette emphasis toward Span End.

When SpanProfileMode = Uniform, cross-section profile is constant, so the three SilhouetteBalance values produce no visual difference.

Response Rule-only parameters

The Module Response struct for UOverAnimSquashStretchModule is FOverAnimSquashStretchResponseParameters.

UI name	C++ property	Default · unit · range	Visibility · effect
Shape Scale at Full Strength	PrimaryScaleAtMax	0.65, >= 0.05	Primary-axis silhouette scale at response magnitude 1. Below 1 squashes; above 1 stretches. Runtime adjusts to at least 0.05.
Authored Anticipation	AnticipationAmount	0.0, 0–1	Counter-shape amount inside the authored Pulse envelope. It remains in the response struct when Automatic Six-Stage Motion supplies phases separately, but the module uses automatic-phase stage strength.
Authored Anticipation Timing	AnticipationPeakFraction	0.25, 0.05–0.75	Shown when Authored Anticipation > 0. Fraction of Attack Time at which counter-shape peaks.
Authored Recovery Overshoot	bEnableRebound	false	Whether recovery rebound is used inside the authored Pulse envelope.
Authored Overshoot Scale	ReboundPrimaryScaleAtMax	1.08, >= 0.05	Shown with Authored Recovery Overshoot. Primary scale during recovery; runtime safety limit is Maximum Length Scale.
Authored Overshoot Timing	ReboundPeakFraction	0.35, 0.05–0.95	Shown with Authored Recovery Overshoot. Fraction of Release Time at which rebound peaks.

Signal requests require positive finite resolved magnitude, finite nonzero Response polarity, finite Attack/Hold/Release envelope, and the response struct above. Additional input depends on selected settings.

Setting	Required Signal data	Rejection condition
No Span + Axis Mode = Signal Direction	Finite nonzero DirectionWS	Reject without Mesh Component or valid direction.
No Span + Axis Mode = Contact Normal	bHasContactNormal = true, finite nonzero ContactNormalWS	Reject without valid normal.
No Span + Pivot Mode = Signal Origin	Finite OriginWS	Reject without Mesh Component or Origin.
No Span + Pivot Mode = Contact Point	bHasContactPoint = true, finite ContactPointWS	Reject without valid contact point.
Span + Anchor Policy = Keep Contact Fixed	bHasContactPoint = true, finite ContactPointWS	Reject without valid contact point.

Safety · performance · validation

• Runtime must resolve both control points and shape-skeleton bone coverage for a span. Otherwise no proxy is created.
• Attachment Targets create graph edges only for an enabled module with a valid span. No propagation plan is created if source endpoint chain alpha or target Region mask cannot be resolved.
• A Sustained response is released only when slot name and priority match and request priority is not below current priority. Otherwise release is rejected.
• Contact-dependent pivot/axis/anchor accepts requests only with valid Signal input. Prevent Contact Penetration affects shape only when contact data exists.
• Maximum Width Scale and Maximum Length Scale are final safety limits; PrimaryScaleAtMax is first calculated from response magnitude and polarity.