FMontageSubStepper

struct Engine Since unknown

#include "Animation/AnimMontage.h"

Description

Internal helper struct, declared alongside UAnimMontage, that steps montage playback time forward or backward one section/branching-point/time-stretch-marker at a time per call to Advance().

Caveats & Gotchas

• Private engine implementation detail owned by FAnimMontageInstance — there is no Blueprint or public gameplay API surface for it.
• It exists specifically because a single frame's DeltaTime can span multiple sections, loop points, or TimeStretchCurve markers; Advance() is called repeatedly within one montage tick to sub-step through each of them.
• Plain C++ struct (not a USTRUCT), so none of its fields are reflected, replicated, or visible to Blueprint.

Functions (11)

Sub-Stepping 11

Sub-Stepping

11 ▼

Access	Type	Name	Description
public	function	FMontageSubStepper::AddEvaluationTime	Queues additional delta time onto the sub-stepper's TimeRemaining for Advance() to consume in subsequent sub-steps.
public	function	FMontageSubStepper::Advance	Moves montage playback position forward or backward by up to one sub-step, stopping at section boundaries, branching points, or TimeStretchCurve markers, and reports what happened via EMontageSubStepResult.
public	function	FMontageSubStepper::ClearCachedData	Invalidates the cached combined play rate so it is recomputed the next time ConditionallyUpdateCachedData runs.
public	function	FMontageSubStepper::GetbPlayingForward	Returns whether the sub-stepper is currently advancing the montage position forward rather than backward.
public	function	FMontageSubStepper::GetCurrentSectionIndex	Returns the index into the montage's CompositeSections array for the section the sub-stepper currently occupies.
public	function	FMontageSubStepper::GetDeltaMove	Returns the montage-position delta produced by the most recent Advance() call.
public	function	FMontageSubStepper::GetRemainingPlayTimeToSectionEnd	Computes how much playback time remains between the given original-space position and the end of the current section, accounting for any TimeStretchCurve on the montage.
public	function	FMontageSubStepper::GetRemainingTime	Returns the delta time still queued for the sub-stepper to consume across subsequent Advance() calls.
public	function	FMontageSubStepper::HasReachedEndOfSection	Returns whether the most recent Advance() call landed exactly on the current section's boundary.
public	function	FMontageSubStepper::HasTimeRemaining	Returns whether the sub-stepper still has unconsumed evaluation time to work through via further Advance() calls.
public	function	FMontageSubStepper::Initialize	Binds the sub-stepper to a montage instance, caching its Montage pointer, resetting per-frame state, and re-evaluating the TimeStretchCurve if one is present.

Properties

Access	Type	Name	Description
private	property	FMontageSubStepper::Cached_CombinedPlayRate	Cached combined play rate (montage rate scale times global rate scale) used to derive PlayRate and DeltaMove without recomputing it every sub-step.
private	property	FMontageSubStepper::Cached_P_Original	Records the "original" authored-space position that Cached_P_Target was last derived from, used to detect when the target-space cache needs recomputing.
private	property	FMontageSubStepper::Cached_P_Target	Cached montage position in time-stretched "target" space, lazily recomputed from Cached_P_Original whenever the source position changes.
private	property	FMontageSubStepper::CurrentSectionIndex	Index into the montage's CompositeSections array for the section the sub-stepper is currently positioned in.
private	property	FMontageSubStepper::CurrentSectionLength	Duration, in the montage's original timeline, of the section CurrentSectionIndex refers to.
private	property	FMontageSubStepper::CurrentSectionStartTime	Start time, in the montage's original timeline, of the section CurrentSectionIndex refers to.
private	property	FMontageSubStepper::DeltaMove	The signed distance the montage position moves during the current sub-step, exposed read-only via GetDeltaMove().
private	property	FMontageSubStepper::Montage	Cached pointer to the UAnimMontage asset being sub-stepped, mirrored from the owning FAnimMontageInstance's Montage field.
private	property	FMontageSubStepper::MontageInstance	The owning montage instance this sub-stepper is advancing time for, set by Initialize().
private	property	FMontageSubStepper::PlayRate	Effective play rate used for the current sub-step, derived from Cached_CombinedPlayRate and, if present, the TimeStretchCurve's local rate at the current position.
private	property	FMontageSubStepper::TimeRemaining	How much evaluation time is still left to sub-step through this tick; drained by successive Advance() calls and refilled by AddEvaluationTime().
private	property	FMontageSubStepper::TimeStretchMarkerIndex	Index into the montage's TimeStretchCurve marker list tracking which time-stretch segment the sub-stepper currently occupies.
private	property	FMontageSubStepper::bHasValidTimeStretchCurveData	True when the montage has a usable TimeStretchCurve and its marker data was successfully built during Initialize(), enabling per-position play rate adjustment.
private	property	FMontageSubStepper::bPlayingForward	True while the sub-stepper is moving montage time forward; false when the effective play rate is negative and it is stepping backward.
private	property	FMontageSubStepper::bReachedEndOfSection	Set by Advance() when the sub-step landed exactly on the current section's boundary, signalling the caller should evaluate a section change, loop, or blend-out.

Version History

Introduced in: unknown

Version	Status	Notes
5.6	stable	—

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