Tasks Reference

Tasks are the building blocks of a State Tree. Each state executes one or more tasks while it is active. Vertex Animation Studio ships the following tasks through the VA StateTree Schema:

Play Vertex Animation - plays a single animation
Play Random Vertex Animation From Pool - picks one animation from a pool each time the state is entered
Randomize Bool - rolls a 50/50 boolean into a referenced property
Set Int Parameter / Set Float Parameter / Set Bool Parameter / Set String Parameter / Set Gameplay Tag Parameter - writes a value into a referenced property

To add any of these, select a state in the StateTree editor and click + in the Tasks panel.

Play Vertex Animation

The workhorse task: plays a single named animation on the instance for the lifetime of the state.

Property	Type	Default	Description
Animation	VA Compatible Animation	-	The animation to play. Dropdown is filtered by the collection set in the tree’s Asset Details.
Play Rate	Float	`1.0`	Playback speed multiplier.
Random Start Position	Bool	`false`	Picks a random start position per instance so crowds don’t animate in lock-step.
Start Position	Float	`0.0`	Normalised start time (0–1). Hidden when Random Start Position is enabled.
Blend Duration	Float	`0.2`	Blend time (seconds) when transitioning into this animation from whatever was playing.
Loop	Bool	`false`	If `true`, the animation loops indefinitely and the state never completes on its own. If `false`, the state fires `On State Completed` when the clip ends. Pair with an `On State Completed` transition.
Reverse	Bool	`false`	Plays the animation backwards.

Tip: For looping behaviours you usually want Loop on. For chained or event-driven behaviours (idle → wave → idle) you usually want Loop off so the state can complete and transition. Blend Duration is what makes transitions between states feel smooth rather than snapping.

Play Random Vertex Animation From Pool

Picks a random animation from an array each time the state is entered. This is the State Tree equivalent of the Animation List Random mode, but driven by state-machine logic.

Property	Type	Default	Description
Animation Pool	Array of VA Compatible Animation	-	The candidate animations. One is picked uniformly at random on state entry.
Play Rate	Float	`1.0`	Playback speed multiplier.
Random Start Position	Bool	`false`	Picks a random start position per instance.
Start Position	Float	`0.0`	Normalised start time (0–1). Hidden when Random Start Position is enabled.
Blend Duration	Float	`0.2`	Blend time (seconds) into the picked animation.
Loop	Bool	`false`	Loop the picked animation.
Reverse	Bool	`false`	Play the picked animation in reverse.

Put idle_1, idle_2, idle_3 in the pool and every crowd member rolls their own. Great for breaking up visual repetition across large crowds.

Randomize Bool

Rolls a 50/50 boolean and writes it into a referenced bool property. Use it on state entry to seed branching decisions for conditions on outgoing transitions.

Property	Type	Description
Set Property	Bool property reference	The tree parameter (or bound property) that will receive the rolled value.

Note: The roll is a fair 50/50 (FMath::RandBool()). If you need weighted probabilities, use Set Float Parameter with a random range and compare the output in a transition condition.

Example: In an Idle state, Randomize Bool → WillCheer. Add a transition: On State Completed, Condition: WillCheer == true, Next = Cheer. Half of all idle loops chain into a cheer.

Set Parameter

There are five Set Parameter tasks, one per supported value type. Each writes a value into a referenced property on state entry.

Task	Value Type	Supports Random Range
Set Int Parameter	Int32	✅
Set Float Parameter	Float	✅
Set Bool Parameter	Bool	-
Set String Parameter	FString	-
Set Gameplay Tag Parameter	FGameplayTag	-

Set Int Parameter / Set Float Parameter

Both numeric variants share the same properties, differing only in the numeric type.

Property	Type	Default	Description
Set Property	Int32 / Float property reference	-	The target parameter to write.
Use Random Range	Bool	`false`	If `true`, the value is rolled in a random range on every state entry. If `false`, a fixed Value is written.
Range	Int32 Interval / Float Interval	`0–1` / `0.0–1.0`	Min/Max inclusive range. Hidden when Use Random Range is off.
Value	Int32 / Float	`0` / `0.0`	Fixed value to write. Hidden when Use Random Range is on.

Example: weighted choice: Set Float Parameter → DecisionValue, Use Random Range enabled, Range 0.0 – 1.0. Then on outgoing transitions, use conditions like DecisionValue < 0.7 → Idle and DecisionValue >= 0.7 → Cheer for a 70/30 split.

Set Bool Parameter

Property	Type	Default	Description
Set Property	Bool property reference	-	The target parameter.
Value	Bool	`false`	The fixed value to write.

Set String Parameter

Property	Type	Default	Description
Set Property	String property reference	-	The target parameter.
Value	FString	`""`	The fixed value to write.

Set Gameplay Tag Parameter

Property	Type	Default	Description
Set Property	GameplayTag property reference	-	The target parameter.
Value	FGameplayTag	(empty)	The fixed tag to write.

Example: mood tagging: On entry to each reaction state, Set Gameplay Tag Parameter → CurrentMood = Mood.Excited. A later state can branch on CurrentMood via a tag-matching condition without needing the original event tag.

Combining Tasks

A state can hold multiple tasks. They enter in the order they are listed on the state. Parameter-setting tasks (Randomize Bool, Set ... Parameter) don’t tick; they write their value on entry and immediately report success. The next task in the list then enters. A common pattern:

Randomize Bool or Set Parameter: seeds parameters on state entry.

Play Vertex Animation (Loop off): plays the animation for the state’s lifetime.

Outgoing transitions read the seeded parameters via conditions when the animation completes.