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Flow Nodes

Flow nodes contain at least one child node, and control the execution of a behavior tree by describing the rules by which each of their children nodes must be executed. The different types of Flow nodes are as follows.

Sequence

Description

Executes each of its children nodes in the order that they're defined, one at a time, until one child fails or all children nodes succeed.

Parameters Accepted

None.

Results

Outcome

Criteria

Success

When all its children nodes returns a successful result.

Failure

When a child node fails.

Additional Information

  • Must have at least one child node specified.
  • Maximum number of children nodes: 255.

Selector

Description

Executes each of its children nodes in the order that they're defined, one at a time, until a child node succeeds.

Parameters Accepted

None.

Results

Outcome

Criteria

Success

As soon as one of it children nodes returns a successful result.

Failure

If all of its children nodes return a failure.

Additional Information

Must have at least one child node specified.

Priority 

Description

Executes each of its children nodes in decreasing order of their priority, one at a time; each child node is assigned a priority level (the top-most/first child being of the highest priority) and a condition that is evaluated dynamically.

This means that a child node is executed only if its associated condition is satisfied; as soon as a node fails its condition check, the conditions of lower priority children nodes are re-evaluated.

Execution then resumes at the node with the highest priority and a satisfied condition.

Parameters Accepted

Parameter Name

Description

Value

Condition

Specifies the condition that needs to be satisfied for a child node to be executed.

Boolean; an empty field will always be evaluated as true.

Results

Outcome

Criteria

Success

If the child node that is currently being processed returns a successful result.

Failure

If the current child node returns a failure.

Additional Information

The last child node of a Priority node must be defined with an empty condition, that always yields a successful result.

This node acts as a "fallback", representing the default behavior that must be carried out if all higher priority children of the Priority node have failed.

Parallel

Description

Executes its children nodes in parallel.

Parameters Accepted

Parameter Name

Description

Value

Success/ Failure Mode

Specifies how the Parallel node's children influence its result of success and failure as stated below.

  • All
  • Any



Results

Outcome

Criteria

Success

  • If all children nodes return a successful result when the Success Mode parameter has been set to All.
  • If at least one of its child nodes returns success when the Success Mode parameter has been set to Any.

Failure

  • If all children nodes return success when the Failure Mode has been set to All.
  • If at least one of its child nodes returns failure when the Failure Mode has been set to Any.

Additional Information

Maximum number of parallel children nodes: 32.

Loop

Description

Has only a single child node, which it executes either a fixed number of times, infinitely or until the child fails.

Parameters Accepted

Parameter Name

Description

Value

Repeat Count

Specifies the number of times the node must loop the execution of its child node.

Integer. Loops infinitely when set to 0.

Results

Outcome

Criteria

Success

If the loop of execution runs for the specified Repeat Count.

Failure

If the Loop node's child fails.

Additional Information

None.

Loop Until Success

Description

Has only a single child node which it executes either a fixed number of times, infinitely or until the child succeeds.

Parameters Accepted

Parameter Name

Description

Value

Repeat Count

Specifies the number of times the node must loop the execution of its child node.

Integer. Loops infinitely when set to 0.

Results

Outcome

Criteria

Success

If the node's child returns a successful result.

Failure

If the node's child fails even after the loop of execution runs for the specified Repeat Count.

Additional Information

None.

State Machine

Description

Has one or more States as its children that are executed in the order they are defined, one at a time. At any time, the state of a State Machine node is the same as the state of its child that is currently being executed.

Every State must have as part of its definition:

  • Transitions, that specify the events under which the State transitions to another State.
  • A root node that begins a separate behavior tree that must be executed when the current State is active.


Parameters Accepted

States

Parameter Name

Description

Value

State Name

Allows users to specify a custom name for the created State.

Must be a unique string value for the current State Machine node.


Transitions

Parameter Name

Description

Value

Trigger Event

Specifies the Event upon which the current State transitions to a Destination State.

Accepts any Built-in or Game event from a dropdown menu.

Destination State

Defines the State Name the current State must transition to upon the occurrence of the above Trigger Event.

Accepts any created State as its value.

If the Destination State is the current State itself, the current State will first be terminated and re-initialized before being updated again.

Results

Outcome

Criteria

Success

If the State child node that is currently being processed succeeds.

Failure

If the current State child node fails.

Additional Information

None.

Send Transition Event

Description

Allows Events to be sent from within a defined State of the parent State Machine node, hence triggering a transition to the Destination State of the State Machine.

Send Transition Event nodes are used in conjunction with State Machine nodes, to trigger transitions from one State of the State Machine node to another.

Parameters accepted

Parameter Name

Description

Value

Event

Specifies the Event that needs to be sent by the defined State of the State Machine node.

Accepts any Built-in or Game Event as its value.

However the Event must be previously specified in the Trigger Event field of the parent State machine node.

Results

Outcome

Criteria

Success

If the defined transition Event was sent successfully.

Failure

If the transition Event wasn't sent successfully.

Additional Information

None.

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