Control Flow Nodes Overview

Control flow nodes direct the execution path of a behavior tree. They manage how child nodes are scheduled, evaluated, and short-circuited based on child tick results (Success, Failure, or Running).

Forester supports three fundamental control flow nodes:

1. Sequence Nodes (sequence)

• Behavior: Evaluates children sequentially from left to right.
• Short-circuiting:
  • Returns Failure immediately if any child returns Failure.
  • Returns Running if a child returns Running (halting further evaluation during that tick).
  • Returns Success only when all children return Success.
• Use Case: Step-by-step procedures (e.g. [Check Precondition -> Execute Step 1 -> Execute Step 2]).

Detailed documentation: Sequence Nodes.

2. Fallback / Selector Nodes (fallback)

• Behavior: Evaluates children sequentially from left to right to find a successful path.
• Short-circuiting:
  • Returns Success immediately if any child returns Success.
  • Returns Running if a child returns Running.
  • Returns Failure only when all children return Failure.
• Use Case: Error handling, recovery strategies, and fallback routines (e.g. [Primary Action -> Secondary Fallback Action -> Alert Operator]).

Detailed documentation: Fallback Nodes.

3. Parallel Nodes (parallel)

• Behavior: Ticks children concurrently during each engine tick.
• Completion Policy: Evaluates overall status based on child results and configured threshold policies (e.g., success threshold or fail-fast rules).
• Use Case: Concurrent tasks (e.g. [Maintain Balance while Navigating to Goal]).

Detailed documentation: Parallel Nodes.

Summary of Return States