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Behavior Tree Graph Editor - Architecture

Overview​

The BT Graph Editor is integrated into BehaviorTreeDebugWindow with dual debug/editor modes. It renders in a standalone SDL3 window with its own ImGui context.

Hotkey: F8

For complete technical details, see BT_Graph_Editor_Architecture.md in the repository.

Core Components​

1. BehaviorTreeDebugWindow​

Location: Source/AI/BehaviorTreeDebugWindow.h/cpp

Main class with dual functionality:

  • Debug Mode: Runtime visualization, entity list, blackboard, execution log
  • Editor Mode: Full editing with node creation, validation, save/load

Key members:

bool m_editorMode;              // Toggle debug/editor
BTCommandStack m_commandStack;  // Undo/redo management
uint32_t m_selectedNodeId;      // Current selection
bool m_isDraggingPin;           // Connection dragging
BTConfig m_config;              // From BT_config.json

2. BTGraphLayoutEngine​

Location: Source/AI/BTGraphLayoutEngine.h/cpp

Automatic graph layout using Sugiyama algorithm (5 phases):

  1. Layering (BFS)
  2. Initial ordering
  3. Crossing reduction
  4. Buchheim-Walker layout
  5. Force-directed collision resolution

Layout Directions:

  • TopToBottom - Vertical
  • LeftToRight - Horizontal (default)

3. BTEditorCommand / BTCommandStack​

Location: Source/AI/BTEditorCommand.h/cpp

Command pattern for undo/redo (max 100 commands):

  • AddNodeCommand
  • DeleteNodeCommand
  • MoveNodeCommand
  • ConnectNodesCommand
  • DisconnectNodesCommand
  • EditParameterCommand

Keyboard shortcuts: Ctrl+Z (undo), Ctrl+Y (redo)

4. BTConfig​

Configuration from Config/BT_config.json:

  • Layout settings (spacing, grid size, snap)
  • Rendering settings (pin radius, bezier tangent)
  • Node colors by type and status

Node System​

Node Types​

From BTNodeType enum:

Composites:

  • Selector, Sequence, Parallel

Decorators:

  • Inverter, Repeater, UntilSuccess, UntilFailure, Cooldown

Leaves:

  • Action, Condition

Node Statuses​

From BTStatus enum:

  • Running (yellow/orange)
  • Success (green)
  • Failure (red)
  • Invalid (gray)

Editor Features​

Pin-Based Connections​

  • Input pins (left) and output pins (right)
  • Drag from output to input to connect
  • Visual feedback (green = valid, red = invalid)
  • Bezier curves for visual clarity

Validation System​

Real-time validation with BTValidationMessage:

  • Error: Critical issues (red)
  • Warning: Non-critical (yellow)
  • Info: Suggestions (blue)

Rules:

  • Exactly one root node
  • No cycles
  • Decorators: exactly 1 child
  • Composites: at least 1 child

Node Properties Editor​

Edit selected node:

  • Name, action type, condition type
  • Repeat count (Repeater)
  • Cooldown time (Cooldown)

Save/Load System​

JSON V2 Format:

{
  "version": 2,
  "treeId": 123,
  "name": "EnemyAI",
  "rootNodeId": 1,
  "nodes": [
    {
      "id": 1,
      "type": "Sequence",
      "children": [2, 3],
      "editorPosition": {"x": 0, "y": 0}
    }
  ]
}

Templates​

4 built-in templates:

  1. Empty - Single root
  2. Basic AI - Patrol + chase + attack
  3. Patrol - Waypoint patrol
  4. Combat - Combat decision tree

Standalone Window Pattern​

Same pattern as Animation Editor:

Lifecycle:

  1. CreateSeparateWindow() - SDL_Window, SDL_Renderer, ImGuiContext
  2. RenderInSeparateWindow() - Render UI in separate context
  3. DestroySeparateWindow() - Cleanup

Event Handling: ProcessEvent(SDL_Event*) for window close, keyboard shortcuts, mouse events

Integration​

BehaviorTreeAsset​

CRUD operations:

uint32_t AddNode(BTNodeType type, const std::string& name);
bool RemoveNode(uint32_t nodeId);
bool ConnectNodes(uint32_t parentId, uint32_t childId);
bool DisconnectNodes(uint32_t parentId, uint32_t childId);
std::vector<BTValidationMessage> ValidateTreeFull() const;

File Locations​

  • Source/AI/BehaviorTreeDebugWindow.h/cpp - Main editor
  • Source/AI/BTGraphLayoutEngine.h/cpp - Layout engine
  • Source/AI/BTEditorCommand.h/cpp - Command pattern
  • Source/AI/BehaviorTree.h/cpp - Data structures
  • Config/BT_config.json - Configuration
  • Source/OlympeEngine.cpp - Main loop (F8 hotkey)

See Also​

  • Complete architecture document in repo: Docs/Developer/BT_Graph_Editor_Architecture.md
  • Source code: Source/AI/