Add Selector node to BT

Source/Engine/AI/BehaviorTreeNodes.cpp

@@ -99,6 +99,40 @@ BehaviorUpdateResult BehaviorTreeSequenceNode::Update(BehaviorUpdateContext cont
     return result;
 }
 
+int32 BehaviorTreeSelectorNode::GetStateSize() const
+{
+    return sizeof(State);
+}
+
+void BehaviorTreeSelectorNode::InitState(Behavior* behavior, void* memory)
+{
+    auto state = GetState<State>(memory);
+    new(state)State();
+}
+
+BehaviorUpdateResult BehaviorTreeSelectorNode::Update(BehaviorUpdateContext context)
+{
+    auto state = GetState<State>(context.Memory);
+
+    if (state->CurrentChildIndex >= Children.Count())
+        return BehaviorUpdateResult::Failed;
+
+    auto result = Children[state->CurrentChildIndex]->InvokeUpdate(context);
+
+    switch (result)
+    {
+    case BehaviorUpdateResult::Success:
+        return BehaviorUpdateResult::Success;
+    case BehaviorUpdateResult::Failed:
+        state->CurrentChildIndex++; // Move to the next node
+        if (state->CurrentChildIndex < Children.Count())
+            result = BehaviorUpdateResult::Running; // Keep on running to the next child on the next update
+        break;
+    }
+
+    return result;
+}
+
 int32 BehaviorTreeDelayNode::GetStateSize() const
 {
     return sizeof(State);

Source/Engine/AI/BehaviorTreeNodes.h

@@ -45,6 +45,26 @@ private:
     };
 };
 
+/// <summary>
+/// Selector node updates all its children (from left to right) until one of them succeeds. If all children fail, the selector fails.
+/// </summary>
+API_CLASS() class FLAXENGINE_API BehaviorTreeSelectorNode : public BehaviorTreeCompoundNode
+{
+    DECLARE_SCRIPTING_TYPE_WITH_CONSTRUCTOR_IMPL(BehaviorTreeSelectorNode, BehaviorTreeCompoundNode);
+
+public:
+    // [BehaviorTreeNode]
+    int32 GetStateSize() const override;
+    void InitState(Behavior* behavior, void* memory) override;
+    BehaviorUpdateResult Update(BehaviorUpdateContext context) override;
+
+private:
+    struct State
+    {
+        int32 CurrentChildIndex = 0;
+    };
+};
+
 /// <summary>
 /// Root node of the behavior tree. Contains logic properties and definitions for the runtime.
 /// </summary>