What I learned building an enemy state machine in Godot 4

Building an enemy state machine in Godot 4 taught the author several valuable lessons. Initially, using a match statement seemed sufficient for simple enemies, but problems arose when more states were needed. The author discovered that match statements become unwieldy once there are four or more states, with bugs emerging from complex transition grids rather than within individual states.

The first lesson learned is that a match statement is adequate for early-stage implementation but becomes problematic when more than three states are required. When a fourth state is introduced, the match block starts to resemble a grid of every state combination, leading to bugs that are hard to track down.

Lesson two emphasizes that bugs in state machines typically lie in transition logic rather than within individual states. Many issues stem from one state leaving behind critical data or flags that the subsequent state fails to check or reset correctly. For instance, an enemy might get stuck in an attack animation because the hurt state didn't clean up the attack timer properly.

The third lesson focuses on the benefits of using a Node-per-state approach, particularly when dealing with multiple enemy types that share some behaviors but have distinct others. Instead of using a single Node for all states, creating separate Nodes for each state allows for easier swapping of state logic without affecting unrelated states. This approach becomes especially useful when multiple enemy types are present, each with their unique set of states and behaviors.

Lastly, the author stresses the importance of treating the "dead" state as a regular state in the state machine. Historically, bugs arose when health checks were scattered throughout the codebase rather than being handled consistently within the state machine. By assigning "dead" its own state with proper enter and exit functions, such issues can be avoided. This ensures that once an enemy reaches the "dead" state, it cannot transition back to any other state, eliminating confusion and potential life-saving bugs.

In summary, starting with a match statement for simple state machines is acceptable, but as complexity grows, adopting a Node-per-state structure becomes essential. Additionally, explicitly defining states like "dead" and handling transitions cleanly are crucial steps to building robust and maintainable state machines.