This document discusses modeling game objects using finite state machines and state diagrams. It provides an example of modeling a monster's states which include idle, moving, attack, hurt, and dead. The modeling process involves two steps: 1) creating an object state diagram to represent the states and transitions, and 2) implementing the model in a game client. Additional sub-states like crawl, walk and run can be added to the moving state. The document also provides an example of implementing a simple desktop calculator using state machines and discusses how to identify the states for the calculator problem.

1. Finite State Machine
Mobile Game Programming
jintaeks@gmail.com
Division of Digital Contents, Dongseo Univ.
October 6, 2016

2. Action states
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 states of the monster
– Idle
– Moving
– Attack
– Hurt
– Dead

3. Simplification
 Step1: How to model the problem to find a solution.
 Step2: How to implement the model.
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4. Step1: Model
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5. Model: Object State Diagram
 The State Diagram is a well known data structure in
computer science.
 In compiler theory, we learn State Diagram which is
used in automata.
 In database, there is an entity-relation model which is
similar to the state diagram.
 In game programming, there is a state machine which
is based on the state diagram.
 We apply this data structure to an object in game.
– It is called ‘Object State Diagram’.
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6. State DiagramState
 A State is represented as a circle.
 Start state has a incoming arrow.
 Final state has a double circle.
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7. State DiagramState Action
 A State can have action(s).
 An action is described in text after slash
symbol.
 An action describes the dynamic
behavior of an object in that state.
 Example:
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State/Action

8. State DiagramTransition
 A transition is represented as a
directed solid arrow.
 A transition means the state change
between two different states.
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 A state transition between A and B.
 It can be read, ‘State A goes to B’.

9. State DiagramTransition Input/Action
 A transition can have input(s) and
action(s).
 An input describes a condition
which trigger the state change.
 An action describes the dynamic
behavior of an object when it goes
to other state.
 Example:
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10. Monster State Diagram
 For simplicity, we only select 3 states.
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11. Final Monster State Diagram
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12. Question
 In Moving state, I want to add more detailed motions
for the monster.
– Crawl
– Walk
– Run
 How to add this feature?
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13. (Answer to Question)
 We can build the ‘Moving State Diagram’.
 Add this sub state diagram into inner state diagram
of Moving State.
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14. Step2: Implementation
 Step1: How to model the problem to find solution.
 Step2: How to implement the model.
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15. Simple Game Client
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17. Adding States
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18. Adding Properties
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m_fIdleTimer
m_dwIdleMotion
m_dwDistanceToTarget
m_fSpellGauge
m_dwAttackMotion
m_dwTargetId
m_dwBboxId
m_fPrepareAttackTimer

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20. Adding State Transitions
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22. State transition: Idle state
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23. State transition: Moving state
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24. State transition: Attack state
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25. Test routine
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27. Demo
 The Simple Console application project using
Microsoft Visual Studio 2010.
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User press a ‘1' key.
User press a 'Esc' key.
 Question: There is an output sequence of 1 and 0
after first 1 is printed. Why?

28. (Answer to question)
 In Moving state, the condition of first if-statement is
always true. Because the string expression “target is
out in range” always returns a non-zero value.
 In C++, a non-zero value evaluated to true for a
boolean expression.
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29. (Implementation Optimization)
 Our C++ implementation can be structured to more
elegant form.
 We can use well-known design patterns.
 Use the pointer to member functions!
– I will show it in the next lecture.
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30. More Complex Example
 Most programmer are aware of this concept.
 But they cannot use it freely, why?
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31. Implementing Simple Desktop Calculator.
◇Input ◇Output
• 1
• +
• 2
• +
• 13
• =
• +
• 3
• -
• …
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1
2
1
16
3
3
16
13
1
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32. How to Find States? Let’s focus on number.
1 + 2 + 13 = + 3 -
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first operand
second operandsecond operand

33. Can you find a hidden state?
1 + 2 + 13 = + 3 -
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The result can be used as first
operand, but also it can be
discarded.

34. 3 States for Calculator problem
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35. Homework: Complete the Calculator State Model.
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36. Q&A
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