Lecture 4 - Systems | Games Engineering

# Lecture 4 - System Dynamics
### SET09121 - Games Engineering

<br /><br />
Kevin Chalmers and Sam Serrels

School of Computing. Edinburgh Napier University

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# Recommended Reading

Game Design Workshop. 3rd Edition. Fullerton (2014).
- Read Chapter 5 on System Dynamics.

![image](assets/images/gdw_book.jpg)

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# Example -- Donkey Kong: what do you see?

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# What is a System?

- An example of a system is an engine.
 - This is why we are building an engine in the module.  
- An engine is a system with a particular objective.  
 - That objective is to power some form of manual action.  
- We can apply our formal elements into thinking about systems.

![image](assets/images/engine.jpg)

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# What is a System? Defining Objects

**Objects**

- Objects are the basic elements of a system. Consider the objects you define in object-oriented development.
 - A system is the interaction between a collection of objects.  
- For example: an engine, steering wheel, and wheels interact together to allow a car to operate.  
- The complexity of the underlying system is hidden behind an interface. For a car, this is the steering wheels and pedals.  
- Objects are defined by their properties and behaviors. 
- What objects can you see in other systems?

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# What is a System? Object Properties

**Properties**

- Properties are the attributes of the objects in a system.  
- From an OO point of view, properties are values stored in the object, which may themselves be objects.  
- Properties are the descriptive data that can be analysed, extracted or modified.  
- Properties are also a method to allow unique identification of individual objects.  
- What are the properties of objects you see in other systems?  
- From our rules (Formal Elements) we have extracted most of our objects and their properties.  
- Rules (Formal Elements) --> Objects and their Properties.

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# What is a System? Object Behaviours

**Behaviours**

- Behaviours are the actions that an object undertakes.  
 - Object-orientation calls these methods.  
 - Some of the behaviours are on the state of the object.  
  - An engine requires fuel to be turned on.  
  - We will look at state and state management later in the module.  
  - Remember: our formal rules can restrict our formal procedures.  
 - Behaviours can be complicated.  
- What object behaviours of objects do you see in other systems?  
- Rules and Procedures of Formal Elements can help us extract some of the object behaviours.  
 - Rules and Procedures -> Behaviours (Systems)

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# What is a System? Relationships Between Objects

**Relationships**

- Once we have a collection of objects we can define some rudimentary systems.
- Objects themselves do not form a system. Systems are relationship between the objects.  
 - Depend on the context of use.
     - A car engine turns wheels.
     - A jet engine propels a plane.
 - We must determine the relationships between our objects to create a system.
- A game is a system!  
 - With a shiny graphical front end.
 - Remember: the graphical presentation is almost separate from the system operation.

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# Objects in games

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# Games as Systems: Objects

**Objects**

- Objects are the basic elements of a system.
 - In games the most basic of object is usually called an **Entity**.
 - Almost everything in a game is an object.  
     - For example: players, opponents, environment.  
 - As developers we must identify these objects and develop them.  
 - Games are similar to standard applications although the object relationship are probably more dynamic.  
- What objects can you identify in the games you play?

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# What Objects Are Here?

![image](assets/images/mario.jpg)

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# Games as Systems: Properties

**Properties**

- Define the data attached to an object.
- Some common properties include:
    - Position.  
    - Graphic.  
    - A flag (bool) to indicate whether the object is alive.  
- A basic entity in a game can have numerous properties and sub-components.  
 - RPG in particular has lots of properties.
 - We will examine how we compose objects later.
- What properties can you identify in the games you play?

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# What Properties are Here?

![image](assets/images/dragon_age.jpg)

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# Behaviours

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# Games as Systems: Behaviours

**Behaviours**
- Define what our objects can do.
- We are normally thinking about what can happen during the update step.  
 - For example, when B is pressed the player should jump.  
 - Player's actions are normally based on the controls (Procedures from Formal Elements).  
 - Computer controlled actions are normally supplied via some form of Artificial Intelligence.  
- The physical objects are normally controlled by the physics system.  
- What behaviours do you see in the games that you play?

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# What Behaviours are Here?

![image](assets/images/minecraft.jpg)

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# What Behaviours are Here?

![image](assets/images/pacman.gif)

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**Describe your favourite game as a system.**

Pick one of your favourite games and described the objects, their properties and their behaviours.

Keep it abstract, but consider how you would program these.

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# Relationships

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# Games as Systems: Relationships

**Relationships**

- Games have complex and dynamic relationships based on the game state.
- Some relationships are simple.  
    - The game character relates to the world via a position.
- Some relationships can be based on the current state.  
    - If character is evil then guards will chase on sight.
- Relationships can also be defined by the rules of the game.  
- Possibly the hardest concept to understand in software development.  
- May also cause difficulties later in development when considering optimisation.

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# What Relationships are Here?

![image](assets/images/cities_skylines.jpg)

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# De-constructing Games

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# De-constructing Tic-Tac-Toe
- A system is more than the objects that make it up.  
 - Dynamic relationships cause unforeseen interactions and Conflict.  
 - Small changes in object properties can have a dramatic effect.  
- Tic-Tac-Toe (noughts and crosses) is a simple game.  
 - **Objects:** squares. 
 - **Properties:** symbol within the square (`O`, `X`, or empty).
 - **Behaviours:** set symbol in square.
 - **Relationships:** based on location of matching symbols. Important considering the gameplay mechanic.

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# Tic-Tac-Toe Game States

![image](assets/images/tic-tac-toe.jpg)

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# De-constructing Chess
- Chess is a significantly more complex and strategic game than Tic-Tac-Toe.
- From a system's point of view, chess and tic-tac-toe are very similar.
 - **Objects**: squares, pieces.
 - **Properties**: colour, rank, location of piece.
 - **Behaviours**: move piece.
 - **Relationships**: location of piece to other pieces.
- Why is the outcome so different?

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# Game Flow

- The key difference is the range of possibilities.
- Games should offer possibility; unpredictability. 
- A game also needs to be simple.  
- Games can be defined by the flow of possibilities or structure through the game.  
- As stated: objects are simple; the relationships between the objects lead to the complexity.

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# Game Flow

![image](assets/images/gameflow.png)

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# Example Systems

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# Economics
- Many games have a simple economy where resources can be exchanged.
 - Remember that Resources are a Formal Element.
- The use of currency is seen in a wide range of games:  
 - RPGs.
 - Assassin's Creed series.
 - Batman: Arkham series.
 - etc.
- What does an economy require from a systems point of view?

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# What systems does an Economy need?

![image](assets/images/economics.png)

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# Emergent Systems

- Emergent systems exhibit behavior not explicitly programmed. The behavior emerges from the rules placed on the objects.
 - Birds flocking is such a behavior.
 - Very relative to game AI.
- Nature is full of such systems.
- Examples include: Game of Life; Spore; The Sims (sort of).

![image](https://66.media.tumblr.com/303da0502e45b38484e73b174b3db9db/tumblr_nhte1rMwH01teec4eo2_500.gif)  
 ![image](https://media.indiedb.com/images/articles/1/182/181609/flock4.gif)

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# Software System
- The common approach to writing software is object-orientation.
 - Standard model in C#, Java, and used in C++.
- With object-orientation we have:
 -  **Objects**: which are instances of classes.
 -  **Attributes**: which are the properties of the objects.
 -  **Methods**: which are behaviours associated with objects.

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# Software System

![image](assets/images/uml.png)

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# Back to Donkey Kong

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# System Interaction and Control
- A system does not always need interaction.
 - A game definitely does.  
- Some things to consider:  
 - What information is provided to the player about the system?  
 - What can the player control?  
 - How does the player control these objects?  
 - What feedback occurs within the system?  
 - How do these considerations affect the gameplay?  
- A game will require tuning and polish to get all of these correct.

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# Summary

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# Summary
- From this lecture you should understand:
 - **Objects:** the parts that make up a system.
 - **Properties:** the values that define the objects of the system.
 - **Behaviours:** what functions does an object perform in a system.
 - **Relationships:** how do the objects interact with each other.
- You should use these principles to try and de-construct games thatyou are familiar with.

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# Summary

- **Objects** 
- **Properties**
- **Behaviours**
- **Relationships**

** This is how Object Orientation Works **

OO is a great way of describing and building systems of objects (games)

However; in practice, actually programming these systems can be tricky. There are other extensions to OO that we will cover later. But designing an planning the OO way is a great way to design systems that will exist as software.