I've decided to evolve a game design, called Slinger and use this blog as an experimental repository for the ideas, as did Danc in his excelent Lost Garden. The design for slinger will be posted as a series and downloadable prototypes will be accessible from here as well.
The series will consist of incremental and iteractive essays about the game:
1 - Introduction and basic game mecanics (april 01, 2008)
2 - Reward system and difficulty management (april 02, 2008)
3 - Setting ideas (april, 03, 2008)
4..N - Iteractive reviews of the design (during april 2008)
N+1 - Post Morten (when finished...)
Introduction
Slinger will be an action game where the player takes the role of a boy equiped with a sling. Armed with the sling and rocks, he has to defend his farm's animals againts all sorts of threats.
Player mecanics
Slinger is a 3rd person view 3D game where the player uses the keys to move the character and the mouse to turn it. Moving around the area there will be animals, that tend to run away from him, and other scene elements, like fences, barns, trees, etc.
To throw rocks the player uses the mouse. By holding the left-button, the sling stay in armed position. The player stretches the sling's rubber by pulling back the mouse. The rock is thrown when the players releases the button. While the sling is hold armed, the player is free to move with the keys and "aim" by moving the mouse from side to side, remembering that the sling's power is controlled by the disntance he moves the mouse back.
Animals behavior
Animals in Slinger will behave as in nature, moving as groups, and being predators and preys. The preys will try to avoid the predators and the player, while predators will try to attack the preys (when hungry) and avoid the player (except when they decide that he's also a prey).
Final thoughts
I've decided to start with the basic mechanics because it's the first thing I must implement and test. If the basic mechanics is not fun, nothing else will be. In the next post I'll write about some reward system ideas to make the game enjoyable in the long run (not so long, since the game is intended for casual players).
Fell free to comment on the idea...
Mar 31, 2008
Mar 29, 2008
Dependency Injection in Games
Games and OOP
Only a few domains map to a programming paradigm so directly as computer games and object orientation. A Game class matches the concept of a virtual world where several different instances of a GameObject class reside. The simulation usually consists of a loop inside the Game class with three main goals: collect and interpret user or network input; update each GameObject instance based on input and/or a simulation step; draw visible game objects on the output device.
Inheritance vs. Composition in game objects (Deja-vu):
To represent different types of simulated objects, the programmer usually create subclasses of GameObject. There are problems with the inheritance approach since objects from different hierarquies sometimes have common functionality and characteristics. This is a common issue in object oriented software design and replacing inheritance by composition is strongly recomended [check previous posts]. The GameObject class then consists only of an unique identifier, some common attributes all game objects have such as position and orientation and, most important, a collection of components. Each class implementing the GameComponent interface represents a different aspect/behavior of a GameObject such as visuals, physics, AI or health, depending on game being implemented. These components are highly flexible and easier to maintain while also maximize code reuse with many of them being useful in several different game genres.
What is the problem with inter-dependent components?
Composition also has its drawbacks, mostly when there's some coupling between components. For example, an AI component commonly depends on the existance of a health component to decide actions to take and also on a physics component to apply movements to. These dependencies are normally solved directly by the programmer, as shown in the following Java code, part of an AIComponent class, adapted from C++ example Cris Stoy put in his excelent article in Game Programmin Gems 6:
1 public void update() {
2 GameObject owner = getOwner();
3 HealthComponent health = owner.getComponent(HealthComponent.class);
4 if (health != null) {
5 // take appropriate actions
6 }
7 }
Aparently there's nothing wrong with this code, but a closer inspection shows that:
a) lines 2-4 have nothing to do with the expected game logic of an AI update, being just boilerplate code;
b) if no instance of HealthComponent is initialized for this particular GameObject, no proper AI action (line 5) will ever be taken, making it hard to debug.
How to circunvent that?
What I think is a good idea is the use of dependency injection [check Martin Fowler's article] to automatically take care of the coupling between game components and safe initialization. The programmer will not need to manually check for dependencies or their nullability. It is easier to concentrate on the game logic to implement by replacing the above code with this:
1 @Inject(nullable=false)
2 private HealthComponent health;
3 public void update() {
4 // take appropriate actions
5 }
The above code is smaller, considerably cleaner and also safer since our framework will stop initialization and show an error log if there is no HealthComponent initialized for the GameObject that owns this AI component. With this approach we believe one can write better code and achieve faster prototyping which is always desired in game production pipelines.
In the next post more details about how GCore uses dependency injection to safely initialize game objects and its components...
Only a few domains map to a programming paradigm so directly as computer games and object orientation. A Game class matches the concept of a virtual world where several different instances of a GameObject class reside. The simulation usually consists of a loop inside the Game class with three main goals: collect and interpret user or network input; update each GameObject instance based on input and/or a simulation step; draw visible game objects on the output device.
Inheritance vs. Composition in game objects (Deja-vu):
To represent different types of simulated objects, the programmer usually create subclasses of GameObject. There are problems with the inheritance approach since objects from different hierarquies sometimes have common functionality and characteristics. This is a common issue in object oriented software design and replacing inheritance by composition is strongly recomended [check previous posts]. The GameObject class then consists only of an unique identifier, some common attributes all game objects have such as position and orientation and, most important, a collection of components. Each class implementing the GameComponent interface represents a different aspect/behavior of a GameObject such as visuals, physics, AI or health, depending on game being implemented. These components are highly flexible and easier to maintain while also maximize code reuse with many of them being useful in several different game genres.
What is the problem with inter-dependent components?
Composition also has its drawbacks, mostly when there's some coupling between components. For example, an AI component commonly depends on the existance of a health component to decide actions to take and also on a physics component to apply movements to. These dependencies are normally solved directly by the programmer, as shown in the following Java code, part of an AIComponent class, adapted from C++ example Cris Stoy put in his excelent article in Game Programmin Gems 6:
1 public void update() {
2 GameObject owner = getOwner();
3 HealthComponent health = owner.getComponent(HealthComponent.class);
4 if (health != null) {
5 // take appropriate actions
6 }
7 }
Aparently there's nothing wrong with this code, but a closer inspection shows that:
a) lines 2-4 have nothing to do with the expected game logic of an AI update, being just boilerplate code;
b) if no instance of HealthComponent is initialized for this particular GameObject, no proper AI action (line 5) will ever be taken, making it hard to debug.
How to circunvent that?
What I think is a good idea is the use of dependency injection [check Martin Fowler's article] to automatically take care of the coupling between game components and safe initialization. The programmer will not need to manually check for dependencies or their nullability. It is easier to concentrate on the game logic to implement by replacing the above code with this:
1 @Inject(nullable=false)
2 private HealthComponent health;
3 public void update() {
4 // take appropriate actions
5 }
The above code is smaller, considerably cleaner and also safer since our framework will stop initialization and show an error log if there is no HealthComponent initialized for the GameObject that owns this AI component. With this approach we believe one can write better code and achieve faster prototyping which is always desired in game production pipelines.
In the next post more details about how GCore uses dependency injection to safely initialize game objects and its components...
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