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Components

Introduction

Entity Component System (ECS) is a software pattern used in game development. The idea is that in-game objects (called entities) can be customized by adding or removing objects (called components) during runtime. Components add functionalities or behaviors to the entities to which they are attached to. In SurgeScript, both entities and components are objects - the difference is conceptual.

As an example, consider an in-game object called Parrot. Objects by themselves are empty; they do nothing. However, an interesting behavior of parrots is that they are blabbers: they keep repeating the same thing over and over again. So, let's create an empty object called Parrot, tag it as an entity and spawn the Blabber component on it:

object "Parrot" is "entity"
{
    blabber = spawn("Blabber");

    state "main"
    {
    }
}

object "Blabber"
{
    state "main"
    {
        if(timeout(2)) // blab every 2 seconds
            state = "blab";
    }

    state "blab"
    {
        Console.print("Hello!");
        state = "main";
    }
}

Now, whenever you spawn a Parrot, it will keep blabbing (parroting) unceasingly:

Hello!
Hello!
Hello!
...

Suppose now that your Parrot is a Kamikaze Robot: it blabs so much that it will explode itself after some time. We'll attach a Time Bomb to the parroting robot, so that it will stop blabbing after a while:

object "Time Bomb"
{
    state "main"
    {
        if(timeout(15)) // explode after 15 seconds
            state = "explode";
    }

    state "explode"
    {
        Console.print("BOOOM!");
        parent.destroy(); // destroy the parent object
    }
}

object "Parrot" is "entity"
{
    blabber = spawn("Blabber");
    bomb = spawn("Time Bomb");

    state "main"
    {
    }
}

Now, here's the result:

Hello!
Hello!
Hello!
Hello!
Hello!
Hello!
Hello!
BOOOM!

In this example, Parrot is an entity and Blabber and Time Bomb are its components. Once the entity is destroyed, its components (its children) are also destroyed automatically.

Design considerations

In some implementations of ECS, entities are implemented as integers and components consist of raw data only. The game logic is executed by the System layer, which iterates throughout all entities continuously and executes the logic according to the components attached to them.

In SurgeScript, components execute their own code and can be attached to entities simply by spawning them as children. Still, you can use the former approach if you wish to do so.

Composition over inheritance

SurgeScript does not explicitly support inheritance, a feature found in other object-oriented languages. The usage of components is encouraged instead. SurgeScript favors composition over inheritance, allowing for greater flexibility when defining in-game objects.