Roadmap

Planned for 0.1.0

• Simplify component creation using one of the strategies detailed below (see below)

• Tiled platformer example! Probably will port over Blorp, probably with shinier new sprites from a free asset pack.

Beyond that, probably

• More collisions stuff

• First-class events

• DOM rendering thing/React integration?

Preloader/Preloader Hooks

It'd be fun and cute to ship a default preloader, but most games will probably not have enough assets to ever see it anyways, so might be more important to document how you could make your own, and actually provide the hooks needed.

Collision System

Now that Pearl has a more fleshed-out set of Colliders and a KinematicBody, more stuff can be added to the collision system.

Some things I'd like:

• how do non-KinematicBody things collide

  • is it time for RigidBody to happen

    • physics are hard and scary :(

• collisionEnter/collisionContinue/collisionExit events

  • on collide: set colliding to true and collisionEnter fired (along with collisionContinue?)

  • continue firing collisionContinue every frame

  • on exit: collisionExit event

    • how is exit triggered??

    • this is actually really tricky w/ current KinematicBody implementation :I

  • if entity destroyed, fire collisionExit

  • unity handles this by literally just not supporting these events for two kinematic bodies colliding

    • instead: https://docs.unity3d.com/ScriptReference/CharacterController.OnControllerColliderHit.html

    • also see: https://docs.unity3d.com/Manual/class-Rigidbody2D.html

    • I think Godot maybe also does this? hmmm

Other questions

• Could entities be grouped into a single top-level "scene" component?

  • Scene component would get all children and create collision pair tests between them

• Is it fine for collisions to exist as just another system in a component's update hook, or should it have special component hooks and exist in a special system?

  • Unity does the latter - why?

    • Superpowers does not, fwiw, and there may be others that don't.

  • Collisions generally need to be resolved before updates happen (see Coquette)

    • Pre-update hook?

• Long-term considerations

  • Collision layers? Would help avoid triggering/calculating unnecessary collisions

Networking Thoughts

There's ~zero chance networked multiplayer will ever be a core component in Pearl, but it's good to keep in mind, especially as Sledgehammer is theoretically ongoing.

For example: Physical.vel is being removed in favor of manually moving entities and, eventually, maybe using physics, or at least some sort of MovingBody that you can apply a velocity to. However, Physical.vel had the nice property of allowing (sorta) "predictive" movement, rather than purely relying on the incoming position. Adding a real physics engine might help with this, but that's obviously fraught with its own peril, as Manygolf showed.

Any automated collision system should keep this in mind, too. It'd be annoying to have collisions duplicated on server and client, requiring a if (!isHost) {return} check, but it might make sense.

Simpler Entity Creation

Entity creation is currently a kind of awkward process, depending on what you want to do. Specifically:

• The settings passed through to create() and init() create an awkward second set of preconfigured properties

• Overriding settings created by e.g. a factory or "prefab"-like construct requires the original component to have special logic:

type Settings = {sprite?: Sprite};

class MyComponent<Settings> {
  sprite?: Sprite;

  init(settings: Settings) {
    // check to see if this has already had a sprite set on it
    if (settings.sprite && !this.sprite) {
      this.sprite = settings.sprite;
    }
  }
}

• On the other hand, strategies like the above could leave a component in an invalid state - e.g. what if MyComponent can't function without a set sprite?

• It's also hard to subclass components when base class needs settings - have to copy logic to apply settings, or create helper method.

Magic Components

TypeScript (as of 2.1) now makes it easy to create a type-safe API similar to the original Coquette entity construction API:

export class MagicSettingsComponent<T> extends Component<any> {
  constructor(settings: Partial<T> = {}) {
    super();
    for (let key of Object.keys(settings)) {
      this[key] = settings[key];
    }
  }
}

interface ISpriteRendererProperties {
  spritePath: string;
  scaleX: string;
}

class SpriteRenderer extends MagicSettingsComponent<ISpriteRendererProperties>
  implements ISpriteRenderer {
  spritePath?: string;

  create() {
    console.log(this.spritePath);
  }

  renderSprite() {
    // ...
  }
}

new SpriteRenderer({ spritePath: 'foo.png' });

This would make reasoning about setting and using properties before and during initialization much easier.

There are some potential downsides:

a) Settings that are only used during initialization, and then discarded, would still have to defined as properties on the component.

b) TypeScript's keyof includes methods/getters/setters, requiring an interface to be defined without these. This is annoying bit of boilerplate :(

c) The component wouldn't have type-safe required settings:

class MyComponent extends Component {
  a: string;

  create() {
    console.log(this.a.toUpperCase());
  }
}

// errors out because a is not passed
this.pearl.entities.add(new Entity({
  components: [new MyComponent()],
});

However, this may not be a big deal, as "required" settings are in opposition to being able to update settings after construction anyways. Maybe some kind of helper could be added to throw out automagically if required settings are missing at create() (or init()) time?

d) Setters that depend on the parent object may error out with this.

An experimental implementation of this exists at the ideas/magic-components branch.

Alternatives To Magic Components

• Add merge-properties helper, which additionally ensures that properties passed in settings don't override properties that have been set

• Validate required properties at construction time, with type guarantees - non-optional settings

  • What if the user really wants to defer setting properties on the object for some reason?

    • User should just suck it up and e.g. pass partially-filled out setting through control flow

Devtools Inspector

This is its infancy at Pearl Inspect.

The goal of the Pearl Inspector will be to add a simple display of entities in the world (shown in the parent-child hierarchy) and their components. For more information on the roadmap and status of this project, see its TODO file.

Canvas scaling utilities

It'd be great to offer canvas scaling utilities, like scaling-on-resize while maintaining the original aspect ratio (using ctx.scale, that is, not CSS that causes blurry images). It'd also be cool to have a full-screen toggle.

Design Questions, etc.

This is an unsorted list of things I've been thinking about.

• How are objects created/destroyed?

  • Figure out better API for entities.add/entities.destroy

  • Maybe this.createObject({...}) / this.destroyObject({...})

• Add better utilities for managing destroyed objects and components

  • Unity's able to automatically null references to destroyed objects. I don't think there's any magic I can do for that in TS/JS, unfortunately.

  • Make destroyedObject.getComponent() give an explicit error

• How are "game controller" level components handled?

  • Singleton example in Unity: https://unity3d.com/learn/tutorials/projects/2d-roguelike-tutorial/writing-game-manager

  • Useful SA discussion on Unity singletons starts here: http://forums.somethingawful.com/showthread.php?threadid=2692947&userid=0&perpage=40&pagenumber=444#post462272736

• Figure out additional hooks for components

  • For example, collision needs to be broken up into "detection" and "resolution" phases, so that e.g. an enemy that turns around when it hits a block can be coded as two separate components

  • FixedUpdate-like hook? Does this even make sense in a single-threaded application? Seems suuuper difficult to time and schedule correctly.