Implement current functionality in an ECS.

[kanerogers]

Overview

Great! We picked an ECS, legion. Now comes the fun part - implementing it.

I think the best place to start is Hotham::Program. Ultimately one of the most important things in hotham is making sure that the interface a developer will use to create an app is as simple as possible.

The asteroid could look something like:

struct Asteroid {
  model: Model,
  transform: Transform,
  // new functionality like physics, sound etc. will go here
}

struct Transform {
  position: Vector3<f32>,
  rotation: Quaternion<f32>,
  scale: Vector3<f32>,
}

let mut world = World::new();
let asteroid = Asteroid {
  model: asteroid_model,
  transform: Transform {
    position: vec3(0.0, 1.0, 0.0),
    rotation: Default::default(),
    scale: vec3(1.0, 1.0, 1.0),
  }
}

world.push(asteroid);

That's pretty straightforward. The refinery is the same, except we need to make sure its parent is the asteroid, somehow.

struct Refinery {
  model: Model,
  transform: Transform,
}

struct Transform {
  position: Vector3<f32>,
  rotation: Quaternion<f32>,
  scale: Vector3<f32>,
  parent: Option<Box<Transform>>, // ??
}

This is pretty different from our current Node based structure, which is just lifted from gltf. We'll need to approach the migration of Node to legion based components separately.

What's even trickier is things like Hands, for instance.

struct Hand {
   model: Model,
   transform: Transform,
   animation: Animation,
}

We'd then have something like a HandsSystem that takes the current XR state and updates the Animation and Transform components accordingly.

TODO

• Add legion dependency
• Modify Hotham::Program to return a World
• Break apart Node into Components and Systems #45
• Modify gltf-importer to work with legion #47
• Render Asteroid and Refinery with legion architecture #50
• Implement Hands using legion #51

[kanerogers]

Well, this is fun. legion only lets us have Components as 'static + Sized + Send + Sync. 😄

In essence, we'll have to break Node apart. Right now it's acting as its own ECS, really, and we don't want that.

[kanerogers]

We'll come back to audio later!