I've seen several implementations that have input components to mark entities that should react to input

Useful for webgl-based UIs and other interactable stuff

We need to clear the PixiCache.ts cache when an entity is removed from the Engine

It should be adjacent to one side and movable via a key press/mouse
This issue can be done in the same PR as #4

It is useful for the entities to hold a reference to the engine. Not having an engine set is also useful as it allows the creation of prefabs.

As a player I want to shoot bullets in 4 directions. Bullets should have spread.

The ParticleContainer class is a really fast version of the Container built solely for speed, so use when you need a lot of sprites or particles.

http://pixijs.download/release/docs/PIXI.particles.ParticleContainer.html

Basically, it does exactly what it says; it smooths the deltaTime:

Say the frame rate is humming along at 30 fps, then you experience a hiccup of a few frames at 15. DeltaTime will report a difference of 2 ms (30 fps = 2ms / frame, 15 fps = 4ms / frame), but smoothDeltaTime will report something closer to 2ms (but weighted by the frame loss).

https://forum.unity.com/threads/time-smoothdeltatime.10253/

Note: this should not be part of the core ECS, buit an supeset on top of PIXI's update loop

When possible, diry components should update existing instances.
When components are removed internal engine objects should be cleaned.

Players should have health and a health bar
Healthbars should change color as value decreases
Healthbars should follow players (see #20)

We should test the ECS to guarantee performance.

We should clear previous engine instances when hot reloading

Health bars need to follow entities as well!

We need a way to simply define and consume entity pools

Engine: expose an specialized camera entity
Gameplay: camera should follow player

What happens when a component requires the existence of another one? By definition components should be independent.

Use-cases:
Shapes should reuse transform's position/scale
Camera should reuse transform's position

We need a solution that includes:

• Stats.js (https://github.com/mrdoob/stats.js) for fps/memory monitoring
• A telemetry solution for quick reporting and comparison of time series data