Support Custom Renderers about three-elements

[RangerMauve]

Would it make sense to enable this by defining new custom elements? Like <three-svg-game>?

[CodyJasonBennett]

I think so, but I like your suggestion of having modified elements for <three-game> rather than child elements that merely modify its behavior. I suppose this would depend on how we deal with custom cameras, etc.

[hmans]

I'm tinkering with a few ideas for this. The one that feels best so far revolves around providing the various bits and pieces that are currently hardcoded into the monolithic <three-game> element as separate elements that can be combined as the user needs them, with <three-game> being reduced to just a "starter configuration" of these.

For example, we'd have <three-ticker>, <three-webgl-renderer>, <three-css-renderer>, etc., and you'd either use them directly (if you need the configurability), or through a <three-game>, <three-css-game> etc. template.

One of the downsides of this idea is the potential for namespace collisions. If we introduce a <three-ticker> element, and a future version of Three.js itself exposes a THREE.Ticker, we'll have a collision that needs to be resolved somehow.

At the same time, we've been discussing (on Discord) to establish a separate "extras" package that, similar to react-drei for react-three-fiber, provides elements that implement specific functionality (using code from Three.js' examples), like GLTF loading, Orbit Controls and so on. It's possible that there is a synergy between this and the things discussed above.

[hmans]

I'm tackling this now. The goal is to allow the user to create instances of these renderers by using their corresponsing <three-*> tags, eg. <three-css-3d-renderer>, and having them automatically hook up with the <three-game> element. (There is probably no need to use the newly introduced DOM CSS selector referencing here, since there will always only ever be a single renderer -- and projects where even this does not apply for some wild reason will most likely not be static HTML projects.)

[hmans]

PR for the first pass on this: #43

[hmans]

I've merged #43, which allows customization of renderers that live in the THREE.* namespace. I'm deferring support for CSS/SVG renderers to 0.4.

[hmans]

In the interest of pushing out a 0.4 release soon, I'm moving this to the next milestone.