feat!: Use ServiceLoader for Renderer registry, RendererReadyEntrypoint

[sylv256]

Problem

Because Renderer can be rendered at any point before or during Minecraft's initialization until it is used, problems arise when it's necessary to use it early. For example, in order to disable Indigo, FRAPI implementations need to add a custom field to their fabric.mod.json. Renderers should not need to add a field to their FMJ just to disable Indigo, let alone any other Renderer. Also, mods extending FRAPI such as Conduit need a defined point in time during and after which Renderer is ready to use. All of this introduces inconsistent behavior and quickly becomes a headache. See #3109 for more details.

Solution

This Pull Request overhauls and adds new concepts to FRAPI's Renderer registration.

RendererProvider

interface RendererProvider {
    static RendererProvider get() { // Gets or finds the RendererProvider for the renderer that will be loaded
        // ...
    }

    String id(); // "Renderer ID", usually the mod ID of the renderer

    @ApiStatus.OverrideOnly
    Renderer getRenderer(); // Gets or instantiates the Renderer implementation

    @ApiStatus.OverrideOnly
    default int priority() { // The priority in which this renderer will be loaded (highest loads)
        return 1000; // 1000 is fine for most renderers
    }
}

Instead of manually calling Renderer#register, renderers are now registered with a Service Loader. This lets mods get basic information about the renderer that will be loaded at any point during the game's execution as they can be loaded immediately, and this is especially useful for Mixin Config Plugins.

RendererReadyEntrypoint

In fabric.mod.json, it is defined as fabric-renderer-ready.

Sometimes, mods will want to use Renderer right away, and this is where the issues with the prior system really reveal themselves. Previously, if a mod wanted Renderer, they would have to either use Renderer#get and hope it's already registered, or they would Mixin into Renderer#register to ensure that Renderer has been registered before using it.

Conduit is a library built to create and implement extensions for FRAPI. In order for Conduit's extensions, implementations, and users to use FRAPI and Conduit effectively, a RendererReadyEntrypoint is required. Some operations are best done as soon as the Renderer is ready, so having an entrypoint to ensure code that requires Renderer does not use it before it is registered is powerful.

Tests & Integrity

I've added two checks: one in FRAPI itself to ensure a renderer is loaded, and one in its Client Testmod that asserts RendererReadyEntrypoint is invoked. If either of these conditions fail, an exception is thrown.

Additional Information

Proof that it works

Fixes #3109

[sylv256]

Setting to draft as changes were requested

[PepperCode1]

This javadoc should clarify that this method is called only if this provider is selected and that this method is guaranteed to run at the same time as ClientModInitializer.

[sylv256]

I'm not sure if this is relevant anymore.

[PepperCode1]

If the API exposes the entire RendererProvider instance instead of just the ID, then using an instanceof check like FREX instead of having the ID in the API at all would work. I suggested only exposing the ID because mods should not be creating renderers or checking provider priorities manually.

[sylv256]

Mods may have a genuine need to check the ID of the RendererProvider, so I think we should keep it rather than forcing them to rely on Renderers' implementation details. Everything else can be OverrideOnly.

If it's somehow any better, we can do an instanceof check here since that works in implementation. I just wanted to have a good example of how to use the API.

[sylv256]

???