Improve render asset

[vallrand]

Objective

• Remove duplicated implementation of asset extraction/preparation in material/material2d
• Allow to have multiple GPU representations for the same "main world" asset.

Solution

Remove one to one correlation between "main world" asset and GPU asset, by swapping base type that implements RenderAsset to be the GPU asset type. That would make RenderAssetPlugin more flexible, being able to prepare different data based on same source asset (example: effect plugin could preprocess mesh buffer data for specialized rendering, without affecting main render flow).
That also makes RenderAssets<GPUType> more explicit.

Changelog

Changed

• RenderAsset trait definition
• Material and Material2d now use RenderAssetPlugin
• RenderMaterials and RenderMaterials2d were replaced with more generic RenderAssets

Migration Guide

• RenderMaterials<M> can now be accesed as RenderAssets<PreparedMaterial<M>>
• RenderMaterials2d<M> can now be accesed as RenderAssets<PreparedMaterial2d<M>>
• RenderAssets<Image> is now RenderAssets<GpuImage>
• RenderAssets<Mesh> is now RenderAssets<GpuMesh>
• RenderAsset trait should now be implemented on prev RenderAsset::PreparedAsset type, while source asset type is defined as RenderAsset::SourceAsset

Before

impl RenderAsset for Image {
    type ExtractedAsset = Image;
    type PreparedAsset = GpuImage;

    fn extract_asset(&self) -> Self::ExtractedAsset {
        self.clone()
    }
}

After

impl RenderAsset for GpuImage {
    type SourceAsset = Image;
    type ExtractedAsset = Image;

    fn extract_asset(source_asset: &Self::SourceAsset) -> Self::ExtractedAsset {
        source_asset.clone()
    }
}

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[JMS55]

Do you have a specific use case in mind for "Allow to have multiple GPU representations for the same "main world" asset"?.

I'm exploring ideas for reducing copies of render assets in memory by deleting them from RAM once they're on the GPU's VRAM.

[vallrand]

@JMS55

That multiple representations was perhpaps a bit misleading.
From the perspective of decoupling generic "main world" types
from specific rendering implementation, as example if one would want to swap to renderer implementation where mesh assets are all kept in one large buffer, but keep using Handle<Mesh>.

One could always just duplicate the original asset, if it needs to be uploaded to the gpu twice.

Wrote some feedback if you'll find it useful 8132

[JMS55]

After some further experimentation with meshlets and ray tracing, I'm in favor of something like this PR.

[superdump]

@vallrand - could you update this PR? I have long disliked the split between RenderAssets and RenderMaterials and wanted materials to be just another asset.

[superdump]

I've adopted this in #12827 as it was a great idea, ahead of its time. :)