Gsplat API improvement suggestion

[mvaligursky]

The main goal is to expose the ShaderMaterial that is used to render splats, and allow users to create and assign a custom material.

At the moment the material creation is internal, and without a public API to access it. To provide custom shader, this needs to take place:

entity.gsplat.materialOptions = {
            fragment: '// shader source',
            vertex: ''// shader source'
};

Suggested new API:

class GSplatInstance - make it a public class
GSplatInstance.material - make its material property public,
                // allowing new materials to be assign and their properties modified

GsplatComponent.instance   // make the getter public, returns GSplatInstance, allowing access to the material

example of custom shader, with custom material properties:

    const material = new ShaderMaterial({
        uniqueName: 'MySplatMaterial',
        vertexCode: ` // custom code or shaderChunks.gsplatVS`,
        fragmentCode: '// custom code or shaderChunks.gsplatVS',
        attributes: {
            vertex_position: SEMANTIC_POSITION,
            vertex_id_attrib: SEMANTIC_ATTR13
        }
    });

    // default settings (we could apply those internally, but perhaps better to leave control with the user)
    material.cull = CULLFACE_NONE;
    material.blendType = BLEND_PREMULTIPLIED;

    // customisations
    material.setDefine('MYDEFINE', 'VALUE');
    material.setParameter('myparam', 3);

    // assign material
    entity.gsplat.instance.material = material;

Thoughts @slimbuck @willeastcott ?

[slimbuck]

I like this, but how will the data-specific material properties be applied to the material?

There are data-specific defines (SH_BANDS, GSPLAT_SOGS_DATA, etc), textures (means_l, means_u, ... etc) etc.

[slimbuck]

The gsplat material also requires a specific set of base attributes as you mention above.

It's kind of strange to require a user to know all of this. It's almost like you'd want the engine to create a default config that the user can then customise.

[mvaligursky]

User will only create and set what he needs. The rest can be handled internally.

In the simplest case, they do not provide material and we create one. This matches to how RenderComponent can be created without material - we use a default standard material.

They can also create Material and specify custom vertex / fragment shaders.

Under the good, when engine receives the material, it will set up all defines and textures as needed.

So the material will pretty much only allow shader customisation, but they can also set up defines their shaders need.

[mvaligursky]

closing, addressed in #7749