WebGLRenderer: Remove program reference from materials.

[Mugen87]

This PR ensures that Material.program is not set by the renderer anymore. If the renderer needs access to the current material's program, the following approach should be used:

const materialProperties = properties.get( material );
const program = materialProperties.program;

The refactoring makes the code more clear since the instance of WebGLProgram is now retrieved in a single way. Besides, it does not leak in materials and thus is no part of the public API anymore. It's also necessary to remove Material.program for solving #15047 anyway.

The only place that was necessary to change was WebGLRenderLists.

[mrdoob]

Sweet! This definitely needs to happen.

Not sure properties.get( material ) will solve the actual problem though.

We may need something like:

programs.get( mesh );

If a material is reused by a Mesh and a InstancedMesh, two different programs would be produced, so we need to be able to get the program from a higher level.

Happy to merge this but I don't see how the new API could transition to a more suitable one without breaking again.

[Mugen87]

Not sure properties.get( material ) will solve the actual problem though.

Yes, that's true. I'm currently trying a few things out to solve #15047 and I thought this small refactoring is something we can do now. The usage of Material.program just feels irritating since at first glance you wonder why a reference to WebGLProgram is stored at two places. Besides, the material is public and I don't think users should have access to a program property.

programs.get( mesh );

The signature probably needs scene and renderer as additional arguments too since the program also depends on scene and renderer parameters. Since solving #15047 will be a big change for WebGLRenderer, I would prefer to implement it gradually. Meaning preparing the code base for the "big" PR (in the hope that it will be fairly small 😇 ).

[mrdoob]

The usage of Material.program just feels irritating since at first glance you wonder why a reference to WebGLProgram is stored at two places. Besides, the material is public and I don't think users should have access to a program property.

Definitely, it was a mistake to make it public.

Since solving #15047 will be a big change for WebGLRenderer, I would prefer to implement it gradually. Meaning preparing the code base for the "big" PR (in the hope that it will be fairly small 😇 ).

Yeah... Okay, if anything, this change will let us see how many people rely on material.program.

[mrdoob]

Thanks!