Reflector/Refractor: Add multisampling support.

[Mugen87]

Related issue: #22933

Description

Introducing multisampling support to Reflector and Refractor.

I've noticed there are multiple ways how three.js currently names variables/properties which define how many samples are used in context of multisampling:

• WebGLMultisampleRenderTarget is currently using samples.
• added antialias property to Reflector and Refractor options #22933 suggested the usage of multisample which is used in this PR, too.
• WebGPU and WebGPURenderer use sampleCount.

If I had to make a choice I would pick sampleCount although the others are of course good, too. We should just ensure to use the same syntax everywhere.

[mrdoob]

Thanks!

[mrdoob]

Regarding WebGLMultisampleRenderTarget...

What do you think about removing that class and adding a samples property to WebGLRenderTarget instead?

[Mugen87]

We also have to move ignoreDepthForMultisampleCopy, useRenderToTexture and useRenderbuffer to WebGLRenderTarget then. And closely test with WebXR.

However, after all it's probably best to head for this change since starting with WebGL 2 multisampling is a common thing for all render targets.

[mrdoob]

Exactly. samples should probably be 0 by default though...
Do you want to give it a go?

[Mugen87]

I'll take a look 👍 .

[vanruesc]

It might also be worth considering merging WebGLMultipleRenderTargets into WebGLRenderTarget since multisampling and MRT are currently mutually exclusive as explained in #23300. There's an open PR that appears to address this: #22089.

[mrdoob]

@vanruesc yes, one step at a time though... 🤓