Nodes: Add Post-Process MaskPassNode

[cmhhelgeson]

Related issue: #28962

Description

Add a strictly post-processing masking implementation to Nodes. The example contains the ability to switch between two post-processing outputs, one with regular masks and one with inverse masks.

Issues:

1. Cannot switch back to regular post processing after switching to inverse mask post processing.
2. Need to able to call .applyMask() on a base scene pass itself rather than applying it as a texture argument to the function.
3. Determine whether other mask effects need to be implemented within this class.

Live Example

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
684 kB (169.4 kB)	684 kB (169.4 kB)	+0 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
460.9 kB (111.2 kB)	460.9 kB (111.2 kB)	+0 B

[sunag]

I'm finding the amount of code for this example a bit unjustified. Could you remove the inverse mask for now, and instead of having a new MaskPassNode just add something like?

const maskPass = ( scene, camera ) => pass( scene, camera ).setMRT( mrt( { output: output.a } ) );

// ...
const sceneMask1 = maskPass( scene1, camera );
const sceneMask2 = maskPass( scene2, camera );

[Mugen87]

Definitely! I would also favor a solution without the need for a separate module like MaskPassNode.

TBH, I was never a fan of the previous API MaskPass and ClearMaskPass and how it was integrated into the composer.