Expose MeshPortalMaterial RenderTarget

[frankievx]

Describe the feature you'd like:

I'm working with the MeshPortalMaterial and I'm interested in running a custom shader effect that is dependent on an initial snapshot of the scene in order to define a color palette. In order to accomplish this, I need access to the internal portal's render target in order to read the pixels. I think the benefit of exposing the render target allows for more control and the ability to apply postprocessing effects to the portal.

Suggested implementation:

I'd be happy to implement this however would want some feedback on if this is a good idea or not before i spend the time and effort.

[github-actions]

Thank you for contributing! We’re marking this issue as stale as a gentle reminder to revisit it and give it the attention it needs to move forward.

Any activity, like adding an update or comment, will automatically remove the stale label so it stays on our radar.

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[github-actions]

We’re closing this issue to keep our project manageable and make room for other active work, but we truly appreciate your effort and contribution.

If you’d like to continue working on this, please feel free to re-open it or reach out on Discord — our community is always ready to support you. Thanks again for helping us stay organized and for understanding our approach!