Allow previewing 2D/control nodes in 3D camera preview

[ecameracci]

Describe the project you are working on

A 3D platformer project that has UI.

Describe the problem or limitation you are having in your project

I would like to have control nodes displayed as part of the camera preview.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Quickly iterating on UI design would be a lot faster if the camera preview allowed for previewing control nodes in the scene.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

This could be done by selecting the camera in the scene tree and selecting the camera preview checkbox, then also having the option to also preview the UI, perhaps with an additional checkbox which displays the canvas layer in the camera viewport.

Quick mock-up of the idea:

If this enhancement will not be used often, can it be worked around with a few lines of script?

I think this could be done with a viewport node, but isn't as clean of a solution as it would be required for every scene with a camera.

Is there a reason why this should be core and not an add-on in the asset library?

This seems like a feature that should be standard and everyone would use when designing 3D games.

[Calinou]

This is currently what happens on the master branch (the current 3D viewport is kept as the 2D editor background), but I don't know if it's a bug or intended behavior. It's been like this ever since the Vulkan renderer was merged.

Edit: The above no longer occurs as of 4.0.stable.

[elvisish]

This would also be great if it were possible to preview canvas nodes such as fullscreen shader effects on top of the preview window for 3D, not just for camera preview but the general 3D scene view.