Camera editor up grade (composition guides)

[Mostache]

Hi,
It would be nice to have default composition guides on the viewport camera options.
An example of composition guides in Blender with multiple options.

Also it would be nice to have a darker color in the viewport out of the frame to really focus on the shot composition.

Example:

[Calinou]

• Related to Make it so a viewport can have ' darkened ' boxes to be 16:9 format . . #2136.

There was a PR implementing darkened boxes, but it was closed due to that proposal not being well-received. It's probably better to open a new proposal that is more well thought-out and describes the options that would be exposed. However, we should avoid adding too many editor settings here as this is a relatively advanced option and it's easy to get caught up.

[Mostache]

I'm skeptical about this being an advance feature. I find it to be a basic and mandatory for composition.
Its understandable that it should be well though out but really, just a check box in the viewport drop down menu under cinematic preview.
Darker areas are less important to honest.