Render resolution mask / blur mask

[knowledgenude]

First consider that I don't know nothing about rendering, and i don't have any idea about the right work on this.

By render resolution mask, i mean the possibility to mask the resolution from lower to higher in the same frame.

The black area is the lowest res and white area is the default res, the possibility to add a gradient between the two colors would be nice. I never see this in a game, if someone know some game that use it, let me know.

The reason i am requesting this is about performance but can be used for other cool stuffs too. I think that set a area of the screen for low ress mean more performance, so this can affect the other post processing stuffs too, like ssao, rtao, bloom, etc. maybe bloom can be even "disabled" for blurred areas. The only example i see a stuff like that, is in cycles. If am not sleeping, there are a way to render just a specific part of the render to have more speed.

For example, we can put a "vignette" mask faking the real eye focus, where just the middle of the eye is cappable to see fine detail.

In shooters, the player aim is always in the center, there is a tendency of the player in almost all kind of games to focus the center of the screen, so we can discart the unnecessary res or give more "realism" in horror or survival games / interactive scenes where the user have to move his "virtual eyeball" to see the fine details like is in real life. If there are not a performance addition in this, i think that just a blur mask would be very useful, even for blurring a simple object in scene, for call menus, blur nudity, etc.