Render Region following cursor

[Tamyl]

Hi,
Sometimes I have some noise on a specific, small region of my render, so I would like to focus rays on my cursor position.
I think that there's no path tracing renderer with such option, and I think it would be so useful!
Take a look:

[romullus]

Duplicate: https://forum.corona-renderer.com/index.php/topic,678.0.html