Problem with exact rendering

Hey guys. I am a 2d(venturing into 3d) artist I use nomad on Android and choosing the part of the scene to render always leads to either chopped off details or wasted resolution, so I kinda came up with something that seems like a solution.
A rectangular selection box will be very useful. see the pictures attached.(I mean "RECTANGLE in the second image @stephomi I wish this would come with the next update🙂

Typing in the exact resolution wanted would also be very useful @stephomi