Enabling render region and setting render border

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1

I want to enable the render region function and set the render border values from within cycles source code - is that possible?
From what I have found those values come from properties in the blender scene that gets synced, but I have found no way to modify them.
(I’m currently only interested in the rendered mode for the viewport, if that makes a difference)

Thanks

2

The Camera class has border_* members that define the render border.

3

I know about that one, but how do I tell cycles to use render borders? There seems to be a use_borders() in the properties that get passed from blender, but I can’t find out where/if cycles saves it.