How do I make smaller-resolution renderings appear in the center of the frame buffer?

[Peng_DU]

params.use_resolution_divider = true makes it render smaller-resolution images first.

However, the smaller-resolution images will appear at the bottom of the frame buffer, for example, 8 small ones in a row at the bottom.

It will be better to show 1 small image at the center or make the 1 small image fill the whole frame buffer?

Looks can be done by setting viewport.

Thanks.