Horizontal or vertical split preview feature for adjustments
I know I'm probably asking for a pony here, but filing this just in case: it would be awesome if there was a way for the adjustments popover dialog's live effects to be comparable to the photo's original color parametric effects. Ideally with the choice between not just vertical splitting, but also horizontal splitting. This could be governed by a set of 3 linked buttons, something like:
Preview:
[ Full | ½ horizontal | ½ vertical ]
GIMP has this "Split view" feature for most (if not all) its filters, but I'd see this being even more useful in Shotwell given that multiple non-destructive effects are applied at once.