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Twitter post by Daniel Feldman (@d_feldman): Linux is the only major operating system to support diagonal mode (credit [Twitter] @xssfox). Image shows an untrawide monitor rotated about 45 degrees, with a horizontal IDE window taking up a bottom triangle. A web browser and settings menu above it are organized creating a window shape almost like a stepped pyramid.
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Ok I was joking with the images but now that I think about it this would likely be pretty useful to have on smart watches with circular displays.
E.g. having the watch face rotating to face towards the wearer would be a pretty neat concept. Definitely something I'd want a toggle for though.