the option to flip the webcam stream vertically has no effect. for my camera orientation to work, it needs to be rotated 90 (works) and flipped vertically (doesn't work).
Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ... as much data as possible)
stock standard octoprint distribution fresh installation on a pi3. everything else works perfectly. using the raspberry pi camera.
ideally I'd like to rotate 270 instead ... is that even possible? due to the hardware mount and the way the cable is routed, it is not possible to flip the camera.
But you can do both horizontal and vertical flip at the same time, which gets you a true 180 degree rotation (twice mirrored = not mirrored). Add 90 degree to that, and you have 270 degrees (or -90 if you wish).
Edit: to put it more mathematically: the three boolean options give you 2 to the power of 3 options: 4 normal views (0, 90, 180 and 270) and the same 4 views in a mirrored version.
Of course any even counts of flips cancel out the mirror effect. You could even get a 270 degree rotate with 2*n flips if the axes don't have to be at 0 or 90 degree, e.g. if there were the option to flip at 45 degree
Edit: I hadn't thought of combining all 3 options to get a 270 degree rotate. Maybe because rotate and flip aren't commutative and the order isn't specified, but in this special case the order isn't relevant because the rotation rotates one flip axis onto the other.