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My friend running Ubuntu just called me saying: "my screen got flipped, how to fix it?"

I told him how to fix it but that raises the question, why is it possible to flip the screen? On Linux you could flip the screen, on windows you could make it rotate sideways.

I can't think of any reason that would make the feature useful, if you want to rotate a picture you could do that in the image viewer.

What type of users flip their Linux or Windows screens? For whom is this feature created?

closed as primarily opinion-based by harrymc, Run5k, Ramhound, Braiam, Journeyman Geek Dec 11 '18 at 14:54

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    It's necessary for users ɐıʃɐɹʇsn∀ uı – bmargulies Dec 9 '18 at 19:17
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    I was reading color inversion until I arrived at the words rotate sideways. – Chris Dec 9 '18 at 22:08
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    A much harder question: Why is this part of the OS, and not part of the display? I'd guess this goes back to VGA or earlier. – Peter Dec 9 '18 at 22:30
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    @Peter - because not all displays have this feature, and having this feature in both your monitor and your OS doesn't hurt anything, whereas having this feature in neither is inconvenient if you need it. – TLW Dec 10 '18 at 1:41
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    With "flip" I read "mirror" (over a horizontal or vertical axis), which I find harder to justify. But the actual question: Given that rotate +90 and -90 (=+270)degrees is the normal thing (for landscape/portrait orientation), it would be extra work to block 180degrees as an option! Ceiling-mounting a monitor to display a menu in a snackbar would be a useful application, but not frequent enough to bother programming for --- but rotating screens has been normal from the very first TFT/flatscreens (not CRT). – user3445853 Dec 10 '18 at 13:45
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One common case where you'd want to turn your screen upside down is if you have a laptop doubling as a tablet computer, like this:

Leonovo Yoga in tablet mode

Another common case is if you attach a projector to the ceiling instead of letting it stand on a table, or using a rotated (and thus portrait) monitor.

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    You can also bounce a projector off a mirror, which requires the projector or OS to support displaying a mirror image. I've done this for back-projection in tight spaces. – Chris H Dec 9 '18 at 20:13
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    To be fair this has been a feature of e.g. nVidia drivers since long before anybody used a desktop OS on/as a tablet. – Lightness Races with Monica Dec 9 '18 at 20:53
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    @LightnessRacesinOrbit It's not just the NVIDIA drivers, it's been around in some form or other in many drivers for multiple decades, mostly because of projectors. – Austin Hemmelgarn Dec 10 '18 at 1:43
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    @AustinHemmelgarn Yes, it was just an example ("e.g." means "for example"). I was thinking of the old little proprietary control panel you'd get that you could use to flip the screen around aaaages ago, but yes my whole point is that this is not in any way a new technology. The whole tablet thing is very new by comparison. – Lightness Races with Monica Dec 10 '18 at 1:44
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    Some Standard VESA mounts allow rotation, which won't signal to the PC hardware that the orientation has changed. Since the prevalence of 'Widescreen' formats, some people like to rotate a screen 90 Degrees to allow working on long documents easier. – Stese Dec 10 '18 at 9:35
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Addressing the sideways rotation part of the question, the main time I've done so is when I've wanted to see many lines of content at once, e.g. a long file of code, a terminal output, or a spreadsheet. Some desktop monitors (e.g. this one) have a stand that rotates by 90°, but the software needs to rotate the video output too, otherwise everything becomes harder to read.

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    +1 for addressing sideways rotation; back before 27" monitors were the norm my favored workspace setup was two 23" monitors, one rotated sideways and off to the side for viewing documentation while the standard orientation was my main screen for doing work. – fluffy Dec 9 '18 at 19:39
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    Wow that's so smart – Lynob Dec 9 '18 at 20:41
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    @Lynob This concept has actually been around for almost half a century. The original Xerox Alto systems (the first computers with a graphical interface) used a screen in a portrait orientation like this because they were designed specifically for document processing. The use of a landscape orientation came about largely for viewing videos, and has largely stuck around because displaying a 16:9 video on a 9:16 screen wastes a huge amount of space. – Austin Hemmelgarn Dec 10 '18 at 1:51
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    @AustinHemmelgarn What type of video viewing was this? I would have guessed that video viewing on computer monitors was not very common before the 90's, and the landscape orientation norm must be considerably older than that. – jkej Dec 10 '18 at 9:46
  • @jkej I'm talking about more modern cases with 16:9 displays. For the old 4:3 stuff, portrait versus landscape just doesn't matter enough for people to care one way or another, so the use of TV CRT's in computer monitors largely dictated the aspect ratio and orientation at the time. Once 16:9 started becoming an option, landscape versus portrait started mattering again, but landscape remained the predominant option because of video viewing, not because it was inherently better in some other way. – Austin Hemmelgarn Dec 10 '18 at 14:26
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One can envision a circumstance in which the display mounting and associated brackets can only permit an inverted attachment of the panel. A kiosk with limited access may be one example, a display unit mounted at ceiling height with a mounting bracket that cannot be attached unless upside down.

In the case of a laptop, I can picture a situation in which the keyboard is mounted inside a box with the display extending outside the enclosure which would require to invert the image for viewing in a normal orientation.

I expect there are other circumstances in which this applies.

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    I've seen plenty of ceiling-mounted monitors where they used this exact feature as described, so it's not as hypothetical as this answer may read. – Mast Dec 10 '18 at 8:59
  • Beakers are often mounted upside down, however they usually feature a facility to flip the input signal themselves – eckes Dec 10 '18 at 11:07
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    @eckes If you mount a beaker upside down, wouldn't whatever liquid you put in it just fall out? – Glen Yates Dec 10 '18 at 18:10
  • Beamer of course ;) – eckes Dec 10 '18 at 19:30
  • @eckes the strange thing is that hardly anyone outside Germany uses "Beamer" to mean projector - but Beamer comes from English – Chris H Dec 11 '18 at 11:09
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Many restaurants show their menus on rotated screen (portrait mode); same for airports Departure and Arrival lists. Newer ones are simple oversize screens with 90 degree rotated display.

Others have already mentioned reasons for mirroring (projecting via a mirror to fold the distance needed; or back-projecting), and for 180 degree rotations (set-up tablets, etc.)

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    The 180degree is just an artefact from allowing the +90 and -90 degree, no thought went into it. "Wait we can flip it upside down now? Any reason to forbid it? No? Fine"... The applications you describe are consequences of this possibility, not desired applications that demanded the possibility. – user3445853 Dec 10 '18 at 13:52
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    @user3445853 Do you have any evidence of that claim? I could just as reasonably imagine situations where "we have to install this upside down" is a real practical concern. I don't see why you assume it wasn't also added as a legitimate feature that could have practical purposes. – JMac Dec 10 '18 at 18:38
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In the past monitors could be rotated on their mounts 90 degrees each way. Haven't seen that for a long time but it was possible with some older models and I admit that this would be helpful at work in situations when I want to see many lines of code at a glance. Though I'd like to have it autorotate like in smartphones, not to have to do it manually from the OS.

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    This is a good point. I know several people who use their secondary screens this way. – user.S Dec 10 '18 at 16:59
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    Not just in the past. Monitors can still do this! – Sean Dec 11 '18 at 3:52
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    It's also nice for writing (non-code). You get one sheet of paper on the screen in its entirety. No need to scroll. – henning -- reinstate Monica Dec 11 '18 at 11:21
  • @Sean didn't know that. I haven't seen any models coming out of the factory with that feature lately. Only mounts that you can buy separately. – memory of a dream Dec 19 '18 at 15:01
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I know probably not many do this, but for some time that I had my desktop monitor close to where my head's at in bed, I would rotate the screen so I could read or watch a movie while laying on my side. I've also done that with my laptop a few times.

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    Indeed not common enough for the window manager to by default be programmed to do this, so a nice anecdote but not answering the question at all. [Indeed the auto-rotating from tablets and phones annoy me in exactly this situation, setting rotation-lock is quickly learned.] – user3445853 Dec 10 '18 at 13:49
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    @user3445853 Well, it is a use-case, so I would argue it is an answer. Who knows, it may be that the first person to implement screen rotation was also in a similar scenario as me with his CRT monitor. :P As for window managers being programmed, I think Windows has default keybindings for this, and in Unix based OSes, any decent window manager will allow you to set keybindings for commands. It's just a matter of configuring one to do xrandr --output $output --rotate right. There is no need for the window manager to "program" it. – JoL Dec 10 '18 at 16:08
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For whom is this feature created?

Originally created? Probably tabletop arcade gamers. Two-player ftw.

enter image description here

If you look carefully, you can see player controls on both sides of the image under the glass (red joystick on the left, blue button on the right). While it's player 1's turn, player 2 watches (upside down). When player 1 loses a life, the screen flips so player 2's view is the correct way 'round.

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    Ahhhhhh wow that makes a lot of sense – Lynob Dec 10 '18 at 9:51
  • Also (still) a thing for TTRPGs: hackaday.com/2018/02/20/dungeons-and-dragons-tv-tabletop – user922589 Dec 10 '18 at 11:42
  • I don't get it. Would the players take turns? Otherwise, if they're both playing at the same time, when would the screen be rotated? – JoL Dec 10 '18 at 16:17
  • Yes, it's for players taking turns. – Cupcake Protocol Dec 10 '18 at 23:33
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The short answer probably is: Because not all display devices are able to correctly report their orientation.

Off the top of my head, I can imagine the following use cases for being able to flip/mirror/rotate the screen orientation:

  • Projector hanging from the ceiling: 180° rotation.
  • Standard projector used to project on the back of a screen to shine through it: mirror horizontally.
  • Display in portrait mode: 90° rotation left or right (I'm using such a setup right now, and it seems like the display does not report its orientation to the OS: I had to configure that myself).
  • Convertible Laptop: I've been using a convertible laptop in the mid-2000s, which did not have a sensor to determine the orientation. Instead, I configured some additional keys so I could rotate the display in software with one click.

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