Why is it possible to flip the screen?

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?

Lynob

Posted 2018-12-09T11:07:04.903

Reputation: 3 254

174It's necessary for users ɐıʃɐɹʇsn∀ uı – bmargulies – 2018-12-09T19:17:29.330

14I was reading color inversion until I arrived at the words rotate sideways. – Chris – 2018-12-09T22:08:39.393

14A 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 – 2018-12-09T22:30:49.160

3This is very handy with projectors. – TLW – 2018-12-10T01:41:05.993

15@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 – 2018-12-10T01:41:45.817

1@Peter Would hardware only rotation be compatible with things which address individual subpixels, like ClearType? You at least need some sort of notification that subpixel ordering is changed from display. – user364455 – 2018-12-10T04:13:27.590

1@TLW the claim that having the feature in the OS doesn't hurt contradicts the first sentence of the question you're commenting on. – Peter – 2018-12-10T07:44:15.203

9With "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 – 2018-12-10T13:45:19.387

@user3445853 I didn't say "flip" I said "invert" but my question was edited and so the word flip was used – Lynob – 2018-12-10T13:48:01.207

@Peter That would only make sense if there were only square monitors. For rectangular monitors the programs running need to know of the new dimensions to redraw their content accordingly. – JoL – 2018-12-10T20:29:50.023

@user3445853 Mirroring a display would be useful for rear-mounted projectors. (i.e. Where the projector is behind the screen.) It would also work for when the projector is being reflected off of a mirror. – Abion47 – 2018-12-10T22:15:15.407

I'm not sure why this is closed as opinion-based. – Herohtar – 2018-12-11T16:31:30.933

@TLW you can say the same about any feature, it doesn't make the feature legit – Askar Kalykov – 2018-12-12T19:09:44.697

Answers

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:

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.

user.S

Posted 2018-12-09T11:07:04.903

Reputation: 763

1I would have thought that an inverted screen on a tablet computer is a feature, not something that needs to be fixed as noted in the question. The projector aspect is one I hadn't thought of, yet had to use during an assist at the library! Dying brain cells. – fred_dot_u – 2018-12-09T16:55:31.537

The thing with the computer is that you need to be able to turn the screen depending on what mode you're using it in. One way in ordinary laptop mode. Another in this tablet mode. You can see that the text "Lenovo" is upside down because of it. – user.S – 2018-12-09T17:04:32.690

17You 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 – 2018-12-09T20:13:24.800

17To 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 – 2018-12-09T20:53:51.400

3@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 – 2018-12-10T01:43:33.460

10@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 – 2018-12-10T01:44:09.447

Don't forget handheld devices, such as tablets, that run Windows 10. – Ismael Miguel – 2018-12-10T02:47:28.697

@LightnessRacesinOrbit the way I remember "e.g." vs "i.e." is the former similar to "eggsample" - a non-exhaustive list. There was a counterpart to memorize "i.e." (an exhaustive list), but "eggsample" is what stuck in my mind – VLAZ – 2018-12-10T07:48:35.597

2Some 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 – 2018-12-10T09:35:54.283

1The projector reason really ought to be at the top of the answer, as that is "the" reason screen flip is possible. Tablets and such (especially like the one in the photo) auto-rotate when you flip them, as it would be a major hassle to have to go into settings to flip your screen every time you wanted to go from tablet to laptop mode. – Herohtar – 2018-12-10T16:55:54.763

@Herohtar they do auto-rotate, but by using an accelerometer to instruct the drivers. And manual override is useful – Chris H – 2018-12-11T11:05:24.833

@Stese I figured out a way to automate mine with a microswitch and a USB-GPIO board, but then found that I didn't get on with portrait mode anyway, despite having paid extra for the mount you describe. – Chris H – 2018-12-11T11:06:38.393

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.

Charlie Harding

Posted 2018-12-09T11:07:04.903

Reputation: 766

13+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 – 2018-12-09T19:39:13.367

2Wow that's so smart – Lynob – 2018-12-09T20:41:53.630

10@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 – 2018-12-10T01:51:08.047

2@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 – 2018-12-10T09:46:05.417

@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 – 2018-12-10T14:26:14.723

@AustinHemmelgarn Ok, now I think I understand what you mean. But did they really use the same CRTs for computer monitors as for TVs? I would have thought that the specs were quite different? And even if they used the same the same CRTs, what would be the reason that they couldn't have changed the orientation when they used them for computer monitors? – jkej – 2018-12-10T14:37:46.813

@jkej It wasn't originally exactly the same CRT's as used in TV's (see for example the oldest text terminals) but things quickly moved that way when color displays were desired for computers. As far as why they couldn't rotate the displays, the biggest issue was mounting (CRT's are heavy and difficult to mount, so mounts rarely let you rotate them), though some systems (such as the Asteroids arcade machines) did mount them sideways. The big issue is that it doesn't really change your screen shape enough to matter with a 4:3 CRT, the aspect ratio is too close to give you extra vertical space. – Austin Hemmelgarn – 2018-12-10T15:04:52.097

@AustinHemmelgarn What I meant was that they could have built computer monitors specifically for portrait viewing (with mounts designed only for portrait viewing) and still used the same CRTs as for TVs, if this had been desirable. After reading this question, I think it's more likely that the driving force for landscape orientation in computer monitors was the difficulty in displaying the 80 character line standard with good legibility in portrait orientation on the lower resolutions typically used at that time.

– jkej – 2018-12-10T15:48:01.757

@jkej Ah, sorry I misunderstood. Your point about the predominance of text mode and the challenges of displaying that on a portrait orientation is a good one I hadn't thought of. I'd be willing to bet that cost was another big factor though, the Alto's display was really expensive even back then because making long rectangular CRT's like that is hard, so it would not surprise me if most companies didn't think it was worth the cost because of general lack of interest. – Austin Hemmelgarn – 2018-12-10T16:12:27.840

@jkej It's not just video viewing, really. Portrait is great for documents and reading, but landscape is good for pretty much everything else - especially databases of any kind (including table processors like Excel). Even for documents, it's pretty handy to have extra space on the sides for tools when you're editing documents or really interacting with them in any way (e.g. making notes by the side). Don't forget that human field of view is much wider than it is tall - reading ("portrait") is the special case (for many wildly different reasons, most of which only apply to western scripts). – Luaan – 2018-12-11T10:20:54.560

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.

fred_dot_u

Posted 2018-12-09T11:07:04.903

Reputation: 1 377

8I'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 – 2018-12-10T08:59:41.890

Beakers are often mounted upside down, however they usually feature a facility to flip the input signal themselves – eckes – 2018-12-10T11:07:23.573

1@eckes If you mount a beaker upside down, wouldn't whatever liquid you put in it just fall out? – Glen Yates – 2018-12-10T18:10:07.947

Beamer of course ;) – eckes – 2018-12-10T19:30:03.570

@eckes the strange thing is that hardly anyone outside Germany uses "Beamer" to mean projector - but Beamer comes from English – Chris H – 2018-12-11T11:09:06.557

Yeah we do have our own English, like Handy and Public Viewing — was not aware that Beamer is also such a false friend. Thanks for the note – eckes – 2018-12-11T11:15:02.837

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.)

Aganju

Posted 2018-12-09T11:07:04.903

Reputation: 9 103

1The 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 – 2018-12-10T13:52:23.097

4@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 – 2018-12-10T18:38:45.450

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.

memory of a dream

Posted 2018-12-09T11:07:04.903

Reputation: 191

3This is a good point. I know several people who use their secondary screens this way. – user.S – 2018-12-10T16:59:33.533

4Not just in the past. Monitors can still do this! – Sean – 2018-12-11T03:52:12.840

1It'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 – 2018-12-11T11:21:30.520

@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 – 2018-12-19T15:01:54.840

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.

JoL

Posted 2018-12-09T11:07:04.903

Reputation: 332

2Indeed 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 – 2018-12-10T13:49:50.080

1@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 – 2018-12-10T16:08:48.670

For whom is this feature created?

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

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.

mcalex

Posted 2018-12-09T11:07:04.903

Reputation: 2 315

2Ahhhhhh wow that makes a lot of sense – Lynob – 2018-12-10T09:51:48.597

Also (still) a thing for TTRPGs: https://hackaday.com/2018/02/20/dungeons-and-dragons-tv-tabletop/

– None – 2018-12-10T11:42:14.293

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 – 2018-12-10T16:17:57.450

Yes, it's for players taking turns. – Cupcake Protocol – 2018-12-10T23:33:12.550

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.

orithena

Posted 2018-12-09T11:07:04.903

Reputation: 156