RandR
Encyclopedia
The X Resize, Rotate and Reflect Extension (RandR) is a X Window System
extension, which allows clients to dynamically change X screens, so as to resize, rotate and reflect the root window of a screen. The initial X11 design did not anticipate the need for dynamic resizing and it was necessary to restart the X server to bring about the changes. However, changing the screen resolution on the fly without changing the desktop size had been available under XFree86
since the beginning. RandR extension framework brought the ability to change display characteristics without restarting the X session. The extension framework allows laptops and handheld computers to change their screen size to drive external monitors at different resolutions
than their built in screens.
If one's desktop environment
doesn't provide a graphical tool for interfacing with this functionality, the xrandr command line tool may be used.
(q.v.) has nuanced usage of a number of terms when compared to common usage, particularly "display" and "screen", a subset of which is given here for convenience:
device: A graphics device such as a computer graphics card or a computer motherboard's integrated graphics chipset.
monitor: A physical device such as a CRT
or a flat screen computer display.
screen: An area into which graphics may be rendered, either through software alone into RAM
as with VNC, or within a graphics device, some of which support rendering into more than one screen simultaneously, either viewable simultaneously or interchangeably. Interchangeable screens are often set up to be notionally left and right from one another, flipping from one to the next as the mouse pointer reaches the edge of the monitor.
virtual screen: Two different meanings are associated with this term:
display: A collection of screens, often involving multiple monitors, generally configured to allow the mouse to move the pointer to any position within them. Linux
-based workstations usually support having multiple displays, which are switched by special keyboard combinations such as control-alt-function-key, simultaneously flipping all the monitors from showing the screens of one display to the screens in another.
The term "display" should not be confused with the more specialized jargon "Zaphod display". The latter is a rare configuration allowing multiple users of a single computer to each have an independent set of display, mouse, and keyboard, as though they were using separate computers, but at a lower per-seat cost.
One practical limiting effect of this is that it is not possible to run a different WM
on each monitor, since window managers are limited to one per screen.
Some of these specific issues are resolved in RandR 1.3, but the Xorg Foundation has been criticised for removing useful, and widely used, functionality before an effective substitute is available.
1.4 does not contain the following:
X Window System
The X window system is a computer software system and network protocol that provides a basis for graphical user interfaces and rich input device capability for networked computers...
extension, which allows clients to dynamically change X screens, so as to resize, rotate and reflect the root window of a screen. The initial X11 design did not anticipate the need for dynamic resizing and it was necessary to restart the X server to bring about the changes. However, changing the screen resolution on the fly without changing the desktop size had been available under XFree86
XFree86
XFree86 is an implementation of the X Window System. It was originally written for Unix-like operating systems on IBM PC compatibles and is now available for many other operating systems and platforms. It is free and open source software under the XFree86 License version 1.1. It is developed by the...
since the beginning. RandR extension framework brought the ability to change display characteristics without restarting the X session. The extension framework allows laptops and handheld computers to change their screen size to drive external monitors at different resolutions
Display resolution
The display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...
than their built in screens.
If one's desktop environment
Desktop environment
In graphical computing, a desktop environment commonly refers to a style of graphical user interface derived from the desktop metaphor that is seen on most modern personal computers. These GUIs help the user in easily accessing, configuring, and modifying many important and frequently accessed...
doesn't provide a graphical tool for interfacing with this functionality, the xrandr command line tool may be used.
Key terms
The X window systemX Window System
The X window system is a computer software system and network protocol that provides a basis for graphical user interfaces and rich input device capability for networked computers...
(q.v.) has nuanced usage of a number of terms when compared to common usage, particularly "display" and "screen", a subset of which is given here for convenience:
device: A graphics device such as a computer graphics card or a computer motherboard's integrated graphics chipset.
monitor: A physical device such as a CRT
CRT
-Medicine:* Capillary refill time, the rate at with blood refills empty capillaries* Cognitive Retention Therapy, a dementia treatment* Cardiac resynchronization therapy, a treatment for heart failure** CRT-D, an implanted cardiac resynchronization device...
or a flat screen computer display.
screen: An area into which graphics may be rendered, either through software alone into RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
as with VNC, or within a graphics device, some of which support rendering into more than one screen simultaneously, either viewable simultaneously or interchangeably. Interchangeable screens are often set up to be notionally left and right from one another, flipping from one to the next as the mouse pointer reaches the edge of the monitor.
virtual screen: Two different meanings are associated with this term:
- A technique allowing panning a monitor around a screen running at a larger resolution than the monitor is currently displaying.
- An effect simulated by a window manager by maintaining window position information in a larger coordinate system than the screen and allowing panning by simply moving the windows in response to the user.
display: A collection of screens, often involving multiple monitors, generally configured to allow the mouse to move the pointer to any position within them. Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
-based workstations usually support having multiple displays, which are switched by special keyboard combinations such as control-alt-function-key, simultaneously flipping all the monitors from showing the screens of one display to the screens in another.
The term "display" should not be confused with the more specialized jargon "Zaphod display". The latter is a rare configuration allowing multiple users of a single computer to each have an independent set of display, mouse, and keyboard, as though they were using separate computers, but at a lower per-seat cost.
RandR 1.2
RandR 1.2 only permits one virtual screen per display device. It is not possible to assign each monitor on a device to a different screen (sometimes called "Zaphod" mode), or to combine monitors from multiple devices into a single screen.One practical limiting effect of this is that it is not possible to run a different WM
Window manager
A window manager is system software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment...
on each monitor, since window managers are limited to one per screen.
Some of these specific issues are resolved in RandR 1.3, but the Xorg Foundation has been criticised for removing useful, and widely used, functionality before an effective substitute is available.
RandR 1.3
Some of the features in version 1.3:- querying state without output probing
- multi-monitor panning (still limited to one separate screen per GPU)
- display transformations (translation, scaling, rotation, projection)
- support for standard outputs
RandR 1.4
Some of the proposed features in 1.4:- Per-CRTC pixmaps for providing multiple scan-out buffers.
- Support for sprite position and image transforms.
- Request change for CRTC configurations (to reduce screen flickering and allow NVIDIA to implement RandR 1.2 support in the binary driver)
1.4 does not contain the following:
- Per-output DPMS controls
- Multi-GPU improvements