RandR

The X Resize, Rotate and Reflect Extension (RandR)^[2] is an 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 display server to bring about the changes. However, XFree86 has, since its first release, supported changing the screen resolution on the fly without changing the desktop size. 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.^[3]

If one's desktop environment does not provide a graphical tool for interfacing with this functionality, the xrandr command line tool may be used.

Key terms

The X window system 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:

• 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-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.

Limitations and criticisms of RandR

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.^[4] 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.^[5]

Release history

RandR 1.3

Some of the features in version 1.3:^[6]

• Querying state without output probing
• Multi-monitor panning (still limited to one separate screen per GPU^[7])
• Display transformations (translation, scaling, rotation, projection)
• Support for standard outputs

RandR 1.4

Some of the features in 1.4:^[8]

• Output border adjustment properties
• Provider objects, which allow configuration of render and output offload for multi-GPU configurations

References

External links

• XRandR project page at X.org
• The X Resize, Rotate and Reflect Extension

v t e X Window System Architecture Core protocol X Window selection X Toolkit Intrinsics X Window authorization X11 color names Wayland Extensions X Image Extension X keyboard extension RandR X Rendering Extension Shape extension Shared memory extension X Display Manager Control Protocol X video extension X-Video Motion Compensation AIGLX GLX Multi-Pointer X Display PostScript Components and notable implementations display servers X.Org Server Cygwin/X XQuartz X-Win32 X386 XFree86 XGGI XDarwin Xming Xsgi Xsun Xgl Xnest Xephyr client libraries Xlib XCB display managers session managers GDM KDM XDM LightDM LXDM SLiM Entrance WDM window managers Compositing Compiz KWin Metacity Mutter Xfwm Tiling awesome dwm i3 Ion PWM ratpoison wmii xmonad Stacking AfterStep amiwm Blackbox cwm Enlightenment Fluxbox FVWM IceWM JWM Matchbox mwm Openbox PekWM Sawfish twm Window Maker Re-parenting most of the above Standards ICCCM EWMH XDS freedesktop.org Applications xcalc xclock xedit xload xterm xeyes desktop environments