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x11 {grDevices}

X Window System Graphics
Package: 
grDevices
Version: 
R 2.12.1

Description

X11 starts a graphics device driver for the X Window System (version 11). This can only be done on machines/accounts that have access to an X server.

x11 is recognized as a synonym for X11.

Usage

X11(display = "", width, height, pointsize, gamma, bg, canvas,
    fonts, xpos, ypos, title, type, antialias)

X11.options(..., reset = FALSE)

Arguments

display
the display on which the graphics window will appear. The default is to use the value in the user's environment variable DISPLAY. This is ignored (with a warning) if an X11 device is already open on another display.
width, height
the width and height of the plotting window, in inches. If NA, taken from the resources and if not specified there defaults to 7 inches. See also ‘Resources’.
pointsize
the default pointsize to be used. Defaults to 12.
gamma
the gamma correction factor. This value is used to help ensure that the colours perceived are linearly related to RGB values (see hsv). By default 1 (default correction).
bg
colour, the initial background colour. Default "transparent".
canvas
colour. The colour of the canvas, which is visible only when the background colour is transparent. Should be a solid colour (and any alpha value will be ignored). Default "white".
fonts
X11 font description strings into which weight, slant and size will be substituted. There are two, the first for fonts 1 to 4 and the second for font 5, the symbol font. See section ‘Fonts’.
xpos, ypos
integer: initial position of the top left corner of the window, in pixels. Negative values are from the opposite corner, e.g. xpos=-100 says the top right corner should be 100 pixels from the right edge of the screen. If NA (the default), successive devices are cascaded in 20 pixel steps from the top left. See also ‘Resources’.
title
character string, up to 100 bytes. With the default, "", a suitable title is created internally. A C-style format for an integer will be substituted by the device number (see the file argument to postscript for further details). How non-ASCII titles are handled is implementation-dependent.
type
character string, one of "Xlib" (the only type prior to R 2.7.0) or "cairo" or "nbcairo". The latter two will only be available if the system was compiled with support for cairo. Default "cairo" where available, otherwise "Xlib".
antialias
for cairo types, the type of anti-aliasing (if any) to be used. One of c("default", "none", "gray", "subpixel").
reset
logical: should the defaults be reset to their defaults?
...
Any of the arguments to X11, plus colortype and maxcubesize (see section ‘Colour Rendering’).

Details

The defaults for all of the arguments of X11 are set by X11.options: the ‘Arguments’ section gives the ‘factory-fresh’ defaults.

The initial size and position are only hints, and may not be acted on by the window manager. Also, some systems (especially laptops) are set up to appear to have a screen of a different size to the physical screen.

Option type selects between two separate devices: R can be built with support for neither, type = "Xlib" or both. Where both are available, types "cairo" and "nbcairo" offer

  • antialiasing of text and lines.
  • translucent colours.
  • scalable text, including to sizes like 4.5 pt.
  • full support for UTF-8, so on systems with suitable fonts you can plot in many languages on a single figure (and this will work even in non-UTF-8 locales). The output should be locale-independent.

type = "nbcairo" is the same device as type="cairo" without buffering: which is faster will depend on the X11 connection. Both will be slower than type = "Xlib", especially on a slow X11 connection as all the rendering is done on the machine running R rather than in the X server.

All devices which use an X11 server (including the type =     "Xlib" versions of bitmap devices such as png) share internal structures, which means that they must use the same display and visual. If you want to change display, first close all such devices.

X11 Fonts

This section applies only to type = "Xlib".

An initial/default font family for the device can be specified via the fonts argument, but if a device-independent R graphics font family is specified (e.g., via par(family=) in the graphics package), the X11 device makes use of the X11 font database (see X11Fonts) to convert the R graphics font family to an X11-specific font family description.

X11 chooses fonts by matching to a pattern, and it is quite possible that it will choose a font in the wrong encoding or which does not contain glyphs for your language (particularly common in iso10646-1 fonts).

The fonts argument is a two-element character vector, and the first element will be crucial in successfully using non-Western-European fonts. Settings that have proved useful include

"-*-mincho-%s-%s-*-*-%d-*-*-*-*-*-*-*" for CJK languages and "-cronyx-helvetica-%s-%s-*-*-%d-*-*-*-*-*-*-*" for Russian.

For UTF-8 locales, the XLC_LOCALE databases provide mappings between character encodings, and you may need to add an entry for your locale (e.g. Fedora Core 3 lacked one for ru_RU.utf8).

Cairo Fonts

The cairo-based device works directly with font family names such as "Helvetica" which should be selected by par or gpar. There are mappings for the three device-independent font families, "sans" for a sans-serif font (to "Helvetica"), "serif" for a serif font (to "Times") and "mono" for a monospaced font (to "Courier").

The font selection is handled by Pango (usually) or cairo (on Mac OS X and perhaps elsewhere). Both make use of fontconfig (http://wwww.fontconfig.org) to select fonts and so the results depend on the fonts installed on the system running R -- setting the environmnent variable FC_DEBUG to 1 allows some tracing of the selection process.

This works best when high-quality scalable fonts are installed, usually in Type 1 or TrueType formats: see the “R Installation and Administration Manual” for advice on how to obtain and install such fonts. Because of known problems with font selection on Mac OS X without Pango, type="cairo" is not the default (as from R 2.11.0) unless Pango is available. These problems include mixing up bold and italic and selecting incorrect glyphs. Problems with incorrect rendering of symbols (e.g. of quote(pi)) have been seen on Linux systems which have the Wine symbol font installed---fontconfig then prefers this and misinterprets its encoding. Adding the following lines to ‘~/.fonts.conf’ or ‘/etc/fonts/local.conf’ may circumvent this problem.

     Symbol        Standard Symbols L      

Resources

The standard X11 resource geometry can be used to specify the window position and/or size, but will be overridden by values specified as arguments or non-NA defaults set in X11.options. The class looked for is R_x11. Note that the resource specifies the width and height in pixels and not in inches. See for example http://web.mit.edu/answers/xwindows/xwindows_resources.html and perhaps man X (or http://www.xfree86.org/current/X.7.html). An example line in ‘~/.Xresources’ might be

R_x11*geometry: 900x900-0+0 

which specifies a 900 x 900 pixel window at the top right of the screen.

Colour Rendering

X11 supports several ‘visual’ types, and nowadays almost all systems support ‘truecolor’ which X11 will use by default. This uses a direct specification of any RGB colour up to the depth supported (usually 8 bits per colour). Other visuals make use of a palette to support fewer colours, only grays or even only black/white. The palette is shared between all X11 clients, so it can be necessary to limit the number of colours used by R.

Cairo-based devices currently support only ‘truecolor’ visuals. (Cairo 1.6 will support other visuals.)

The default for type="Xlib" is to use the best possible colour model for the visual of the X11 server. This can be overridden by the colortype argument of X11.options. Note: All X11 and type = "Xlib" bmp, jpeg, png and tiff devices share a colortype which is set when the first device to be opened. To change the colortype you need to close all open such devices, and then use X11.options(colortype=).

The colortype types are tried in the order "true", "pseudo", "gray" and "mono" (black or white only). The values "pseudo" and "pseudo.cube" provide colour strategies for a pseudocolor visual. The first strategy provides on-demand colour allocation which produces exact colours until the colour resources of the display are exhausted (when plotting will fail). The second allocates (if possible) a standard colour cube, and requested colours are approximated by the closest value in the cube.

With colortype equal to "pseudo.cube" or "gray" successively smaller palettes are tried until one is completely allocated. If allocation of the smallest attempt fails the device will revert to "mono". For "gray" the search starts at 256 grays for a display with depth greater than 8, otherwise with half the available colours. For "pseudo.cube" the maximum cube size is set by X11.options(maxcolorsize=) and defaults to 256. With that setting the largest cube tried is 4 levels each for RGB, using 64 colours in the palette.

Anti-aliasing

Anti-aliasing is only supported for cairo-based devices, and applies to graphics and to fonts. It is generally preferable for lines and text, but can lead to undesirable effects for fills, e.g. for image plots, and so is never used for fills.

antialias = "default" is in principle platform-dependent, but seems most often equivalent to antialias = "gray".

Conventions

This section describes the implementation of the conventions for graphics devices set out in the “R Internals Manual”.

  • The default device size is 7 inches square.
  • Font sizes are in big points.
  • The default font family is Helvetica.
  • Line widths in 1/96 inch, minimum one pixel for type =       "Xlib", 0.01 otherwise.
  • For type = "Xlib" circle radii are in pixels with minimum one.
  • Colours are interpreted by the X11 server, normally in a fair approximation to sRGB.

See Also

Devices, X11Fonts, savePlot.

Examples

## Not run:
## put something this is your .Rprofile to customize the defaults
setHook(packageEvent("grDevices", "onLoad"),
        function(...) grDevices::X11.options(width=8, height=6, xpos=0,
                                             pointsize=10))
## End(Not run)

Documentation reproduced from R 2.12.1. License: GPL-2.