R: X Window System Graphics

x11 {grDevices} | R Documentation

## X Window System Graphics

### 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`.

The R function is a wrapper for two devices, one based on Xlib (http://en.wikipedia.org/wiki/Xlib) and one using cairographics (http://www.cairographics.org).

### Usage

    X11(display = "", width, height, pointsize, gamma, bg, canvas,
        fonts, family, 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` | gamma correction fudge factor. Colours in R are sRGB; if your monitor does not conform to sRGB, you might be able to improve things by tweaking this parameter to apply additional gamma correction to the RGB channels. By default 1 (no additional gamma 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 an opaque colour (and any alpha value will be ignored). Default `"white"`.
`fonts` | for `type = "Xlib"` only: 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’.
`family` | The default family: a length-one character string. This is primarily intended for cairo-based devices, but for `type = "Xlib"`, the `X11Fonts()` database is used to map family names to `fonts` (and this argument takes precedence over that one).
`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"`, `"cairo"`, `"nbcairo"` or `"dbcairo"`. Only the first will be available if the system was compiled without support for cairographics. The default is `"cairo"` where available except on OS X, 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"`, `"nbcairo"` and `"dbcairo"` 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.

There are three variants of the cairo-based device. `type = "nbcairo"` has no buffering. `type = "cairo"` has some buffering, and supports `dev.hold` and `dev.flush`. `type = "dbcairo"` buffers output and updates the screen about every 100ms (by default). The refresh interval can be set (in units of seconds) by e.g. `options(X11updates = 0.25)`: the value is consulted when a device is opened. Updates are only looked for every 50ms (at most), and during heavy graphics computations only every 500ms.

Which version will be fastest depends on the X11 connection and the type of plotting. You will probably want to use a buffered type unless backing store is in use on the X server (which for example it always is on OS X displays), as otherwise repainting when the window is exposed will be slow. On slow connections `type = "dbcairo"` will probably give the best performance.

Because of known problems with font selection on OS X without Pango (for example, the CRAN distribution), `type = "cairo"` is not the default there. These problems have included mixing up bold and italic (since worked around), selecting incorrect glyphs and ugly or missing symbol glyphs.

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.

The cursor shown indicates the state of the device. If quiescent the cursor is an arrow: when the locator is in use it is a crosshair cursor, and when plotting computations are in progress (and this can be detected) it is a watch cursor. (The exact cursors displayed will depend on the window manager in use.)

### 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. If `family` is supplied as an argument, the X11 font database is used to convert that, but otherwise the argument `fonts` (with default given by `X11.options`) is used.

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 cairographics-based devices work directly with font family names such as `"Helvetica"` which can be selected initially by the `family` argument and subsequently 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 via `fontconfig`) or `fontconfig` (on OS X and perhaps elsewhere). The results depend on the fonts installed on the system running R – setting the environmnent variable FC_DEBUG to 1 normally 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. At present the best rendering (including using kerning) will be achieved with TrueType fonts: see http://www.freedesktop.org/software/fontconfig/fontconfig-user.html for ways to set up your system to prefer them. The default family (`"Helvetica"`) is likely not to use kerning: alternatives which should if you have them installed are `"Arial"`, `"DejaVu Sans"` and `"Liberation Sans"` (and perhaps `"FreeSans"`). For those who prefer fonts with serifs, try `"Times New Roman"`, `"DejaVu Serif"` and `"Liberation Serif"`. To match LaTeX text, use something like `"CM Roman"`.

Problems with incorrect rendering of symbols (e.g., of `quote(pi)` and `expression(10^degree))`) 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 by preferring the URW Type 1 symbol font.

    <fontconfig>
    <match target="pattern">
      <test name="family"><string>Symbol</string></test>
      <edit name="family" mode="prepend" binding="same">
        <string>Standard Symbols L</string>
      </edit>
    </match>
    </fontconfig>

A test for this is to run at the command line `fc-match Symbol`. If that shows `symbol.ttf` that may be the Wine symbol font – use `locate symbol.ttf` to see if it is found from a directory with wine in the name.

### 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 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.

The default for `type = "Xlib"` is to use the best possible colour model for the visual of the X11 server: these days this will almost always be ‘truecolor’. 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 two 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.

The cairographics-based devices most likely only work (or work correctly) with ‘TrueColor’ visuals, although in principle this depends on the cairo installation: a warning is given if any other visual is encountered.

`type = "Xlib"` supports ‘TrueColor’, ‘PseudoColor’, ‘GrayScale’, `StaticGray` and `MonoChrome` visuals: ‘StaticColor’ and ‘DirectColor’ visuals are handled only in black/white.

### Anti-aliasing

Anti-aliasing is only supported for cairographics-based devices, and applies to both graphics and 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, which is assumed to conform to sRGB.

### See Also

`Devices`, `X11Fonts`, `savePlot`.

### Examples

    ## Not run:
    ## put something like 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)

[Package grDevices version 3.1.2 Index]