gpar: Handling Grid Graphical Parameters

Description

gpar() should be used to create a set of graphical parameter settings. It returns an object of class "gpar". This is basically a list of name-value pairs. get.gpar() can be used to query the current graphical parameter settings.

Usage

gpar(...)
get.gpar(names = NULL)

Arguments

…

Any number of named arguments.

names

A character vector of valid graphical parameter names.

Value

An object of class "gpar".

Details

All grid viewports and (predefined) graphical objects have a slot called gp, which contains a "gpar" object. When a viewport is pushed onto the viewport stack and when a graphical object is drawn, the settings in the "gpar" object are enforced. In this way, the graphical output is modified by the gp settings until the graphical object has finished drawing, or until the viewport is popped off the viewport stack, or until some other viewport or graphical object is pushed or begins drawing. The default parameter settings are defined by the ROOT viewport, which takes its settings from the graphics device. These defaults may differ between devices (e.g., the default fill setting is different for a PNG device compared to a PDF device). Valid parameter names are:

col	Colour for lines and borders.
fill	Colour for filling rectangles, polygons, ...
alpha	Alpha channel for transparency
lty	Line type
lwd	Line width
lex	Multiplier applied to line width
lineend	Line end style (round, butt, square)
linejoin	Line join style (round, mitre, bevel)
linemitre	Line mitre limit (number greater than 1)
fontsize	The size of text (in points)
cex	Multiplier applied to fontsize
fontfamily	The font family
fontface	The font face (bold, italic, ...)
lineheight	The height of a line as a multiple of the size of text
font	Font face (alias for fontface; for backward compatibility)

For more details of many of these, see the help for the corresponding graphical parameter par in base graphics. (This may have a slightly different name, e.g. lend, ljoin, lmitre, family.) Colours can be specified in one of the forms returned by rgb, as a name (see colors) or as a non-negative integer index into the current palette (with zero being taken as transparent). (Negative integer values are now an error.) The alpha setting is combined with the alpha channel for individual colours by multiplying (with both alpha settings normalised to the range 0 to 1). The size of text is fontsize*cex. The size of a line is fontsize*cex*lineheight. The cex setting is cumulative; if a viewport is pushed with a cex of 0.5 then another viewport is pushed with a cex of 0.5, the effective cex is 0.25. The alpha and lex settings are also cumulative. Changes to the fontfamily may be ignored by some devices, but is supported by PostScript, PDF, X11, Windows, and Quartz. The fontfamily may be used to specify one of the Hershey Font families (e.g., HersheySerif) and this specification will be honoured on all devices. The specification of fontface can be an integer or a string. If an integer, then it follows the R base graphics standard: 1 = plain, 2 = bold, 3 = italic, 4 = bold italic. If a string, then valid values are: "plain", "bold", "italic", "oblique", and "bold.italic". For the special case of the HersheySerif font family, "cyrillic", "cyrillic.oblique", and "EUC" are also available. All parameter values can be vectors of multiple values. (This will not always make sense -- for example, viewports will only take notice of the first parameter value.) get.gpar() returns all current graphical parameter settings.

Examples

Run this code

gp <- get.gpar()
utils::str(gp)
## These *do* nothing but produce a "gpar" object:
gpar(col = "red")
gpar(col = "blue", lty = "solid", lwd = 3, fontsize = 16)
get.gpar(c("col", "lty"))
grid.newpage()
vp <- viewport(w = .8, h = .8, gp = gpar(col="blue"))
grid.draw(gTree(children=gList(rectGrob(gp = gpar(col="red")),
                     textGrob(paste("The rect is its own colour (red)",
                                    "but this text is the colour",
                                    "set by the gTree (green)",
                                    sep = "\n"))),
      gp = gpar(col="green"), vp = vp))
grid.text("This text is the colour set by the viewport (blue)",
          y = 1, just = c("center", "bottom"),
          gp = gpar(fontsize=20), vp = vp)
grid.newpage()
## example with multiple values for a parameter
pushViewport(viewport())
grid.points(1:10/11, 1:10/11, gp = gpar(col=1:10))
popViewport()