Handling Grid Graphical Parameters
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.
gpar(...) get.gpar(names = NULL)
Any number of named arguments.
A character vector of valid graphical parameter names.
All grid viewports and (predefined) graphical objects have a slot
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
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|
|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
par in base graphics. (This may
have a slightly different name, e.g.
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
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
cex. The size of a line
cex setting is cumulative; if a viewport is pushed
cex of 0.5 then another viewport is pushed with a
cex of 0.5, the effective
cex is 0.25.
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.,
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:
For the special case of the HersheySerif font family,
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.
An object of class
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()