\Header{trellis.par.get}{Graphical Parameters for Trellis Displays}
\alias{lattice.theme}{trellis.par.get}
\alias{show.settings}{trellis.par.get}
\alias{trellis.par.set}{trellis.par.get}
\keyword{dplot}{trellis.par.get}
\begin{Description}\relax
Functions used to query, display and modify graphical parameters for
fine control of Trellis displays.
\end{Description}
\begin{Usage}
\begin{verbatim}
trellis.par.get(name = NULL)
trellis.par.set(name, value, warn)
show.settings(x = NULL)
lattice.theme
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{name}] character giving the name of a component. For a list of
valid values type \code{names(trellis.par.get())}.

\item[\code{value}] a list giving the desired value of the component. 
\item[\code{warn}] logical, whether a warning should be issued when
\code{trellis.par.get} is called when no graphics device is open 
\item[\code{x}] optional list of components that change the settings (any
valid value of \code{theme} in \code{lset}). These are used to
modify the current settings (obtained by \code{trellis.par.get})
before they are displayed

\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The various graphical parameters (color, line type, background etc)
that control the look and feel of Trellis displays are highly
customizable. Also, R can produce graphics on a number of devices, and
it is expected that a different set of parameters would be more suited
to different devices. These parameters are stored in a global variable
named \code{lattice.theme}, which is a list whose components define
settings for particular devices. The components are idenified by the
name of the device they represent (as obtained by \code{.Device}), and
are created as and when new devices are opened for the first time
using \code{trellis.device} (or Lattice plots are drawn on a device
for the first time in that session).

The initial settings for each device defaults to values appropriate
for that device. In practice, this boils down to three distinct
settings, one for screen devices like \code{x11} and \code{windows},
one for black and white plots (mostly useful for \code{postscript})
and one for color printers (color \code{postcript, pdf}). 

Once a device is open, it's settings can be modified. When another
instance of the same device is opened later using
\code{trellis.device}, the settings for that device are reset to its
defaults, unless otherwise specified in the call to
\code{trellis.device}. But settings for different devices are treated
separately, i.e., opening a postscript device will not alter the x11
settings, which will remain in effect whenever an x11 device is
active.

The functions \code{trellis.par.*} are meant to be interfaces to the
global settings. They always apply on the settings for the currently
ACTIVE device.

\code{trellis.par.get}, called without any arguments, returns the full
list of settings for the active device. With the \code{name} argument
present, it returns that component only. \code{trellis.par.get} sets
the value of the \code{name} component of the current active device
settings to \code{value}.

\code{trellis.par.get} is usually used inside trellis functions to get
graphical parameters before plotting. Modifications by users via
\code{trellis.par.set} is typically done as follows:

\code{add.line <- trellis.par.get("add.line")}

\code{add.line\$col <- "red"}

\code{trellis.par.set("add.line", add.line)}

The actual list of the components in \code{trellis.settings} has not
been finalized, so I'm not attempting to list them here. The current
value can be obtained by \code{print(trellis.par.get())}. Most names
should be self-explanatory.

\code{show.settings} provides a graphical display summarizing some of
the values in the current setting.

There are some simpler alternatives that can be used to manipulate the
settings. Details can be found in the documentation for \code{lset}.
\end{Details}
\begin{Value}
\code{trellis.par.get} returns a list giving parameters for that
component. If \code{name} is missing, it returns the full list.
\end{Value}
\begin{Author}\relax
Deepayan Sarkar \email{deepayan@stat.wisc.edu}
\end{Author}
\begin{SeeAlso}\relax
\code{\Link{trellis.device}}, \code{\Link{lset}},
\code{\Link{trellis.par.get}},\code{\Link{Lattice}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
show.settings()
\end{ExampleCode}
\end{Examples}

