The R Project SVN R

% File src/library/grid/man/makeContent.Rd

% Part of the R package, https://www.R-project.org

% Copyright 1995-2025 R Core Team

% Distributed under GPL 2 or later

\name{makeContent}

\alias{makeContent}

\alias{makeContext}

\title{ Customised grid Grobs }

\description{

  These generic hook functions are called whenever a grid grob is drawn.

  They provide an opportunity for customising the drawing context

  and drawing content of a

  new class derived from grob (or \I{gTree}).

}

\usage{

makeContext(x)

makeContent(x)

}

\arguments{

  \item{x}{ A grid grob. }

}

\details{

  These functions are called by the \code{grid.draw} methods for grobs

  and \I{gTree}s.

  \code{makeContext} is called first during the drawing of a grob.

  This function should be used to \emph{modify} the \code{vp} slot

  of \code{x} (and/or the \code{childrenvp} slot if \code{x}

  is a \I{gTree}).  The function \emph{must} return the modified \code{x}.

  Note that

  the default behaviour for grobs is to push any viewports in the

  \code{vp} slot, and for \I{gTree}s is to also push and up any viewports in the

  \code{childrenvp} slot, so this function is used to customise the

  drawing context for a grob or \I{gTree}.

  \code{makeContent} is called next and is where any additional

  calculations should occur and graphical content should

  be generated (see, for example,

  \code{grid:::makeContent.xaxis}).

  This function should be used to \emph{modify} the \code{children}

  of a \I{gTree}.

  The function \emph{must} return the modified \code{x}.

  Note that the default behaviour

  for \I{gTree}s is to draw all grobs in the \code{children} slot,

  so this function is used to customise the drawing content for a \I{gTree}.

  It is also possible to customise the drawing content for a simple

  grob, but more care needs to be taken;  for example, the function

  should return a standard grid primitive with a \code{drawDetails()}

  method in this case.

  Note that these functions should be \emph{cumulative} in their

  effects, so that the \code{x} returned by \code{makeContent()}

  \emph{includes} any changes made by \code{makeContext()}.

  Note that \code{makeContext} is

  also called in the calculation of \code{"grobwidth"} and

  \code{"grobheight"} units.

}

\value{

  Both functions are expected to return a grob or \I{gTree}

  (a modified version of \code{x}).

}

\author{ Paul Murrell }

\references{

  \bibshow{R:Murrell:2013}

}

\seealso{ \code{\link{grid.draw}} }

\keyword{ dplot }