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murrell |
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% File src/library/grid/man/makeContent.Rd
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ripley |
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% Part of the R package, https://www.R-project.org
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murrell |
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% Copyright 1995-2007 R Core Team
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% Distributed under GPL 2 or later
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\name{makeContent}
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\alias{makeContent}
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\alias{makeContext}
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\title{ Customised grid Grobs }
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\description{
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These generic hook functions are called whenever a grid grob is drawn.
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They provide an opportunity for customising the drawing context
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and drawing content of a
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new class derived from grob (or gTree).
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}
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\usage{
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makeContext(x)
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makeContent(x)
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}
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\arguments{
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\item{x}{ A grid grob. }
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}
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\details{
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These functions are called by the \code{grid.draw} methods for grobs
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and gTrees.
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ripley |
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\code{makeContext} is called first during the drawing of a grob.
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This function should be used to \emph{modify} the \code{vp} slot
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of \code{x} (and/or the \code{childrenvp} slot if \code{x}
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is a gTree). The function \emph{must} return the modified \code{x}.
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Note that
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the default behaviour for grobs is to push any viewports in the
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\code{vp} slot, and for gTrees is to also push and up any viewports in the
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\code{childrenvp} slot, so this function is used to customise the
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drawing context for a grob or gTree.
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ripley |
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murrell |
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\code{makeContent} is called next and is where any additional
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calculations should occur and graphical content should
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be generated (see, for example,
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\code{grid:::makeContent.xaxis}).
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murrell |
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This function should be used to \emph{modify} the \code{children}
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of a gTree.
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The function \emph{must} return the modified \code{x}.
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Note that the default behaviour
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for gTrees is to draw all grobs in the \code{children} slot,
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so this function is used to customise the drawing content for a gTree.
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It is also possible to customise the drawing content for a simple
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grob, but more care needs to be taken; for example, the function
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should return a standard grid primitive with a \code{drawDetails()}
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method in this case.
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Note that these functions should be \emph{cumulative} in their
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effects, so that the \code{x} returned by \code{makeContent()}
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\emph{includes} any changes made by \code{makeContext()}.
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Note that \code{makeContext} is
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also called in the calculation of \code{"grobwidth"} and
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\code{"grobheight"} units.
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}
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\value{
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Both functions are expected to return a grob or gTree
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(a modified version of \code{x}).
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}
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\author{ Paul Murrell }
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\seealso{ \code{\link{grid.draw}} }
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\keyword{ dplot }
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