makeContent: 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 gTree).Usage
makeContext(x)
makeContent(x)
Value
Both functions are expected to return a grob or gTree
(a modified version of x).Details
These functions are called by the grid.draw methods for grobs
and gTrees. makeContext is called first during the drawing of a grob.
This function should be used to modify the vp slot
of x (and/or the childrenvp slot if x
is a gTree). The function must return the modified x.
Note that
the default behaviour for grobs is to push any viewports in the
vp slot, and for gTrees is to also push and up any viewports in the
childrenvp slot, so this function is used to customise the
drawing context for a grob or gTree. makeContent is called next and is where any additional
calculations should occur and graphical content should
be generated (see, for example,
grid:::makeContent.xaxis.
This function should be used to modify the children
of a gTree.
The function must return the modified x.
Note that the default behaviour
for gTrees is to draw all grobs in the children slot,
so this function is used to customise the drawing content for a 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 drawDetails()
method in this case. Note that these functions should be cumulative in their
effects, so that the x returned by makeContent()
includes any changes made by makeContext(). Note that makeContext is
also called in the calculation of "grobwidth" and
"grobheight" units.