R: Create Grid Graphical Objects, aka "Grob"s

grid.grob {grid} | R Documentation

## Create Grid Graphical Objects, aka "Grob"s

### Description

Creating grid graphical objects, short (“grob”s).

`grob()` and `gTree()` are the basic creators, `grobTree()` and `gList()` take several grobs to build a new one.

### Usage

    ## Grob Creation:

    grob (..., name = NULL, gp = NULL, vp = NULL, cl = NULL)
    gTree(..., name = NULL, gp = NULL, vp = NULL, children = NULL,
          childrenvp = NULL, cl = NULL)
    grobTree(..., name = NULL, gp = NULL, vp = NULL,
             childrenvp = NULL, cl = NULL)
    gList(...)

    ## Grob Properties:
    childNames(gTree)
    is.grob(x)

### Arguments

`...` | For `grob` and `gTree`, the named slots describing important features of the graphical object. For `gList` and `grobTree`, a series of grob objects.
`name` | a character identifier for the grob. Used to find the grob on the display list and/or as a child of another grob.
`children` | a `"gList"` object.
`childrenvp` | a `viewport` object (or `NULL`).
`gp` | A gpar object, typically the output from a call to the function `gpar`. This is basically a list of graphical parameter settings.
`vp` | a `viewport` object (or `NULL`).
`cl` | string giving the class attribute for the new class.
`gTree` | a `"gTree"` object.
`x` | An R object.

### Details

These functions can be used to create a basic `"grob"`, `"gTree"`, or `"gList"` object, or a new class derived from one of these.

A grid graphical object (“grob”) is a description of a graphical item. These basic classes provide default behaviour for validating, drawing, and modifying graphical objects. Both `grob()` and `gTree()` call the function `validDetails` to check that the object returned is internally coherent.

A `"gTree"` can have other grobs as children; when a gTree is drawn, it draws all of its children. Before drawing its children, a gTree pushes its `childrenvp` slot and then navigates back up (calls `upViewport`) so that the children can specify their location within the `childrenvp` via a `vpPath`.

Grob names need not be unique in general, but all children of a gTree must have different names. A grob name can be any string, though it is not advisable to use the `gPath` separator (currently `::`) in grob names.

The function `childNames` returns the names of the grobs which are children of a gTree.

All grid primitives (`grid.lines`, `grid.rect`, ...) and some higher-level grid components (e.g., `grid.xaxis` and `grid.yaxis`) are derived from these classes.

`grobTree` is just a convenient wrapper for `gTree` when the only components of the gTree are grobs (so all unnamed arguments become children of the gTree).

The `grid.grob` function is defunct.

### Value

An R object of class `"grob"`, a graphical object.

### Author(s)

Paul Murrell

### See Also

`grid.draw`, `grid.edit`, `grid.get`.

[Package grid version 3.1.2 Index]