R: Create a Grid Viewport

Grid Viewports {grid} | R Documentation

## Create a Grid Viewport

### Description

These functions create viewports, which describe rectangular regions on a graphics device and define a number of coordinate systems within those regions.

### Usage

    viewport(x = unit(0.5, "npc"), y = unit(0.5, "npc"),
             width = unit(1, "npc"), height = unit(1, "npc"),
             default.units = "npc", just = "centre",
             gp = gpar(), clip = "inherit",
             xscale = c(0, 1), yscale = c(0, 1),
             angle = 0,
             layout = NULL,
             layout.pos.row = NULL, layout.pos.col = NULL,
             name = NULL)
    vpList(...)
    vpStack(...)
    vpTree(parent, children)

### Arguments

`x` | A numeric vector or unit object specifying x-location.
`y` | A numeric vector or unit object specifying y-location.
`width` | A numeric vector or unit object specifying width.
`height` | A numeric vector or unit object specifying height.
`default.units` | A string indicating the default units to use if `x`, `y`, `width`, or `height` are only given as numeric vectors.
`just` | A string or numeric vector specifying the justification of the viewport relative to its (x, y) location. If there are two values, the first value specifies horizontal justification and the second value specifies vertical justification. Possible string values are: `"left"`, `"right"`, `"centre"`, `"center"`, `"bottom"`, and `"top"`. For numeric values, 0 means left alignment and 1 means right alignment.
`gp` | An object of class `gpar`, typically the output from a call to the function `gpar`. This is basically a list of graphical parameter settings.
`clip` | One of `"on"`, `"inherit"`, or `"off"`, indicating whether to clip to the extent of this viewport, inherit the clipping region from the parent viewport, or turn clipping off altogether. For back-compatibility, a logical value of `TRUE` corresponds to `"on"` and `FALSE` corresponds to `"inherit"`.
`xscale` | A numeric vector of length two indicating the minimum and maximum on the x-scale.
`yscale` | A numeric vector of length two indicating the minimum and maximum on the y-scale.
`angle` | A numeric value indicating the angle of rotation of the viewport. Positive values indicate the amount of rotation, in degrees, anticlockwise from the positive x-axis.
`layout` | A Grid layout object which splits the viewport into subregions.
`layout.pos.row` | A numeric vector giving the rows occupied by this viewport in its parent's layout.
`layout.pos.col` | A numeric vector giving the columns occupied by this viewport in its parent's layout.
`name` | A character value to uniquely identify the viewport once it has been pushed onto the viewport tree.
`...` | Any number of grid viewport objects.
`parent` | A grid viewport object.
`children` | A vpList object.

### Details

The location and size of a viewport are relative to the coordinate systems defined by the viewport's parent (either a graphical device or another viewport). The location and size can be specified in a very flexible way by specifying them with unit objects. When specifying the location of a viewport, specifying both `layout.pos.row` and `layout.pos.col` as `NULL` indicates that the viewport ignores its parent's layout and specifies its own location and size (via its `locn`). If only one of `layout.pos.row` and `layout.pos.col` is `NULL`, this means occupy ALL of the appropriate row(s)/column(s). For example, `layout.pos.row = 1` and `layout.pos.col = NULL` means occupy all of row 1. Specifying non-`NULL` values for both `layout.pos.row` and `layout.pos.col` means occupy the intersection of the appropriate rows and columns. If a vector of length two is specified for `layout.pos.row` or `layout.pos.col`, this indicates a range of rows or columns to occupy. For example, `layout.pos.row = c(1, 3)` and `layout.pos.col = c(2, 4)` means occupy cells in the intersection of rows 1, 2, and 3, and columns, 2, 3, and 4.

Clipping obeys only the most recent viewport clip setting. For example, if you clip to viewport1, then clip to viewport2, the clipping region is determined wholly by viewport2, the size and shape of viewport1 is irrelevant (until viewport2 is popped of course).

If a viewport is rotated (because of its own `angle` setting or because it is within another viewport which is rotated) then the `clip` flag is ignored.

Viewport names need not be unique. When pushed, viewports sharing the same parent must have unique names, which means that if you push a viewport with the same name as an existing viewport, the existing viewport will be replaced in the viewport tree. A viewport name can be any string, but grid uses the reserved name `"ROOT"` for the top-level viewport. Also, when specifying a viewport name in `downViewport` and `seekViewport`, it is possible to provide a viewport path, which consists of several names concatenated using the separator (currently `::`). Consequently, it is not advisable to use this separator in viewport names.

The viewports in a `vpList` are pushed in parallel. The viewports in a `vpStack` are pushed in series. When a `vpTree` is pushed, the parent is pushed first, then the children are pushed in parallel.

### Value

An R object of class `viewport`.

### Author(s)

Paul Murrell

### See Also

Grid, `pushViewport`, `popViewport`, `downViewport`, `seekViewport`, `upViewport`, `unit`, `grid.layout`, `grid.show.layout`.

### Examples

    # Diagram of a sample viewport
    grid.show.viewport(viewport(x=0.6, y=0.6,
                       w=unit(1, "inches"), h=unit(1, "inches")))
    # Demonstrate viewport clipping
    clip.demo <- function(i, j, clip1, clip2) {
      pushViewport(viewport(layout.pos.col=i,
                             layout.pos.row=j))
      pushViewport(viewport(width=0.6, height=0.6, clip=clip1))
      grid.rect(gp=gpar(fill="white"))
      grid.circle(r=0.55, gp=gpar(col="red", fill="pink"))
      popViewport()
      pushViewport(viewport(width=0.6, height=0.6, clip=clip2))
      grid.polygon(x=c(0.5, 1.1, 0.6, 1.1, 0.5, -0.1, 0.4, -0.1),
                   y=c(0.6, 1.1, 0.5, -0.1, 0.4, -0.1, 0.5, 1.1),
                   gp=gpar(col="blue", fill="light blue"))
      popViewport(2)
    }

    grid.newpage()
    grid.rect(gp=gpar(fill="grey"))
    pushViewport(viewport(layout=grid.layout(2, 2)))
    clip.demo(1, 1, FALSE, FALSE)
    clip.demo(1, 2, TRUE, FALSE)
    clip.demo(2, 1, FALSE, TRUE)
    clip.demo(2, 2, TRUE, TRUE)
    popViewport()
    # Demonstrate turning clipping off
    grid.newpage()
    pushViewport(viewport(w=.5, h=.5, clip="on"))
    grid.rect()
    grid.circle(r=.6, gp=gpar(lwd=10))
    pushViewport(viewport(clip="inherit"))
    grid.circle(r=.6, gp=gpar(lwd=5, col="grey"))
    pushViewport(viewport(clip="off"))
    grid.circle(r=.6)
    popViewport(3)
    # Demonstrate vpList, vpStack, and vpTree
    grid.newpage()
    tree <- vpTree(viewport(w=0.8, h=0.8, name="A"),
                   vpList(vpStack(viewport(x=0.1, y=0.1, w=0.5, h=0.5,
                                           just=c("left", "bottom"), name="B"),
                                  viewport(x=0.1, y=0.1, w=0.5, h=0.5,
                                           just=c("left", "bottom"), name="C"),
                                  viewport(x=0.1, y=0.1, w=0.5, h=0.5,
                                           just=c("left", "bottom"), name="D")),
                          viewport(x=0.5, w=0.4, h=0.9,
                                   just="left", name="E")))
    pushViewport(tree)
    for (i in LETTERS[1:5]) {
      seekViewport(i)
      grid.rect()
      grid.text(current.vpTree(FALSE),
                x=unit(1, "mm"), y=unit(1, "npc") - unit(1, "mm"),
                just=c("left", "top"),
                gp=gpar(fontsize=8))
    }

[Package grid version 2.8.1 Index]