Grid Viewports             package: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))
     }

