Draw a Path

Description

These functions create and draw one or more paths. The final point of a path will automatically be connected to the initial point.

Usage

pathGrob(x, y,
         id=NULL, id.lengths=NULL,
         pathId=NULL, pathId.lengths=NULL,
         rule="winding",
         default.units="npc",
         name=NULL, gp=gpar(), vp=NULL)
grid.path(...)

Arguments

Details

Both functions create a path grob (a graphical object describing a path), but only grid.path draws the path (and then only if draw is TRUE).

A path is like a polygon except that the former can contain holes, as interpreted by the fill rule; these fill a region if the path border encircles it an odd or non-zero number of times, respectively.

Not all graphics devices support this function: for example xfig and pictex do not.

Value

A grob object.

Author(s)

Paul Murrell

See Also

Grid, viewport

Examples

pathSample <- function(x, y, rule, gp = gpar()) {
    if (is.na(rule))
        grid.path(x, y, id = rep(1:2, each = 4), gp = gp)
    else
        grid.path(x, y, id = rep(1:2, each = 4), rule = rule, gp = gp)
    if (!is.na(rule))
        grid.text(paste("Rule:", rule), y = 0, just = "bottom")
}

pathTriplet <- function(x, y, title) {
    pushViewport(viewport(height = 0.9, layout = grid.layout(1, 3),
                          gp = gpar(cex = .7)))
    grid.rect(y = 1, height = unit(1, "char"), just = "top",
              gp = gpar(col = NA, fill = "grey"))
    grid.text(title, y = 1, just = "top")
    pushViewport(viewport(layout.pos.col = 1))
    pathSample(x, y, rule = "winding",
               gp = gpar(fill = "grey"))
    popViewport()
    pushViewport(viewport(layout.pos.col = 2))
    pathSample(x, y, rule = "evenodd",
               gp = gpar(fill = "grey"))
    popViewport()
    pushViewport(viewport(layout.pos.col = 3))
    pathSample(x, y, rule = NA)
    popViewport()
    popViewport()
}

pathTest <- function() {
    grid.newpage()
    pushViewport(viewport(layout = grid.layout(5, 1)))
    pushViewport(viewport(layout.pos.row = 1))
    pathTriplet(c(.1, .1, .9, .9, .2, .2, .8, .8),
                c(.1, .9, .9, .1, .2, .8, .8, .2),
                "Nested rectangles, both clockwise")
    popViewport()
    pushViewport(viewport(layout.pos.row = 2))
    pathTriplet(c(.1, .1, .9, .9, .2, .8, .8, .2),
                c(.1, .9, .9, .1, .2, .2, .8, .8),
                "Nested rectangles, outer clockwise, inner anti-clockwise")
    popViewport()
    pushViewport(viewport(layout.pos.row = 3))
    pathTriplet(c(.1, .1, .4, .4, .6, .9, .9, .6),
                c(.1, .4, .4, .1, .6, .6, .9, .9),
                "Disjoint rectangles")
    popViewport()
    pushViewport(viewport(layout.pos.row = 4))
    pathTriplet(c(.1, .1, .6, .6, .4, .4, .9, .9),
                c(.1, .6, .6, .1, .4, .9, .9, .4),
                "Overlapping rectangles, both clockwise")
    popViewport()
    pushViewport(viewport(layout.pos.row = 5))
    pathTriplet(c(.1, .1, .6, .6, .4, .9, .9, .4),
                c(.1, .6, .6, .1, .4, .4, .9, .9),
                "Overlapping rectangles, one clockwise, other anti-clockwise")
    popViewport()
    popViewport()
}

pathTest()

# Drawing multiple paths at once
holed_rect <- cbind(c(.15, .15, -.15, -.15, .1, .1, -.1, -.1), 
                    c(.15, -.15, -.15, .15, .1, -.1, -.1, .1))
holed_rects <- rbind(
    holed_rect + matrix(c(.7, .2), nrow = 8, ncol = 2, byrow = TRUE),
    holed_rect + matrix(c(.7, .8), nrow = 8, ncol = 2, byrow = TRUE),
    holed_rect + matrix(c(.2, .5), nrow = 8, ncol = 2, byrow = TRUE)
)
grid.newpage()
grid.path(x = holed_rects[, 1], y = holed_rects[, 2], 
          id = rep(1:6, each = 4), pathId = rep(1:3, each = 8),
          gp = gpar(fill = c('red', 'blue', 'green')),
          rule = 'evenodd')

# Not specifying pathId will treat all points as part of the same path, thus 
# having same fill
grid.newpage()
grid.path(x = holed_rects[, 1], y = holed_rects[, 2], 
          id = rep(1:6, each = 4),
          gp = gpar(fill = c('red', 'blue', 'green')),
          rule = 'evenodd')