vwline (version 0.2-2)

edgePoints: Calculate edge points

Description

Calculate points on the edge or boundary of a variable-width line.

Usage

edgePoints(x, d, ...)
# S3 method for vwcurveGrob
edgePoints(x, d, which = c("left", "right"), direction = "forward", debug = FALSE, ...) 
# S3 method for vwlineGrob
edgePoints(x, d, x0, y0, which = 1, direction = "forward", debug = FALSE, ...) 
# S3 method for vwXsplineGrob
edgePoints(x, d, which = c("left", "right"), direction = "forward", debug = FALSE, ...)
# S3 method for brushXsplineGrob
edgePoints(x, d, x0, y0, which = 1, direction = "forward", debug = FALSE, ...) 
# S3 method for offsetXsplineGrob
edgePoints(x, d, x0, y0, which = 1, direction = "forward", debug = FALSE, ...)

Value

For methods with a single boundary, a list with components x and y, giving locations on the edge of the variable-width line, and tangent, giving the tangent to the edge at each location.

For methods with distinct left and right edges, a list with components

left and right, each a list as above.

Arguments

x

A variable-width line grob.

d

A numeric vector or unit specifying locations along the boundary of the variable-width line.

which

For some methods, this is either "left" or "right" (or both) indicating which edge to find locations on. For other methods, this is a numeric, selecting which boundary to find locations on. See Details.

direction

Either "forwards" or "backwards" to indicate the direction of traversal for the edge.

x0, y0

A location used to determine the start point for traversing an edge.

debug

A logical indicating whether to draw graphical debugging information.

...

Additional arguments for methods.

Author

Paul Murrell

Details

If the distance is numeric, it is assumed to be a proportion of the length of an edge.

What constitutes an edge varies between different methods: some methods produce distinct left and right edges (ignoring line endings), in which case locations can be found on either edge; other methods generally produce a single boundary (including line endings), but self-intersecting lines can produce additional boundaries.

For some methods, it is possible for a boundary to form loops, so an edge location is not guaranteed to be on the external boundary of the variable-width line.

For lines with distinct left and right edges, the forwards direction is the direction of the main curve. For lines with a single boundary, the forwards direction is anticlockwise.

For lines with a single boundary, the start point on the boundary is defined as the nearest point on the boundary to the location specified by x0 and y0.

See Also

grid.vwcurve, grid.vwline, grid.vwXspline, grid.brushXspline, grid.offsetXspline

Examples

grid.newpage()
x <- seq(.2, .8, length.out=100)
y <- .05*sin(seq(0, 2*pi, length.out=100))
w <- unit(seq(2, 10, length.out=100), "mm")
vwcg <- vwcurveGrob(x, y + 2/3, w, lineend="round",
                    gp=gpar(col="black"))
grid.draw(vwcg)
epts <- edgePoints(vwcg, 0:9/9)
grid.circle(epts$left$x, epts$left$y, r=unit(1, "mm"), 
            gp=gpar(fill=hcl(0, 80, seq(10, 100, 10))))
x <- c(.2, .4, .6, .8)
y <- c(-.05, .05, -.05, .05)
w <- unit(c(2, 4, 6, 8), "mm")
vwbg <- brushXsplineGrob(circleBrush(), x, y + 1/3, w,
                         gp=gpar(col="black"))
grid.draw(vwbg)
epts <- edgePoints(vwbg, unit(0:9, "cm"), x0=0, y0=1/3)
grid.circle(epts$x, epts$y, r=unit(1, "mm"), 
            gp=gpar(fill=hcl(0, 80, seq(10, 100, 10))))