1% File src/library/graphics/man/xspline.Rd 2% Part of the R package, https://www.R-project.org 3% Copyright 1995-2014 R Core Team 4% Distributed under GPL 2 or later 5 6\name{xspline} 7\alias{xspline} 8\title{Draw an X-spline} 9\description{ 10 Draw an X-spline, a curve drawn relative to control points. 11} 12\usage{ 13xspline(x, y = NULL, shape = 0, open = TRUE, repEnds = TRUE, 14 draw = TRUE, border = par("fg"), col = NA, \dots) 15} 16\arguments{ 17 \item{x,y}{vectors containing the coordinates of the vertices 18 of the polygon. See \code{\link{xy.coords}} for alternatives.} 19 \item{shape}{A numeric vector of values between -1 and 1, which 20 control the shape of the spline relative to the control points.} 21 \item{open}{A logical value indicating whether the spline is 22 an open or a closed shape.} 23 \item{repEnds}{For open X-splines, a logical value indicating whether 24 the first and last control points should be replicated for drawing 25 the curve. Ignored for closed X-splines.} 26 \item{draw}{logical: should the X-spline be drawn? If false, a set of 27 line segments to draw the curve is returned, and nothing is drawn.} 28 \item{border}{the color to draw the curve. Use \code{border = NA} to 29 omit borders.} 30 \item{col}{the color for filling the shape. The default, 31 \code{NA}, is to leave unfilled.} 32 \item{\dots}{\link{graphical parameters} such as \code{lty}, \code{xpd}, 33 \code{lend}, \code{ljoin} and \code{lmitre} can be given as arguments.} 34} 35\details{ 36 An X-spline is a line drawn relative to control points. For each 37 control point, the line may pass through (interpolate) the control 38 point or it may only approach (approximate) the control point; the 39 behaviour is determined by a shape parameter for each control point. 40 41 If the shape parameter is greater than zero, the spline approximates 42 the control points (and is very similar to a cubic B-spline when the 43 shape is 1). If the shape parameter is less than zero, the spline 44 interpolates the control points (and is very similar to a Catmull-Rom 45 spline when the shape is -1). If the shape parameter is 0, the spline 46 forms a sharp corner at that control point. 47 48 For open X-splines, the start and end control points must have a shape 49 of 0 (and non-zero values are silently converted to zero). 50 51 For open X-splines, by default the start and end control points are 52 replicated before the curve is drawn. A curve is drawn between 53 (interpolating or approximating) the second and third of each set of 54 four control points, so this default behaviour ensures that the 55 resulting curve starts at the first control point you have specified 56 and ends at the last control point. The default behaviour can be 57 turned off via the \code{repEnds} argument. 58} 59\value{ 60 If \code{draw = TRUE}, \code{NULL} otherwise a list with elements 61 \code{x} and \code{y} which could be passed to \code{\link{lines}}, 62 \code{\link{polygon}} and so on. 63 64 Invisible in both cases. 65} 66\note{ 67 Two-dimensional splines need to be created in an isotropic coordinate 68 system. Device coordinates are used (with an anisotropy correction if 69 needed.) 70} 71\references{ 72 Blanc, C. and Schlick, C. (1995), 73 \emph{X-splines : A Spline Model Designed for the End User}, 74 in \emph{Proceedings of SIGGRAPH 95}, pp.\sspace{}377--386. 75 \url{https://dept-info.labri.fr/~schlick/DOC/sig1.html} 76} 77\seealso{ 78 \code{\link{polygon}}. 79 80 \code{\link{par}} for how to specify colors. 81} 82\examples{ 83## based on examples in ?grid.xspline 84 85xsplineTest <- function(s, open = TRUE, 86 x = c(1,1,3,3)/4, 87 y = c(1,3,3,1)/4, ...) { 88 plot(c(0,1), c(0,1), type = "n", axes = FALSE, xlab = "", ylab = "") 89 points(x, y, pch = 19) 90 xspline(x, y, s, open, ...) 91 text(x+0.05*c(-1,-1,1,1), y+0.05*c(-1,1,1,-1), s) 92} 93op <- par(mfrow = c(3,3), mar = rep(0,4), oma = c(0,0,2,0)) 94xsplineTest(c(0, -1, -1, 0)) 95xsplineTest(c(0, -1, 0, 0)) 96xsplineTest(c(0, -1, 1, 0)) 97xsplineTest(c(0, 0, -1, 0)) 98xsplineTest(c(0, 0, 0, 0)) 99xsplineTest(c(0, 0, 1, 0)) 100xsplineTest(c(0, 1, -1, 0)) 101xsplineTest(c(0, 1, 0, 0)) 102xsplineTest(c(0, 1, 1, 0)) 103title("Open X-splines", outer = TRUE) 104 105par(mfrow = c(3,3), mar = rep(0,4), oma = c(0,0,2,0)) 106xsplineTest(c(0, -1, -1, 0), FALSE, col = "grey80") 107xsplineTest(c(0, -1, 0, 0), FALSE, col = "grey80") 108xsplineTest(c(0, -1, 1, 0), FALSE, col = "grey80") 109xsplineTest(c(0, 0, -1, 0), FALSE, col = "grey80") 110xsplineTest(c(0, 0, 0, 0), FALSE, col = "grey80") 111xsplineTest(c(0, 0, 1, 0), FALSE, col = "grey80") 112xsplineTest(c(0, 1, -1, 0), FALSE, col = "grey80") 113xsplineTest(c(0, 1, 0, 0), FALSE, col = "grey80") 114xsplineTest(c(0, 1, 1, 0), FALSE, col = "grey80") 115title("Closed X-splines", outer = TRUE) 116 117par(op) 118 119x <- sort(stats::rnorm(5)) 120y <- sort(stats::rnorm(5)) 121plot(x, y, pch = 19) 122res <- xspline(x, y, 1, draw = FALSE) 123lines(res) 124## the end points may be very close together, 125## so use last few for direction 126nr <- length(res$x) 127arrows(res$x[1], res$y[1], res$x[4], res$y[4], code = 1, length = 0.1) 128arrows(res$x[nr-3], res$y[nr-3], res$x[nr], res$y[nr], code = 2, length = 0.1) 129} 130\keyword{aplot} 131