Ducj:

#' legend is overlay in plot
#'
#' @param non parameters.
#' @return overlab of plot
#' @examples
#' plot(1)
#' p_legend('x')
#' @export

p_legend<-function (legend, fill = NULL, col = par("col"),
          border = "black", lty, lwd, pch, angle = 45, density = NULL,
          bty = "o", bg = par("bg"), box.lwd = par("lwd"), box.lty = par("lty"),
          box.col = par("fg"), pt.bg = NA, cex = 1, pt.cex = cex,
          pt.lwd = lwd, xjust = 0, yjust = 1, x.intersp = 1, y.intersp = 1,
          adj = c(0, 0.5), text.width = NULL, text.col = par("col"),
          text.font = NULL, merge = do.lines && has.pch, trace = FALSE,
          plot = TRUE, ncol = 1, horiz = FALSE, title = NULL, inset = 0,
          xpd, title.col = text.col, title.adj = 0.5, seg.len = 2)
{l<-locator(1);x<-l$x;y<-l$y
if (missing(legend) && !missing(y) && (is.character(y) ||
                                       is.expression(y))) {
  legend <- y
  y <- NULL
}
mfill <- !missing(fill) || !missing(density)
if (!missing(xpd)) {
  op <- par("xpd")
  on.exit(par(xpd = op))
  par(xpd = xpd)
}
title <- as.graphicsAnnot(title)
if (length(title) > 1)
  stop("invalid 'title'")
legend <- as.graphicsAnnot(legend)
n.leg <- if (is.call(legend))
  1
else length(legend)
if (n.leg == 0)
  stop("'legend' is of length 0")
auto <- if (is.character(x))
  match.arg(x, c("bottomright", "bottom", "bottomleft",
                 "left", "topleft", "top", "topright", "right", "center"))
else NA
if (is.na(auto)) {
  xy <- xy.coords(x, y, setLab = FALSE)
  x <- xy$x
  y <- xy$y
  nx <- length(x)
  if (nx < 1 || nx > 2)
    stop("invalid coordinate lengths")
}
else nx <- 0
xlog <- par("xlog")
ylog <- par("ylog")
rect2 <- function(left, top, dx, dy, density = NULL, angle,
                  ...) {
  r <- left + dx
  if (xlog) {
    left <- 10^left
    r <- 10^r
  }
  b <- top - dy
  if (ylog) {
    top <- 10^top
    b <- 10^b
  }
  rect(left, top, r, b, angle = angle, density = density,
       ...)
}
segments2 <- function(x1, y1, dx, dy, ...) {
  x2 <- x1 + dx
  if (xlog) {
    x1 <- 10^x1
    x2 <- 10^x2
  }
  y2 <- y1 + dy
  if (ylog) {
    y1 <- 10^y1
    y2 <- 10^y2
  }
  segments(x1, y1, x2, y2, ...)
}
points2 <- function(x, y, ...) {
  if (xlog)
    x <- 10^x
  if (ylog)
    y <- 10^y
  points(x, y, ...)
}
text2 <- function(x, y, ...) {
  if (xlog)
    x <- 10^x
  if (ylog)
    y <- 10^y
  text(x, y, ...)
}
if (trace)
  catn <- function(...) do.call("cat", c(lapply(list(...),
                                                formatC), list("\n")))
cin <- par("cin")
Cex <- cex * par("cex")
if (is.null(text.width))
  text.width <- max(abs(strwidth(legend, units = "user",
                                 cex = cex, font = text.font)))
else if (!is.numeric(text.width) || text.width < 0)
  stop("'text.width' must be numeric, >= 0")
xc <- Cex * xinch(cin[1L], warn.log = FALSE)
yc <- Cex * yinch(cin[2L], warn.log = FALSE)
if (xc < 0)
  text.width <- -text.width
xchar <- xc
xextra <- 0
yextra <- yc * (y.intersp - 1)
ymax <- yc * max(1, strheight(legend, units = "user", cex = cex)/yc)
ychar <- yextra + ymax
if (trace)
  catn("  xchar=", xchar, "; (yextra,ychar)=", c(yextra,
                                                 ychar))
if (mfill) {
  xbox <- xc * 0.8
  ybox <- yc * 0.5
  dx.fill <- xbox
}
do.lines <- (!missing(lty) && (is.character(lty) || any(lty >
                                                          0))) || !missing(lwd)
n.legpercol <- if (horiz) {
  if (ncol != 1)
    warning(gettextf("horizontal specification overrides: Number of columns := %d",
                     n.leg), domain = NA)
  ncol <- n.leg
  1
}
else ceiling(n.leg/ncol)
has.pch <- !missing(pch) && length(pch) > 0
if (do.lines) {
  x.off <- if (merge)
    -0.7
  else 0
}
else if (merge)
  warning("'merge = TRUE' has no effect when no line segments are drawn")
if (has.pch) {
  if (is.character(pch) && !is.na(pch[1L]) && nchar(pch[1L],
                                                    type = "c") > 1) {
    if (length(pch) > 1)
      warning("not using pch[2..] since pch[1L] has multiple chars")
    np <- nchar(pch[1L], type = "c")
    pch <- substr(rep.int(pch[1L], np), 1L:np, 1L:np)
  }
  if (!is.character(pch))
    pch <- as.integer(pch)
}
if (is.na(auto)) {
  if (xlog)
    x <- log10(x)
  if (ylog)
    y <- log10(y)
}
if (nx == 2) {
  x <- sort(x)
  y <- sort(y)
  left <- x[1L]
  top <- y[2L]
  w <- diff(x)
  h <- diff(y)
  w0 <- w/ncol
  x <- mean(x)
  y <- mean(y)
  if (missing(xjust))
    xjust <- 0.5
  if (missing(yjust))
    yjust <- 0.5
}
else {
  h <- (n.legpercol + (!is.null(title))) * ychar + yc
  w0 <- text.width + (x.intersp + 1) * xchar
  if (mfill)
    w0 <- w0 + dx.fill
  if (do.lines)
    w0 <- w0 + (seg.len + x.off) * xchar
  w <- ncol * w0 + 0.5 * xchar
  if (!is.null(title) && (abs(tw <- strwidth(title, units = "user",
                                             cex = cex) + 0.5 * xchar)) > abs(w)) {
    xextra <- (tw - w)/2
    w <- tw
  }
  if (is.na(auto)) {
    left <- x - xjust * w
    top <- y + (1 - yjust) * h
  }
  else {
    usr <- par("usr")
    inset <- rep_len(inset, 2)
    insetx <- inset[1L] * (usr[2L] - usr[1L])
    left <- switch(auto, bottomright = , topright = ,
                   right = usr[2L] - w - insetx, bottomleft = ,
                   left = , topleft = usr[1L] + insetx, bottom = ,
                   top = , center = (usr[1L] + usr[2L] - w)/2)
    insety <- inset[2L] * (usr[4L] - usr[3L])
    top <- switch(auto, bottomright = , bottom = , bottomleft = usr[3L] +
                    h + insety, topleft = , top = , topright = usr[4L] -
                    insety, left = , right = , center = (usr[3L] +
                                                           usr[4L] + h)/2)
  }
}
if (plot && bty != "n") {
  if (trace)
    catn("  rect2(", left, ",", top, ", w=", w, ", h=",
         h, ", ...)", sep = "")
  rect2(left, top, dx = w, dy = h, col = bg, density = NULL,
        lwd = box.lwd, lty = box.lty, border = box.col)
}
xt <- left + xchar + xextra + (w0 * rep.int(0:(ncol - 1),
                                            rep.int(n.legpercol, ncol)))[1L:n.leg]
yt <- top - 0.5 * yextra - ymax - (rep.int(1L:n.legpercol,
                                           ncol)[1L:n.leg] - 1 + (!is.null(title))) * ychar
if (mfill) {
  if (plot) {
    if (!is.null(fill))
      fill <- rep_len(fill, n.leg)
    rect2(left = xt, top = yt + ybox/2, dx = xbox, dy = ybox,
          col = fill, density = density, angle = angle,
          border = border)
  }
  xt <- xt + dx.fill
}
if (plot && (has.pch || do.lines))
  col <- rep_len(col, n.leg)
if (missing(lwd) || is.null(lwd))
  lwd <- par("lwd")
if (do.lines) {
  if (missing(lty) || is.null(lty))
    lty <- 1
  lty <- rep_len(lty, n.leg)
  lwd <- rep_len(lwd, n.leg)
  ok.l <- !is.na(lty) & (is.character(lty) | lty > 0) &
    !is.na(lwd)
  if (trace)
    catn("  segments2(", xt[ok.l] + x.off * xchar, ",",
         yt[ok.l], ", dx=", seg.len * xchar, ", dy=0, ...)")
  if (plot)
    segments2(xt[ok.l] + x.off * xchar, yt[ok.l], dx = seg.len *
                xchar, dy = 0, lty = lty[ok.l], lwd = lwd[ok.l],
              col = col[ok.l])
  xt <- xt + (seg.len + x.off) * xchar
}
if (has.pch) {
  pch <- rep_len(pch, n.leg)
  pt.bg <- rep_len(pt.bg, n.leg)
  pt.cex <- rep_len(pt.cex, n.leg)
  pt.lwd <- rep_len(pt.lwd, n.leg)
  ok <- !is.na(pch)
  if (!is.character(pch)) {
    ok <- ok & (pch >= 0 | pch <= -32)
  }
  else {
    ok <- ok & nzchar(pch)
  }
  x1 <- (if (merge && do.lines)
    xt - (seg.len/2) * xchar
    else xt)[ok]
  y1 <- yt[ok]
  if (trace)
    catn("  points2(", x1, ",", y1, ", pch=", pch[ok],
         ", ...)")
  if (plot)
    points2(x1, y1, pch = pch[ok], col = col[ok], cex = pt.cex[ok],
            bg = pt.bg[ok], lwd = pt.lwd[ok])
}
xt <- xt + x.intersp * xchar
if (plot) {
  if (!is.null(title))
    text2(left + w * title.adj, top - ymax, labels = title,
          adj = c(title.adj, 0), cex = cex, col = title.col)
  text2(xt, yt, labels = legend, adj = adj, cex = cex,
        col = text.col, font = text.font)
}
invisible(list(rect = list(w = w, h = h, left = left, top = top),
               text = list(x = xt, y = yt)))
}
#plot(1)

#devtools::document()