尽管线宽如何保持线型间距不变

How to keep linetype spacing constant despite line size

我一直在尝试在 ggplot2 或网格中绘制线条,当尺寸不同时,线段之间的间距相等。但是我一直没有成功所以我请求你的帮助。

在下面的示例中,如何在线宽不同的情况下保持线段之间的绝对间距相等?

我想避免自己制作自定义 makeContent.myclass 方法来控制它。

library(ggplot2)
library(grid)

df <- data.frame(
  x = c(1:2, 1:2),
  y = c(1:2, 2:1),
  size = c(1,1,10,10)
)

# In ggplot2
ggplot(df, aes(x, y, size = size, group = size)) +
  geom_line(linetype = 2)

# In grid
lines <- polylineGrob(
  x = scales::rescale(df$x), 
  y = scales::rescale(df$y), 
  id = c(1,1,2,2),
  gp = gpar(lty = 2, lwd = c(1, 10))
)

grid.newpage(); grid.draw(lines)

我想要类似于以下插图画家制作的东西。注意红线段是等长的。

有什么想法吗?感谢阅读!

这可能不是您要找的 Teunbrand,但我想您可以将您的线条转换为一系列沿线条等距分布的细多边形。

此函数采用一系列 x 和 y 坐标和 returns 虚线(作为单个 treeGrob)。根据你的例子,它 returns 它在标准化的 npc 坐标中。您可以完全控制线宽、破折号长度和中断长度(但不是图案)以及颜色。恐怕单位有点随意,这与生产标准相去甚远,但它相当有效:

segmentify <- function(x, y, linewidth = 1, dash_len = 1, 
                       break_len = 1, col = "black")
{
  
  linewidth <- 0.002 * linewidth
  dash_len  <- 0.01  * dash_len
  break_len <- 0.04  * break_len

  if(length(y) != length(x)) 
    stop("x and y must be the same length")
  if(!is.numeric(x) | !is.numeric(y))
    stop("x and y must be numeric vectors")
  if(length(x) < 2)
    stop("Insufficient x, y pairs to make line.")
  
  x <- scales::rescale(x)
  y <- scales::rescale(y)
  
  n_dashes <- 0
  skip_len <- break_len + dash_len
  
   df <- list()
  for(i in seq_along(x)[-1])
  {
    x_diff          <- x[i] - x[i - 1]
    y_diff          <- y[i] - y[i - 1]
    seg_len         <- sqrt(x_diff^2 + y_diff^2)
    seg_prop        <- skip_len / seg_len
    dist_from_start <- n_dashes * skip_len
    prop_start      <- dist_from_start/seg_len
    x_start         <- x[i-1] + prop_start * x_diff
    y_len           <- y_diff * seg_prop
    x_len           <- x_diff * seg_prop
    y_start         <- y[i-1] + prop_start * y_diff
    n_breaks        <- (seg_len - dist_from_start)/skip_len
    n_dashes        <- (n_dashes + n_breaks) %% 1
    n_breaks        <- floor(n_breaks)
    
    if(n_breaks)
    {
       df[[length( df) + 1]] <- data.frame(
        x = seq(x_start, x[i], by = x_len),
        y = seq(y_start, y[i], by = y_len)
        )
       df[[length( df)]]$theta <-
        atan(rep(y_diff/x_diff, length( df[[length( df)]]$x)))
    }
  }
  
   df <- do.call(rbind,  df)
   df$x1 <-  df$x + sin( df$theta) * linewidth + cos(df$theta) * dash_len
   df$x2 <-  df$x + sin( df$theta) * linewidth - cos(df$theta) * dash_len
   df$x3 <-  df$x - sin( df$theta) * linewidth - cos(df$theta) * dash_len
   df$x4 <-  df$x - sin( df$theta) * linewidth + cos(df$theta) * dash_len
   
   df$y1 <-  df$y - cos( df$theta) * linewidth + sin(df$theta) * dash_len
   df$y2 <-  df$y - cos( df$theta) * linewidth - sin(df$theta) * dash_len
   df$y3 <-  df$y + cos( df$theta) * linewidth - sin(df$theta) * dash_len
   df$y4 <-  df$y + cos( df$theta) * linewidth + sin(df$theta) * dash_len
  
   do.call(grid::grobTree, lapply(seq(nrow(df)), function(i) {
    grid::polygonGrob(c(df$x1[i], df$x2[i], df$x3[i], df$x4[i]), 
                      c(df$y1[i], df$y2[i], df$y3[i], df$y4[i]),
              gp = gpar(col = "#00000000", lwd = 0, fill = col))
   }))

}

使用起来相当简单:

set.seed(2)

x <- 1:10
y <- rnorm(10)

grid::grid.newpage()
grid::grid.draw(segmentify(x, y))

而在不影响间距的情况下改变线宽是这样的:

grid::grid.newpage()
grid::grid.draw(segmentify(x, y, linewidth = 3))

您可以像这样控制间距和颜色:

grid::grid.newpage()
grid::grid.draw(segmentify(x, y, linewidth = 2, break_len = 0.5, col = "forestgreen"))

好吧,在 Allan 的鼓励下,我自己画了一些东西并没有那么糟糕,我决定也尝试解决这个问题。它正在做我试图避免这个问题的事情,但它可能对你们其他人有帮助。

我采用了稍微不同的方法,主要区别在于 (1) 我们保留多段线而不是转换为多边形,以及 (2) 我不太熟悉三角函数,所以我使用 approxfun() 代替插入线和 (3) 我们将使用绝对单位而不是相对单位,因此在调整设备大小时不会很尴尬。

首先,因为我打算在自定义 geom 函数中使用它,所以我的目标是制作一个易于粘贴到 geom 绘制方法末尾的 grob 结构。你可以给它一个 grob,或者一个 grob 的参数。它更改了 grob 的 class,稍后将变得相关,删除了线型参数并添加了破折号和断线的信息。

library(grid)
library(scales)

linetypeGrob <- function(x, ..., dashes = 1, breaks = 1) {
  if (!inherits(x, "polyline")) {
    x <- polylineGrob(x, ...)
  }
  class(x)[[1]] <- "linetypeGrob"
  x$gp$lty <- NULL
  x$dashes <- dashes
  x$breaks <- breaks
  x
}

现在正如我上面提到的,我们将回到 class。自定义 grob classes 的巧妙之处在于,您可以在绘制它们之前拦截它们,以便您可以进行最后一刻的更改。为此,我们对grid中的makeContext函数写了一个S3方法,进行相应的修改。我知道这是一个很长的函数,但我试图通过插入说明我正在尝试做什么的注释来使其更容易理解。

makeContext.linetypeGrob <- function(x) {
  # Sort out line IDs
  id <- x$id
  if (is.null(id)) {
    if (is.null(x$id.lengths)) {
      id <- rep(1L, length(x$x))
    } else {
      id <- rep(seq_along(x$id.lengths), x$id.lengths)
    }
  }

  # Delete previous line IDs
  x$id <- NULL
  x$id.lengths <- NULL

  # Take dashes and breaks parameters out of the old grob
  dashes <- x$dashes
  x$dashes <- NULL
  breaks <- x$breaks
  x$breaks <- NULL

  # Convert to absolute units
  newx <- convertX(x$x, "mm", TRUE)
  newy <- convertY(x$y, "mm", TRUE)

  # Express lines as points along a cumulative distances
  dist <- sqrt(diff(newx)^2 + diff(newy)^2)
  cumdist <- cumsum(c(0, dist))

  # Take new lines as a sequence along the cumulative distance
  starts <- seq(0, max(cumdist), by = (dashes + breaks))
  ends <- seq(dashes, max(cumdist), by = (dashes + breaks))
  if (length(ends) == length(starts) - 1) {
    # Case when the end actually should have gone beyond `max(cumdist)`
    ends <- c(ends, max(cumdist))
  }

  # Set index for graphical parameters
  gp_i <- findInterval(starts, cumdist[cumsum(rle(id)$lengths)]) + 1

  # Basically dealing with elbow pieces a bit
  # Find mismatches between the original segments that starts and ends fall on
  start_id <- findInterval(starts, cumdist)
  end_id <- findInterval(ends, cumdist)
  mismatch <- which(start_id != end_id)

  # Insert elbow pieces
  starts <- c(starts, cumdist[end_id[mismatch]])
  starts <- starts[{o <- order(starts)}] # Need the order for later
  ends <- sort(c(ends, cumdist[end_id[mismatch]]))

  # Join elbow pieces
  new_id <- seq_along(start_id)
  if (length(mismatch)) {
    i <- rep_len(1, length(new_id))
    i[mismatch] <- 2
    new_id <- rep(new_id, i)
  }

  # Seperate lines with different IDs
  keepfun <- approxfun(cumdist, id)
  keep <- (keepfun(starts) %% 1) == 0 & (keepfun(ends) %% 1) == 0

  # Interpolate x
  xfun <- approxfun(cumdist, newx)
  x0 <- xfun(starts[keep])
  x1 <- xfun(ends[keep])

  # Interpolate y
  yfun <- approxfun(cumdist, newy)
  y0 <- yfun(starts[keep])
  y1 <- yfun(ends[keep])

  # Expand graphic parameters by new ID
  x$gp[] <- lapply(x$gp, function(x){
    if (length(x) == 1) {
      return(x)
    } else {
      x[as.integer(gp_i)]
    }
  })

  # Put everything back into the grob
  x$x <- unit(as.vector(rbind(x0, x1)), "mm")
  x$y <- unit(as.vector(rbind(y0, y1)), "mm")
  x$id <- as.vector(rbind(new_id[keep], new_id[keep]))
  class(x)[[1]] <- "polyline"
  x
}

最后,为了证明它的工作原理,我将使用这个新的 grob 绘制一些虚拟数据。您可以像绘制普通多段线 grob 一样使用它。

set.seed(100)
x <- c(cumsum(rnorm(10)), cumsum(rnorm(10)))
y <- c(cumsum(rnorm(10)), cumsum(rnorm(10)))
id <- rep(c(1, 2), each = 10)
gp <- gpar(lwd = c(2, 10), lineend = "butt",
           col = c("magenta", "blue"))


grob <- linetypeGrob(scales::rescale(x),
                     scales::rescale(y),
                     id = id, gp = gp, dashes = 5, breaks = 2)

grid.newpage(); grid.draw(grob)

您可以看到,如果我调整设备大小,破折号和折线的长度保持不变: