为什么geom_segment创建具有透明度的笔画？

Question

下面有我的代码的简化版本。该段显示为半透明，如第二段覆盖的第一段所突出显示的那样，该段显示具有更多alpha的白色。

如果打开在Adobe Illustrator中另存为SVG的图像，则透明度设置为50％，这说明了为什么看起来像它，但是我不知道为什么当我未设置时将其设置为50％它（但将alpha设置为1）。

library(tidyverse)
g <- ggplot() +      
  theme_void() +
  theme(
    plot.background = element_rect(fill = "black"),
  ) +
  #coord_polar() +
  scale_color_identity() +
  #plot distance - facing outwards
  geom_segment(aes(x = 1, xend = 3,
                   y = 1, yend = 3,
                   colour = "white", alpha = 1),
               size = 1, inherit.aes = FALSE) +
  geom_segment(aes(x = 1, xend = 2,
                   y = 1, yend = 2,
                   colour = "white", alpha = 1),
               size = 1, inherit.aes = FALSE)

g

Answer 1

我想您只需要将colour和alpha从aes功能中移出即可。您编写它的方式是将它们作为要解释的变量而不是绝对值传递：

library(tidyverse)
g <- ggplot() +      
  theme_void() +
  theme(
    plot.background = element_rect(fill = "black"),
  ) +
  #coord_polar() +
  scale_color_identity() +
  #plot distance - facing outwards
  geom_segment(aes(x = 1, xend = 3,
                   y = 1, yend = 3),
                   colour = "white", alpha = 1,
               size = 1, inherit.aes = FALSE) +
  geom_segment(aes(x = 1, xend = 2,
                   y = 1, yend = 2),
                   colour = "white", alpha = 1,
               size = 1, inherit.aes = FALSE)

g