Closed arrow on `axis.line` is not filled

[martisak]

The arrow on axis.line is not filled when the type is set to "closed", however other arrows of the same type are filled. See example.

library(tidyverse)

arrow = arrow(angle=10, type = "closed")
ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, color=Species)) +
    geom_point() +
    theme(axis.line = element_line(arrow=arrow)) +
    annotate("segment", x = 3, xend = min(iris$Sepal.Length), y = 4, yend = 3, arrow=arrow)

^{Created on 2018-10-01 by the reprex package (v0.2.1)}

[ptoche]

See https://github.com/tidyverse/ggplot2/pull/2375 and https://stackoverflow.com/questions/47878787/fill-arrow-on-geom-curve-ggplot2. Looks like recent fixes to geom_curve and geom_segment do not apply to element_line. Passing arrow.fill or color to element_line() doesn't seem to do anything...

theme(axis.line = element_line(arrow=arrow(type = "closed"), arrow.fill = "black"))

[batpigandme]

Right, so the only adjustment to arrow specified is that it's closed:

library(tidyverse)

arrow = arrow(angle=10, type = "closed")
ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, color=Species)) +
  geom_point() +
  theme(axis.line = element_line(arrow=arrow)) +
  annotate("segment", x = 3, xend = min(iris$Sepal.Length), y = 4, yend = 3, arrow=arrow)

arrow = arrow(angle=10)
ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, color=Species)) +
  geom_point() +
  theme(axis.line = element_line(arrow=arrow)) +
  annotate("segment", x = 3, xend = min(iris$Sepal.Length), y = 4, yend = 3, arrow=arrow)

^{Created on 2018-10-01 by the reprex package (v0.2.1.9000)}

The arrow.fill argument only works currently for geom_segment() and geom_curve() NEWS here:

geom_segment() and geom_curve() have a new arrow.fill parameter which allows you to specify a separate fill colour for closed arrowheads (@hrbrmstr and @clauswilke, #2375).

[yutannihilation]

I roughly feel element_line() can have arrow.fill just as #2375 did. It can be passed to gpar() around here, and then it is passed to polylineGrob().

ggplot2/R/theme-elements.r

Line 229 in 7ed8930

gp <- gpar(lwd = len0_null(size * .pt), col = colour, lty = linetype, lineend = lineend)

[yutannihilation]

Here's a PoC: yutannihilation#2

But, adding a new parameter may break the existing theme; we get relatively little gain compared to the risk? Sorry, I think I'm not really sure how theme works...

[clauswilke]

As a workaround, you can turn clipping off in the coord and then just replace the axis line with a segment drawn by geom_segment() at the edge of the coordinate system.

[clauswilke]

@yutannihilation I'm not immediately sure about the implications of a new parameter either. But I would argue that a filled arrow should by default be filled with the color that is used to draw the outline. Maybe you could implement that, without adding a new parameter?

[clauswilke]

Then, if somebody really needs a different fill color, they can use the geom_segment() workaround I described in the previous comment.

[yutannihilation]

Agreed, thanks. I was thinking too complicatedly.

[lock]

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