Pass fill value to legend key icons

[808sAndBR]

Resolves: #3455

Below is reprex of this working:

# sample data
dat <- data.frame(
  x = as.factor(1:10),
  y = c(20,30,13,37,12,50,31,2,40,30),
  z = rep('a', 10)
)

# basic plot
ggplot(dat) +
  geom_segment(
    aes(x = x, xend = x, y = 0, yend = y+15, linetype = z), 
    arrow = arrow(length = unit(0.25, 'cm'), type = 'closed'),
    size = 0.7
  ) 

New output:

Old output:

[thomasp85]

Looks good! Thanks

[clauswilke]

I have two concerns about this:

1. geom_segment() has a parameter arrow.fill. We should see if we can carry it through to the legend and use if defined.

2. I'm wondering whether this draw key is used by any geoms that meaningfully use a fill aesthetic, and whether in this case filling the arrow in the way it is done now will create strange results. Possibly we need a new draw key specifically for geom_segment().

[thomasp85]

I don't think we can do this for geom_segment specifically. Any segment and path type geom can have arrowheads and they should behave as expected.

Your concern about the arrow.fill argument is valid though... is there a straightforward way to pass this through?

[808sAndBR]

I believe that this new version passes the arrow.fill through as expected, but let me know if it looks questionable.

For the second concern. I ran this version of legend_draw on everywhere that I saw importing it:

geom_sf
geom_errorbar
geom_path
geom_segment
geom_rug
geom_hline

None of the outputs seems strange to me, but I have them in a Rmd if you want to swing by and see if you notice anything strange.

[clauswilke]

Yes, ignore my 2nd concern, it doesn't apply.

However, for my 1st concern, a little more needs to be done. First, arrow.fill should be the first choice for fill, not the second, as it is the case in the geom. See here:

ggplot2/R/geom-segment.r

Line 116 in 7e6d125

arrow.fill <- arrow.fill %||% coord$colour

and here:

ggplot2/R/geom-segment.r

Line 121 in 7e6d125

fill = alpha(arrow.fill, coord$alpha),

Second, I doubt data$arrow.fill will work. I think it has to be params$arrow.fill. In either case, I think it's important that you run a test to check whether this actually works.

Finally, I wouldn't discount the fill variable, so the final sequence should read:
params$arrow.fill %||% data$colour %||% data$fill %||% "black"

[808sAndBR]

Thanks for all the extra info, it's been super helpful for understanding how this all works behind the scenes.

Ahhhh, I see I think it picking up "black" from the back of the options which made me think it was working as expected.

I have added some more robust test cases (below) to make sure this is working as expected. I think it looks right to me, but let me know if anything seems off.

# sample data
dat <- data.frame(
  x = as.factor(1:10),
  y = c(20,30,13,37,12,50,31,2,40,30),
  z = rep('a', 10)
)

# basic plot
ggplot(dat) +
  geom_segment(
    aes(x = x, xend = x, y = 0, yend = y+15, linetype = z), 
    arrow = arrow(length = unit(0.25, 'cm'), type = 'closed'),
    size = 0.7
  ) 

ggplot(dat) +
  geom_segment(
    aes(x = x, xend = x, y = 0, yend = y+15, linetype = z), 
    arrow = arrow(length = unit(0.25, 'cm'), type = 'closed'),
    arrow.fill = 'red',
    size = 0.7
  ) 

ggplot(dat) +
  geom_segment(
    aes(x = x, xend = x, y = 0, yend = y+15, linetype = z, colour='yellow'), 
    arrow = arrow(length = unit(0.25, 'cm'), type = 'closed'),
    size = 0.7
  ) 

ggplot(dat) +
  geom_segment(
    aes(x = x, xend = x, y = 0, yend = y+15, linetype = z, colour='yellow'), 
    arrow = arrow(length = unit(0.25, 'cm'), type = 'closed'),
    arrow.fill = 'blue',
    size = 0.7
  ) 

[clauswilke]

Looks great, thanks!

Going forward, I suggest you check out the reprex package, so you don't have to copy and paste screenshots.