Issue with guide_custom() messing up alignment of other guides

[kylebutts]

I'm not sure if this is a bug with ggplot2 or with gridtext, but I want to add a guide_custom with a custom grob via gridtext. This messes up the alignment of the color guide. This doesn't happen with grid::textGrob. gridtext::textbox_grob returns a gTree, so maybe that's causing the problem. If this is an issue with gridtext, feel free to close!

Reprex:

library(ggplot2)
library(gridtext)
library(palmerpenguins)
data(penguins) 

ggplot(
  penguins, aes(x = body_mass_g, y = flipper_length_mm, color = species)
) + 
  geom_point() +
  guides(
    custom = guide_custom(
      grob = grid::textGrob("Flipper Length (mm)", just = "right")
    )
  ) +
  theme(
    legend.box = "vertical",
    legend.location = "plot",
    legend.position = "top",
    legend.justification = c(0, 1),
  ) 
#> Warning: Removed 2 rows containing missing values or values outside the scale range
#> (`geom_point()`).

ggplot(
  penguins, aes(x = body_mass_g, y = flipper_length_mm, color = species)
) + 
  geom_point() +
  guides(
    custom = guide_custom(
      grob = gridtext::textbox_grob(
        "Flipper Length (mm)", hjust = 0
      )
    )
  ) +
  theme(
    legend.box = "vertical",
    legend.location = "plot",
    legend.position = "top",
    legend.justification = c(0, 1),
  ) 
#> Warning: Removed 2 rows containing missing values or values outside the scale range
#> (`geom_point()`).

^{Created on 2024-02-28 with reprex v2.1.0}

[teunbrand]

I think textbox grobs from {ggtext} don't self-report the width of the text, making placement somewhat more annoying.
You can use legend.box.just = "left" to make it work anyhow. Below I added a border to the legend background so you can see the alignment better.

library(ggplot2)
library(palmerpenguins)

ggplot(
  penguins, aes(x = body_mass_g, y = flipper_length_mm, color = species)
) + 
  geom_point() +
  guides(
    custom = guide_custom(
      grob = gridtext::textbox_grob(
        "Flipper Length (mm)", hjust = 0
      )
    )
  ) +
  theme(
    legend.box = "vertical",
    legend.box.just = "left",
    legend.location = "plot",
    legend.position = "top",
    legend.justification = c(0, 1),
    legend.background = element_rect(colour = "black")
  ) 
#> Warning: Removed 2 rows containing missing values or values outside the scale range
#> (`geom_point()`).

^{Created on 2024-02-28 with reprex v2.1.0}

[clauswilke]

If it's a feature that is missing in gridtext please file an issue there. A PR with a fix would be even better.

https://github.com/wilkelab/gridtext/issues

[teunbrand]

Now I'm starting to doubt guide_custom() again as it seems to have the wrong box for the regular text grob.
I'll try to dig a bit deeper in the coming days.

library(ggplot2)
library(palmerpenguins)

ggplot(
  penguins, aes(x = body_mass_g, y = flipper_length_mm, color = species)
) + 
  geom_point() +
  guides(
    custom = guide_custom(
      grob = grid::textGrob("Flipper Length (mm)", just = "right")
    )
  ) +
  theme(
    legend.box = "vertical",
    legend.location = "plot",
    legend.position = "top",
    legend.justification = c(0, 1),
    legend.background = element_rect(colour = "black")
  ) 
#> Warning: Removed 2 rows containing missing values or values outside the scale range
#> (`geom_point()`).

^{Created on 2024-02-28 with reprex v2.1.0}

[teunbrand]

I've done a bit of investigating and this is going on.

For the textGrob() thing: the text is right-aligned to the center point of the area. So when using just = "right", you should simultaneously set x = unit(1, "npc") to properly right-align it. This is precisely the 'point-based' versus 'width/height-based' thing the internal titleGrob() function resolves for ggplot2.

For the textbox_grob() thing: it is doing the correct thing, except the default width = unit(1, "npc") should be set to NULL to use the actual width of the text. I can imagine the default is useful in some cases, so nothing is wrong with {gridtext}.

The legend.box.just setting is useful to set in this case anyway. So while yes, there are some confusing elements with guide_custom(), these mostly relate to grid-level details over which ggplot2 has little control. As everything appears to be in working order, I'm going to consider this issue resolved.

[kylebutts]

Thank you @teunbrand! This is all super helpful!