geom_textsegment() with arrow() draws line to the top left of the plot

[erikvona]

As in the title, geom_textsegment() with arrow() draws a line starting from where the text starts to the top left of the plot.

Using the example from the docs:

ggplot(mapping = aes(x, y)) +
    geom_col(
        data = data.frame(x = c(1, 2), y = c(1, 10))
    ) +
    annotate(
        "textsegment",
        x = 1, xend = 2, y = 1, yend = 10,
        label = "10x increase", arrow = arrow()
    )

The output:

sessionInfo():

R version 4.1.2 (2021-11-01)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18363)

Matrix products: default

locale:
[1] LC_COLLATE=Dutch_Netherlands.1252  LC_CTYPE=Dutch_Netherlands.1252    LC_MONETARY=Dutch_Netherlands.1252 LC_NUMERIC=C                      
[5] LC_TIME=Dutch_Netherlands.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] geomtextpath_0.1.0 ggplot2_3.3.5     

loaded via a namespace (and not attached):
 [1] magrittr_2.0.1    tidyselect_1.1.1  munsell_0.5.0     colorspace_2.0-2  R6_2.5.1          rlang_0.4.12      fansi_0.5.0       dplyr_1.0.7      
 [9] tools_4.1.2       grid_4.1.2        gtable_0.3.0      utf8_1.2.2        DBI_1.1.2         withr_2.4.3       systemfonts_1.0.3 ellipsis_0.3.2   
[17] digest_0.6.29     assertthat_0.2.1  tibble_3.1.6      lifecycle_1.0.1   crayon_1.4.2      textshaping_0.3.6 farver_2.1.0      purrr_0.3.4      
[25] vctrs_0.3.8       glue_1.6.0        labeling_0.4.2    compiler_4.1.2    pillar_1.6.4      generics_0.1.1    scales_1.1.1      pkgconfig_2.0.3  

This happens regardless if I use geom_textsegment as an annotation.

[teunbrand]

Hi there, thanks for letting us know!

I can reproduce this on the default windows device, but not using the {ragg} graphics device. Reprex with default windows device:

library(geomtextpath)
#> Warning: package 'geomtextpath' was built under R version 4.1.2
#> Loading required package: ggplot2

ggplot(mapping = aes(x, y)) +
  geom_col(
    data = data.frame(x = c(1, 2), y = c(1, 10))
  ) +
  annotate(
    "textsegment",
    x = 1, xend = 2, y = 1, yend = 10,
    label = "10x increase", arrow = arrow()
  )

The graphical object should consist of 4 points, two of which for the path before the text and another two points for after the text. This seems to be correct as far is I can tell.

g <- layer_grob(last_plot(), 2)[[1]]
g <- grid::makeContent(g)$children[[1]]

g$x
#> [1] 1.82535885167464inches 3.19303238122172inches 3.80683014391654inches
#> [4] 5.17464114832536inches
g$y
#> [1] 0.681818181818182inches 2.35233370719354inches  3.10204383162793inches 
#> [4] 4.77272727272727inches

^{Created on 2022-02-04 by the reprex package (v2.0.1)}

Whereas with ragg everything goes fine:

[erikvona]

Thanks for the swift reply! While it would be nice to get this fixed for others (regardless of whether it's a bug in this package or in the Windows default graphics device), now I can make the plot I wanted using ragg.

[AllanCameron]

Although this is a quirk in the Windows device, we can track it down specifically to how it handles multiple arrow specifications for a polylinegrob. In particular, it seems to be thrown by having an NA passed as one of the angle arguments.

If I start by recreating the plot:

library(geomtextpath)
#> Loading required package: ggplot2
library(grid)

ggplot(mapping = aes(x, y)) +
  geom_col(
    data = data.frame(x = c(1, 2), y = c(1, 10))
  ) +
  annotate(
    "textsegment",
    x = 1, xend = 2, y = 1, yend = 10,
    label = "10x increase", arrow = arrow()
  )

Now we'll isolate the textpath and get it to generate grobs through makeContent

g <- layer_grob(last_plot(), 2)[[1]]
g <- grid::makeContent(g)

grid.newpage()
grid.draw(g$children)

Where we can see the problem persists.

Now if we look at the arrow argument

g$children[[1]]$arrow
#> $angle
#> [1] NA 30
#> 
#> $length
#> [1] 0.25inches 0.25inches
#> 
#> $ends
#> [1] 2 2
#> 
#> $type
#> [1] 1 1
#> 
#> attr(,"class")
#> [1] "arrow"

We will see that the first arrow isn't drawn because its angle is NA.

I'm not sure whether handling multiple arrow arguments, one of which is NA, is a defined behaviour in a polyline grob. Therefore, we could fix this problem by changing the angle = NA method of switching off the arrow to giving it a length value of 0:

g$children[[1]]$arrow$angle <- c(30, 30)
g$children[[1]]$arrow$length <- unit(c(0, 0.25), "in")

grid.newpage()
grid.draw(g$children)

There is no guarantee that this case would be handled well by other / future graphics devices, so I would be inclined to consider this a fixable bug in our code.

^{Created on 2022-02-04 by the reprex package (v2.0.1)}

[teunbrand]

Nice sleuthing Alan! I'll PR in a fix