Colorbar created with `legendry::guide_colbar` and `ggplot2::scale_color/fill_gradient2` not rendered correctly in version 1.4.0

[trekonom]

"Diverging" colorbars created with legendry::guide_colbar and scale_color/fill_gradient2 are no longer rendered correctly in ragg version 1.4.0, i.e. the "upper" part of the colorbar looks like a binned guide, whereas the "lower" one is fine.

Not sure whether this is an issue on side of ragg as the issue does not arise with e.g. ggplot2::guide_colorbar, but as the same code worked fine with version 1.3.3 ...

library(legendry)
#> Loading required package: ggplot2
library(ragg)

packageVersion("legendry")
#> [1] '0.2.1'
packageVersion("ragg")
#> [1] '1.4.0'

p <- ggplot(mtcars, aes(mpg, hp, color = cyl)) +
  geom_point() +
  scale_color_gradient2(
    midpoint = 6,
    guide = guide_colbar()
  )

file <- tempfile(fileext = ".png")
ggsave(file, device = ragg::agg_png)
#> Saving 7 x 5 in image

knitr::include_graphics(file)

^{Created on 2025-05-28 with reprex v2.1.1}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value
#>  version  R version 4.4.3 (2025-02-28)
#>  os       macOS Sequoia 15.5
#>  system   aarch64, darwin20
#>  ui       X11
#>  language (EN)
#>  collate  en_US.UTF-8
#>  ctype    en_US.UTF-8
#>  tz       Europe/Berlin
#>  date     2025-05-28
#>  pandoc   3.4 @ /Applications/RStudio.app/Contents/Resources/app/quarto/bin/tools/aarch64/ (via rmarkdown)
#>  quarto   1.6.39 @ /usr/local/bin/quarto
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package      * version date (UTC) lib source
#>  cli            3.6.5   2025-04-23 [1] CRAN (R 4.4.1)
#>  curl           6.2.3   2025-05-24 [1] CRAN (R 4.4.1)
#>  dichromat      2.0-0.1 2022-05-02 [1] CRAN (R 4.4.0)
#>  digest         0.6.37  2024-08-19 [1] CRAN (R 4.4.1)
#>  dplyr          1.1.4   2023-11-17 [1] CRAN (R 4.4.0)
#>  evaluate       1.0.3   2025-01-10 [1] CRAN (R 4.4.1)
#>  farver         2.1.2   2024-05-13 [1] CRAN (R 4.4.0)
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#>  ggplot2      * 3.5.2   2025-04-09 [1] CRAN (R 4.4.1)
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#>  knitr          1.50    2025-03-16 [1] CRAN (R 4.4.1)
#>  labeling       0.4.3   2023-08-29 [1] CRAN (R 4.4.0)
#>  legendry     * 0.2.1   2025-03-04 [1] CRAN (R 4.4.1)
#>  lifecycle      1.0.4   2023-11-07 [1] CRAN (R 4.4.0)
#>  magrittr       2.0.3   2022-03-30 [1] CRAN (R 4.4.0)
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#>  R6             2.6.1   2025-02-15 [1] CRAN (R 4.4.1)
#>  ragg         * 1.4.0   2025-04-10 [1] CRAN (R 4.4.1)
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#> 
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#>  * ── Packages attached to the search path.
#> 
#> ──────────────────────────────────────────────────────────────────────────────

And as a reference, using ragg version 1.3.3 gives the desired result:

library(legendry)
#> Loading required package: ggplot2
library(ragg)

packageVersion("legendry")
#> [1] '0.2.1'
packageVersion("ragg")
#> [1] '1.3.3'

p <- ggplot(mtcars, aes(mpg, hp, color = cyl)) +
  geom_point() +
  scale_color_gradient2(
    midpoint = 6,
    guide = guide_colbar()
  )

file <- tempfile(fileext = ".png")
ggsave(file, device = ragg::agg_png)
#> Saving 7 x 5 in image

knitr::include_graphics(file)

^{Created on 2025-05-28 with reprex v2.1.1}

[thomasp85]

@teunbrand do you have a good explanation for this behaviour. I have not touched the gradient rendering in ragg in ages

[teunbrand]

I do not have a good explanation. The same happens in ggplot2 if you use display = "gradient" in the colour bar so the issue doesn't stem from legendry and it most likely is gradient rendering. Here is a pure grid example where gradient rendering runs amock.

library(grid)
library(scales)

file <- tempfile(fileext = ".png")
ragg::agg_png(file)

gradient <- rectGrob(
  gp = gpar(
    fill = linearGradient(pal_div_gradient()(seq(0, 1, length.out = 7)))
  )
)
grid.newpage()
grid.draw(gradient)

dev.off()
#> png 
#>   2
knitr::include_graphics(file)

^{Created on 2025-05-28 with reprex v2.1.1}

(If you have to touch gradient rendering, I'd like to drop a subtle hint for keeping an eye out for #154 😁)

[thomasp85]

What do you know... I did touch that code in the last release cycle. This is due to my fix for #177

[trekonom]

Thanks both of you for having a look and the quick fix.