Bug when rendering `grid::radialGradient()`

[teunbrand]

In the image below, I'd have expected the outside to be green, and a smooth interpolation between "tomato" and "dodgerblue" (instead of the sudden switch from magenta to blue).

library(grid)

colours <- c("tomato", "dodgerblue", "limegreen")

radial <- radialGradient(colours, group = FALSE)
rect <- rectGrob(gp = gpar(fill = radial))

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

grid.newpage()
grid.draw(rect)

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

^{Created on 2025-08-08 with reprex v2.1.1}

Expected image (with png(type = "cairo")):

[Breeze-Hu]

It appears that grid::linearGradient() also exhibits similar rendering issues:

library(grid)

grid.rect(
    gp = gpar(fill = linearGradient(c("blue", "yellow")))
)

agg:

Cairo:

[thomasp85]

I can't reproduce this... Are you using the latest version of ragg? Also, (though it shouldn't matter). Are you both on windows?

[teunbrand]

Yes, I'm using ragg 1.4.0 on Windows 11.
The linearGradient() examples also render as Breeze-Hu shows on my machine.

[Breeze-Hu]

Hi, Thomas!

I recorded the screen.
Interestingly, this result cannot be reproduced using reprex::reprex(). Could it be because reprex rendering doesn't use the user-configured backend?

https://drive.google.com/file/d/1M0N6gq6GcUDmDqMtAsPyN9J8Wa-NacdN/view?usp=share_link

[thomasp85]

can you try with the dev version (is what I meant) - I did touch the AGG gradient code some time ago

[Breeze-Hu]

ohhh sorry! I misunderstood.
Great! The issue is resolved(at least on my device).

I can happily use Ragg for rendering again! 😁

[Breeze-Hu]

Thanks!

[teunbrand]

Confirming from my end that the dev version seems to work fine. Thanks Thomas!

[Breeze-Hu]

Hello! Although this issue has already been resolved, I later noticed some subtle problems with ragg’s rendering.

As shown in the figure, what should be a smooth linear color transition appears with slight “banding” when rendered with ragg, whereas it looks perfectly smooth with Quartz.

I’m not sure if this is related to ragg’s gradient code — could you test this on your side?

library(ggplot2)

colors <- grid::linearGradient(
  c("white", "#f6915e"),
  stops = seq(0, 1, length.out = 2),
  x1 = unit(0, "npc"),
  y1 = unit(0, "npc"),
  x2 = unit(0, "npc"),
  y2 = unit(1, "npc"),
)


ggplot(mtcars, aes(mpg, wt)) +
  geom_rect(
    aes(xmin = I(0.2), xmax = I(0.5), ymin = I(0), ymax = I(1)),
    fill = fill_alpha(colors, alpha = 0.2)
  )

ragg result:

Quartz result:

sessionInfo()

R version 4.5.1 (2025-06-13)
Platform: aarch64-apple-darwin20
Running under: macOS Sequoia 15.6.1

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib 
LAPACK: /Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.12.1

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

time zone: Asia/Shanghai
tzcode source: internal

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

other attached packages:
[1] ggplot2_4.0.0

loaded via a namespace (and not attached):
 [1] labeling_0.4.3     RColorBrewer_1.1-3 R6_2.6.1           tidyselect_1.2.1  
 [5] farver_2.1.2       magrittr_2.0.3     gtable_0.3.6       glue_1.8.0        
 [9] tibble_3.3.0       dichromat_2.0-0.1  pkgconfig_2.0.3    generics_0.1.4    
[13] dplyr_1.1.4        lifecycle_1.0.4    cli_3.6.5          S7_0.2.0          
[17] scales_1.4.0       grid_4.5.1         vctrs_0.6.5        textshaping_1.0.3 
[21] withr_3.0.2        systemfonts_1.2.3  compiler_4.5.1     rstudioapi_0.17.1 
[25] tools_4.5.1        ragg_1.5.0         pillar_1.11.0      rlang_1.1.6