poppler (cairo) backend pdf viewer bug when viewing 'pdf()' device output with alpha masks

trevorld / ggpattern

ggplot geoms with pattern fills

https://trevorldavis.com/R/ggpattern/dev/

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poppler (cairo) backend pdf viewer bug when viewing 'pdf()' device output with alpha masks #70

Closed trevorld closed 2 years ago

trevorld commented 2 years ago

library(ggplot2)
library(sf)
library(rnaturalearth)
library(ggpattern)

shapefile <- ne_countries(continent = 'europe', returnclass = "sf", scale = 110)

options(ggpattern_use_R4.1_masks = TRUE)
pdf("mask_bug.pdf")
ggplot(shapefile) +
  geom_sf_pattern(aes(geometry = geometry, fill = name, pattern_fill = name),
                  size = 4, 
                  pattern = "stripe") +
  xlim(-10, 30) +
  ylim( 37, 60) +
  theme_bw() +
  theme(legend.position = 'none')
dev.off()

pdf_masking_bug

Workarounds

Use ragg::agg_png() or perhaps rasterpdf::agg_pdf() instead
Set options(ggpattern_use_R4.1_masks = FALSE) to use the raster masking alternative to the R 4.1 masking feature

trevorld commented 2 years ago

Apparently this is a pdf viewer bug in evince (my default pdf viewer) and not a bug in the pdf file. The pdf looks fine in other pdf viewers such as firefox and okular and reportedly xpdf and chrome.

trevorld commented 2 years ago

More minimal example of pdf output to explore pdf viewer bug with alpha masks:

library("grid")

x <- c(0.1, 0.9, 0.9, 0.1, 0.1, 0.3, 0.7, 0.7, 0.3, 0.3)
y <- c(0.1, 0.1, 0.9, 0.9, 0.1, 0.3, 0.3, 0.7, 0.7, 0.3)
id.lengths <- c(5L, 5L)
rule <- "evenodd"
gp <- gpar(fill = "black", lwd = 0L)
masker <- pathGrob(x, y, id.lengths = id.lengths, rule = "evenodd", gp = gp)

masked <- rectGrob(height = unit(0.7, "npc"),
                   gp = gpar(fill = "yellow", lwd = 4, col = "blue"),
                   vp = viewport(mask = masker))

grDevices::pdf("mask_bug.pdf")
grid.draw(masked)
dev.off()

Looking at the output of pdftocairo -png -f 1 -l 1 mask_bug.pdf -o cairo-output and pdftoppm -png -f 1 -l 1 mask_bug.pdf -o splash-output it appears that the bug is in poppler's "cairo" backend and not poppler's "splash" backend. This is why the pdf looks fine in okular (uses poppler's "splash" backend) but not evince (uses poppler's "cairo" backend) even though both use poppler as their pdf backend.

trevorld commented 2 years ago

Bug reported upstream to poppler: https://gitlab.freedesktop.org/poppler/poppler/-/issues/1202

kongdd commented 2 years ago

Is this problem solved?

trevorld commented 2 years ago

Is this problem solved?

You mean have poppler developers fixed the bug upstream? Haven't seen any evidence that they have done so. It may actually be a bug in Cairo but either way the evince snap provided by Ubuntu still has the bug. If I compile poppler manually with the Cairo headers available by apt in Ubuntu 20.04 LTS I still get the bug.
R Core considers this a bug in poppler and won't be implementing a hack on their end in grDevices::pdf() to work around it
You can avoid this problem by:

1) Turn off the alpha mask optimization: options(ggpattern_use_R4.1_masks = FALSE) (this will slow down rendering) 2) Use a different graphics device like ragg::agg_png() or perhaps grDevices::cairo_pdf() (but note with the latter if you haven't upgraded to R 4.2 then you may hit a limit in Cairo devices on number of masks #59) 3) Use a different pdf viewer like okular, firefox, google-chrome, etc.

kongdd commented 2 years ago

@trevorld Thanks for your detailed explanation.

1.1 options(ggpattern_use_R4.1_masks = F) and grDevices::cairo_pdf: In this situation, pattern is not in vector form, and looks blurry.
1.2 options(ggpattern_use_R4.1_masks = T) and grDevices::cairo_pdf: Mask is error.
2.1 options(ggpattern_use_R4.1_masks = F) and Cairo::CairoPDF:
2.2 options(ggpattern_use_R4.1_masks = T) and Cairo::CairoPDF: Same error as 2.1

kongdd commented 2 years ago

I need a line pattern. Any idea how to make it?

trevorld commented 2 years ago

1.1, 2.1, 2.2 - Yes, the non-alpha mask alternative is a rasterGrob() approximation. However you can increase the resolution via the pattern_res aesthetic or alternatively by setting the ggpattern_res option via options().

1.2 - The cairo_pdf() alpha mask error should theoretically go away if you upgrade to R 4.2

kongdd commented 2 years ago

Thanks for your solution. R 4.2 is not available on the official website. Do you know how to upgrade to 4.2? I am using ubuntu and win10.

trevorld commented 2 years ago

R 4.2 is currently known as "R-devel" and source code is available here: https://stat.ethz.ch/R/daily/
Should be straightforward to compile on Ubuntu i.e. something like ./configure; make; sudo make install

trevorld commented 2 years ago

Also {svglite} recently added support for the R 4.1 alpha masking feature. If you really need a vectorized image format could try saving an "svg" file with svglite::svglite() and then converting to pdf...