Inverted raster images

[debruine]

When displaying the background image in a ggplot using annotation_custom() and a rasterGrob, the image is inverted if the y-axis is reversed, but only when ragg is the graphics device. This doesn't happen with other graphics devices like quartz_png, which show the image upright. So the same code can produce different graphs depending on the render environment (e.g., knitr vs pkgdown).

See https://debruine.github.io/imginv/articles/test.html for a demonstration of the problem in situ.

This should reproduce the problem.

library(ggplot2) # also uses functions from ragg and grid

# set up raster image and plot
grad <- matrix(hcl(seq(0, 280, 40), 80, 80), nrow=8, ncol=5)
img <- grid::rasterGrob(grad)
width <- 500
height <- 800

p <- ggplot() +
  scale_y_reverse() + # this is the problem
  coord_fixed(xlim = c(0, width),
              ylim = c(0, height)) +
  annotation_custom(img, 0, width, -height, 0) +
  geom_point(aes(x, y), data.frame(x = 0, y = 0))

# displays red on top - correct
# if your computer is different from mine, this might need to have another graphics device set
# but I don't know how to do that outside knitr options, quartz_png shows the image upright
p 

# displays purple on top
file <- tempfile(fileext='.png')
ragg::agg_png(file, width = width, height = height, res = 72)
p
dev.off()
browseURL(file)

[thomasp85]

This is the file I get when rendering to png with your code (the last part, using ragg)... Is this not what is expected?

[thomasp85]

It is the same output as both quartz and Cairo on my computer (I know this is borderline "works on my computer" comment, but it's just for reference :-)

[debruine]

For me, purple is on top and also the y axis is inverted - 0 on top and the plotted point in the upper left. I’m not sure how your image is ignoring the scale_y_reversed() part of the plot.

…

On 19 Nov 2020, at 07:36, Thomas Lin Pedersen ***@***.***> wrote:  This is the file I get when rendering the file with your code (the last part, using ragg)... Is this not what is expected? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[thomasp85]

Ah - I was on the dev version of ggplot2... (FYI, setting the limits in the coord may end up affecting the direction of the scale in future versions)

[thomasp85]

I can reproduce now, though it is somewhat inconclusive...

ragg:

quartz (default macOS):

cairo:

I would say that it is actually a bug in Quartz, not in ragg and cairo.

[thomasp85]

However, you may be right that you wouldn't expect scale_y_reverse() to flip the raster - that would be a ggplot2 issue I think

[thomasp85]

Do you have access to a windows machine? What is the behaviour of the default windows device in case you can test?

[debruine]

Thanks for looking into this. Seems I lucked into the one device that did what I want. I don't have easy access to a windows machine, sorry.

The context is plotting face images with a pre-existing associated coordinate system that starts in the upper left. I guess I'll just switch the plotting function to reverse the y coordinates, since I don't normally include the axes.

[thomasp85]

Yeah, I agree that the behaviour is unwanted, but it should be fixed in ggplot2, not in the device