ggplots are rendered three times on the RStudio graphics device at two different sizes

[paleolimbot]

This is something @thomasp85 noticed at Tidy Dev Day when he was helping Edzer and I with lazy raster rendering. He noticed the makeContext method for my custom grob was getting called three times when displaying the plot interactively (using profvis). Two of the three draw calls assume a lower screen resolution. Clicking "Zoom" for any grob results in two additional render calls instead of the expected one (for all grobs), and gtables (but not ggplots) are always rendered twice (even in R Notebooks). I imagine the code to fix this isn't in ggplot2, but I have no idea where that code is.

For context, this all comes out of trying to get (possibly huge) rasters to render in a reasonable amount of time in an interactive session for r-spatial/stars#21. This is the reprex I used to test this below:

library(ggplot2)
library(grid)

log_file <- "log.txt"
unlink(log_file)
makeContext.lazyGrob <- function(x) {
  size <- dev.size(units = "px")
  write(sprintf("Drawing %s at %sx%s", x$test, size[1], size[2]), log_file, append = TRUE)
  x
}

GeomPoint2 <- ggproto(
  "GeomPoint2", GeomPoint,
  draw_panel = function(self, data, panel_params, coord, na.rm = FALSE) {
    layer_grob <- ggproto_parent(GeomPoint, self)$draw_panel(data, panel_params, coord)
    gTree(test = "ggplot", children = gList(layer_grob), cl = "lazyGrob")
  }
)

geom_point2 <- function() {
  layer(geom = GeomPoint2, stat = "identity", position = "identity")
}

# log grid drawing
grid.newpage()
grid.draw(gTree(test = "grid", cl = "lazyGrob"))

# log gtable drawing
grid.newpage()
grid.draw(
  gtable::gtable_row(
    "test", 
    grobs = list(gTree(test = "gtable", cl = "lazyGrob")), 
    widths = unit(1, "npc")
  )
)

# log ggplot drawing
ggplot(mpg, aes(cty, hwy)) +
  geom_point2()

# view the log
cat(paste(readLines(log_file), collapse = "\n"))
#> Drawing grid at 504x360
#> Drawing gtable at 504x360
#> Drawing gtable at 504x360
#> Drawing ggplot at 504x360

[thomasp85]

Thanks for reminding me of this. I’ll tackle this as part of the performance overhaul

[clauswilke]

I've noticed an issue that I believe is related: When you interactively resize the plot window containing a grob that is slow to make its content, sometimes the final render doesn't complete and you end up with a distorted version of the plot. It looks like the resizing first rescales a bitmap version of the plot and then rerenders it, and the final render can fail. Resizing again usually fixes the problem.