Using RGL in pkgdown web sites

What is the problem?

pkgdown is an R package that makes it easy to build a web site for your package. However, the current version 1.6.1 on CRAN doesn’t work so well for packages whose examples use RGL or other packages like leaflet that use htmlwidgets. This document describes current progress in supporting both of these.

The main problem for pkgdown support is that RGL and other htmlwidgets users require multiple Javascript libraries to be linked to each web page. pkgdown 1.6.1 can’t do this, but the current development version on Github adds support for additional dependent libraries. This also require downlit version 0.4.0 or higher.

Installing the changes

Installing the changes is fairly easy. Make sure you have the remotes package installed, then run

remotes::install_github(c("rstudio/webshot2",
                          "rstudio/chromote",
                          "r-lib/pkgdown"))

With these development version packages installed, you should see RGL or leaflet output appear automatically in examples. The RGL output is set up to mimic what would happen in a knitr document that uses

setupKnitr(autoprint = TRUE)

i.e. the output RGL commands will automatically be included in the display. Low-level changes will be collected into a single display:

# Show regression plane with z as dependent variable
library(rgl)
open3d()

## null 
##   15

x <- rnorm(100)
y <- rnorm(100)
z <- 0.2*x - 0.3*y + rnorm(100, sd = 0.3)
fit <- lm(z ~ x + y)

plot3d(x, y, z, type = "s", col = "red", size = 1)

# No plot here, because of the planes3d() call below

coefs <- coef(fit)
a <- coefs["x"]
b <- coefs["y"]
c <- -1
d <- coefs["(Intercept)"]
planes3d(a, b, c, d, alpha = 0.5)

Specifying the size of figures

By default, pkgdown generates standard plots which are wider than they are high (according to the golden ratio). Often RGL plots look better with equal width and height, since the contents may be rotated by the user.

To specify the size of plots in pkgdown, you use the figures entry in _pkgdown.yml. The defaults are similar to

figures:
  dev: ragg::agg_png
  dpi: 96
  dev.args: []
  fig.ext: png
  fig.width: 7
  fig.height: ~
  fig.retina: 2
  fig.asp: 1.618
  bg: NA
  other.parameters: []

By default RGL uses these parameters as well, but allows you to override any of fig.width, fig.height and fig.asp by specifying an rgl entry in other.parameters. For example:

figures:
  fig.width: 5
  other.parameters:
    rgl:
      fig.asp: 1

This will make all plots have a width of 5 inches and will make RGL plots square.

Is this safe to use?

These are development versions of the packages, so they may contain bugs, either in my changes or in other unreleased changes. I don’t recommend you use them in regular production code. To re-install released versions of the packages, run

install.packages(c("pkgdown", "rgl"))

If you do use them and notice any bugs, please report them!