animation.hook is ignored for LaTeX output in the knitr engine

[cderv]

The animation.hook chunk option works for HTML output but has no effect for LaTeX/PDF output.

For a chunk with fig.show: animate, we only inject a default hook when the format is not LaTeX

quarto-cli/src/resources/rmd/hooks.R

Lines 115 to 126 in d4cb49f

	# automatically set gifski hook for fig.animate
	opts_hooks[["fig.show"]] <- function(options) {
	# get current value of fig.show
	fig.show <- options[["fig.show"]]
	# use gifski as default animation hook for non-latex output
	if (identical(fig.show, "animate")) {
	if (
	!is_pandoc_latex_output(format) && is.null(options[["animation.hook"]])
	) {
	options[["animation.hook"]] <- "gifski"
	}

The HTML branch then delegates to knitr's hook_animation(), so a user-supplied hook is honored there. The LaTeX branch instead calls our own latex_animation(), which always emits \animategraphics{} and never looks at animation.hook

quarto-cli/src/resources/rmd/hooks.R

Lines 1170 to 1206 in d4cb49f

	# ported from:
	# https://github.com/yihui/knitr/blob/f8f90baad99d873202b8dc8042eab7a88fac232f/R/hooks-latex.R#L151-L171
	latex_animation <- function(x, options) {
	fig.num = options$fig.num %||% 1L
	ow = options$out.width
	# maxwidth does not work with animations
	if (identical(ow, '\\maxwidth')) {
	ow = NULL
	}
	if (is.numeric(ow)) {
	ow = paste0(ow, 'px')
	}
	size = paste(
	c(
	sprintf('width=%s', ow),
	sprintf('height=%s', options$out.height),
	options$out.extra
	),
	collapse = ','
	)
	aniopts = options$aniopts
	aniopts = if (is.na(aniopts)) NULL else gsub(';', ',', aniopts)
	size = paste(c(size, sprintf('%s', aniopts)), collapse = ',')
	if (nzchar(size)) {
	size = sprintf('[%s]', size)
	}
	sprintf(
	'\\animategraphics%s{%s}{%s}{%s}{%s}',
	size,
	1 / options$interval,
	sub(sprintf('%d$', fig.num), '', xfun::sans_ext(x)),
	1L,
	fig.num
	)
	}

It also adds a dependency on the LaTeX animate package unconditionally

quarto-cli/src/resources/rmd/hooks.R

Lines 713 to 718 in d4cb49f

	# check for latex
	if (is_pandoc_latex_output(format)) {
	# include dependency on animate package
	knitr::knit_meta_add(list(
	rmarkdown::latex_dependency("animate")
	))

Upstream knitr changed this in yihui/knitr#2452: hook_plot_tex() now calls a user-supplied animation.hook (or the package option animation.fun) to generate the LaTeX code, so LaTeX packages other than animate can be used, xmpmulti for beamer overlays being the motivating example. The built-in hooks (ffmpeg, gifski, scianimator, r2swf) generate HTML and keep being ignored for LaTeX. Our latex_animation() is a port of knitr's code from before that change.

So with the next knitr release this will work in .Rmd but not in .qmd.

We could port the same logic into latex_animation(): when animation.hook is a function and is not one of knitr's built-in HTML hooks, call it instead of emitting \animategraphics{}, and skip the animate dependency in that case.

Two things to sort out if we do this. Our schema documents animation-hook with default: ffmpeg while we actually inject gifski for non-LaTeX output, and it is typed as a string with completions, so a function can only be passed with the classic R chunk syntax ({r, animation.hook=my_hook}) and not with #| YAML.

quarto-cli/src/resources/schema/cell-figure.yml

Lines 219 to 235 in d4cb49f

	- name: animation-hook
	tags:
	engine: knitr
	schema:
	string:
	completions: [ffmpeg, gifski]
	default: ffmpeg
	description:
	short: "Hook function to create animations in HTML output"
	long: |
	Hook function to create animations in HTML output.
	The default hook (`ffmpeg`) uses FFmpeg to convert images to a WebM video.
	Another hook function is `gifski` based on the
	[**gifski**](https://cran.r-project.org/package=gifski) package to
	create GIF animations.