Compute ggsave() dimensions for a fixed panel content area

Given a fitted ggplot, returns width and height values such that, when passed to ggplot2::ggsave(), the resulting file has a panel content area matching width / height. The "panel content area" is the rectangular bounding box of the gtable cells tagged panel — i.e., the smallest rectangle that encloses every plotting panel. Whatever grobs fall inside that rectangle (e.g., inter-panel gutters and strip rows that sit between facet rows) are counted as part of the target; everything outside it (axes, axis titles, plot title, caption, legend, plot margins, and any strips that sit above/below or beside the panel block such as facet_grid side strips) is counted as chrome.

Usage

hv_ggsave_dims(plot, width, height, units = c("in", "cm", "mm"))

Arguments

plot

A ggplot (or patchwork) object.

width

Target panel content area width, in units.

height

Target panel content area height, in units.

units

One of "in", "cm", "mm". Default "in".

Value

A named list with elements width, height, units — shaped to splat directly into ggplot2::ggsave() via do.call() (see examples).

Details

Useful for multi-panel figure sets where a constant data region is required across PDFs regardless of label length or legend placement. Always measured with a PDF sizing device, which is why units is limited to length (inches, cm, mm) — DPI is irrelevant for vector output.

Examples

if (FALSE) { # \dontrun{
p <- ggplot2::ggplot(mtcars, ggplot2::aes(hp, mpg)) +
  ggplot2::geom_point() +
  ggplot2::labs(title = "Long title that eats vertical space",
                x = "Horsepower", y = "Miles per gallon")

dims <- hv_ggsave_dims(p, width = 4, height = 3)
do.call(
  ggplot2::ggsave,
  c(list(filename = "fig.pdf", plot = p), dims)
)
} # }