gdtools

gdtools addresses four practical problems when working with fonts in R:

Problem	gdtools solution
Measure text without a device: layout calculations (column widths, text wrapping) need reliable metrics independent of the rendering device	strings_sizes() via Cairo
Register non-system fonts: Google Fonts or Liberation fonts (bundled) must be made visible to ‘systemfonts’	font_set_liberation(), font_set_auto(), font_set()
Embed fonts in HTML: Shiny, R Markdown and girafe need htmlDependency objects so the browser loads the right fonts	font_set()$dependencies, gfontHtmlDependency(), liberation*HtmlDependency()
Check font availability: detect missing fonts before rendering, to avoid silent fallbacks	font_family_exists(), sys_fonts()

How font metric calculation works

gdtools was originally designed to compute font metrics for R graphic devices via C-level interfaces (Cairo and FreeType). With the arrival of the ‘systemfonts’ package, font discovery and matching became much simpler and the C interface was no longer needed by other packages.

The package has since been refocused. Font metric calculation follows two steps:

1. Font lookup: ‘systemfonts’ resolves the family name to a font file. Any font registered via systemfonts::register_font(), register_gfont(), or font_set() is found.
2. Metric computation: Cairo reads the font file and computes width, ascent, and descent.

The metrics are independent of any graphic device. Whether they match the final rendering depends on how the device resolves fonts on its side, this is a device concern.

Installation

You can install the released version of gdtools from CRAN with:

install.packages("gdtools")

And the development version from GitHub with:

# install.packages("remotes")
remotes::install_github("davidgohel/gdtools")

Font metrics

The main function for text measurement is strings_sizes(). It returns width, ascent and descent in inches using Cairo. The measurements are accurate for devices that use Cairo or ‘systemfonts’ for font resolution (ragg, svglite, ggiraph, cairo_pdf(), …); for devices with their own font engine (pdf(), png(), …) the metrics may not match the rendering.

library(gdtools)
strings_sizes(
  c("a string", "a longer string"),
  fontsize = 24, 
  bold = TRUE, 
  italic = TRUE
)
#>      width    ascent    descent
#> 1 1.203939 0.2413737 0.07259115
#> 2 2.315104 0.2413737 0.07259115

All arguments are vectorized:

strings_sizes(
  c("normal", "bold", "italic", "bold-italic"),
  fontsize = 12,
  bold = c(FALSE, TRUE, FALSE, TRUE),
  italic = c(FALSE, FALSE, TRUE, TRUE)
)
#>       width    ascent     descent
#> 1 0.5094401 0.1195475 0.003173828
#> 2 0.3517253 0.1199544 0.003092448
#> 3 0.3334147 0.1195475 0.002929688
#> 4 0.7870280 0.1206868 0.003092448

Font management

font_set_auto() detects the best available system fonts and falls back to Liberation fonts when needed. It returns a font_set object ready to use with ggplot2, ggiraph, or any ‘systemfonts’-based device:

library(gdtools)

fonts <- font_set_auto()
fonts
#> Font set
#>   sans:    Arial [system]
#>   serif:   Times New Roman [system]
#>   mono:    Courier New [system]
#>   symbol:  Symbol [system]
#>   4 HTML dependencies

For explicit control, font_set() lets you pick each role with font_google(), font_liberation(), or a plain family name:

fonts <- font_set(
  sans  = font_google("Open Sans"),
  mono  = font_liberation("mono")
)

fonts$sans          # "Open Sans"
fonts$dsvg_fonts    # named list for dsvg() / girafe()
fonts$dependencies  # list of htmlDependency objects

For an offline-only setup, font_set_liberation() uses Liberation fonts for all four roles:

fonts <- font_set_liberation()
fonts

Going further

Google Fonts

A set of lower-level functions is provided to download and cache fonts from ‘Google Fonts’. They can be used in ‘R Markdown’ documents and ‘Shiny’ applications, as well as with graphic outputs generated by ‘ggiraph’, ‘ragg’ and ‘svglite’, or tabular outputs from ‘flextable’.

# Download and register with systemfonts (cached for future use)
register_gfont(family = "Open Sans")

Use addGFontHtmlDependency() to embed a Google Font in an HTML document, and gfontHtmlDependency() to create an htmltools dependency object.

To install a Google Font at the system level (e.g. in a Dockerfile), use install_gfont_script():

install_gfont_script("Fira Sans", platform = "debian", file = "install-font.sh")

Liberation fonts

The package bundles ‘Liberation Sans’, ‘Liberation Serif’ and ‘Liberation Mono’ fonts (SIL Open Font License). They are useful as cross-platform fallback fonts, for visual tests, or when no internet connection is available.

font_set_liberation() registers all three families with ‘systemfonts’ and produces the matching HTML dependencies in a single call:

fonts <- font_set_liberation()
fonts$sans
fonts$dependencies

The individual functions register_liberationsans(), register_liberationserif() and register_liberationmono() remain available when only a specific variant is needed.