Font recipes

Measurement vs rendering

Using fonts with ‘munch’ involves two independent steps:

1. Measurement, ‘munch’ calls gdtools::strings_sizes() to compute text metrics (width, ascent, descent). Under the hood, ‘systemfonts’ locates the font file, then Cairo calculates the metrics. Any font registered via systemfonts::register_font(), gdtools::register_gfont(), gdtools::font_set(), gdtools::font_set_liberation() or gdtools::font_set_auto() is found at measurement time.

2. Rendering, the graphic device draws the text. Each device has its own way of resolving font names. This is where mismatches happen: a font that measurement found may be invisible to the device, or vice versa.

When both steps find the same font, the output is correct. When they disagree, text is positioned using one font’s metrics but drawn with another ; leading to overlapping, clipping or misaligned labels.

Which devices agree with measurement?

Device family	Font lookup	Agrees with measurement?
ragg, svglite, ggiraph	‘systemfonts’	Always, same lookup on both sides
cairo_pdf(), png(type = "cairo")	fontconfig	Only for system-installed fonts
pdf(), png(), jpeg()	Own engine	No guarantee, needs ‘extrafont’

systemfonts devices (recommended)

Devices from ragg, svglite and ggiraph use ‘systemfonts’ for both measurement and rendering. Every registered font is visible on both sides.

The simplest approach is font_set_liberation(), which registers Liberation Sans, Serif and Mono in a single call, no internet needed, SIL Open Font License:

library(gdtools)
font_set_liberation()

For system-aware detection (Arial, Helvetica, etc. with Liberation as fallback), use font_set_auto():

font_set_auto()

For specific fonts (e.g. a Google Font), use font_set():

library(munch)
library(ggplot2)

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

ggplot(mtcars, aes(mpg, wt)) +
  geom_point() +
  labs(title = "**Open Sans** via *font_set()*") +
  theme_minimal(base_family = fonts$sans) +
  theme(plot.title = element_md())

Cairo devices

Cairo devices (cairo_pdf(), png(type = "cairo")) use the same Cairo engine for rendering as ‘gdtools’ uses for measurement. However, font lookup differs: measurement goes through ‘systemfonts’, rendering goes through fontconfig. Fontconfig only scans system-installed fonts.

This means:

• System fonts (e.g. Arial, Helvetica), measurement and rendering agree. Everything works.
• Google Fonts via register_gfont(), found by measurement but not necessarily by fontconfig, depending on where the cache is.
• Liberation fonts via font_set_liberation() (or individual register_liberation*()), found by measurement only. Rendering falls back silently unless the fonts are also installed at the OS level.

Use font_family_exists(system_only = TRUE) to check whether a font will be found by fontconfig:

library(gdtools)

# Found by measurement (systemfonts + registry)?
font_family_exists("sans")
#> [1] TRUE

# Found by fontconfig (system-installed only)?
font_family_exists("sans", system_only = TRUE)
#> [1] TRUE

Standard R devices and extrafont

Standard devices (pdf(), png(), jpeg()) use their own font engine and ignore ‘systemfonts’ entirely.

‘munch’ uses ‘gdtools’ (which relies on Cairo) for text measurement. The standard pdf() device uses its own font engine. For the output to be correct, the fonts used by ‘munch’ must also be known to pdf().

The ‘extrafont’ package bridges this gap: it imports TrueType fonts into R’s PDF device by generating font metric files that pdf() can use.

The key requirement: every font used in the plot must be available to both ‘systemfonts’ (for measurement) and pdf() (for rendering). If a font is registered with ‘systemfonts’ but not with pdf(), the text metrics will not match the rendering and the output will have positioning errors.

Example: exporting a munch plot to PDF

library(gdtools)
library(munch)
library(ggplot2)

df <- data.frame(
  x = 1:3,
  y = 1:3,
  label = c("**Bold**", "*Italic*", "`Code`")
)

p <- ggplot(df, aes(x, y, label = label)) +
  geom_label_md(code_font_family = "Courier New") +
  theme_minimal(base_family = "Arial")

# Make Arial and Courier New available to pdf()
library(extrafont)
# font_import()
# Run font_import() once to scan system fonts,
# then loadfonts() in each session.
loadfonts()

# Suppress the device warning since we ensured font concordance
options(munch.skip_device_check = TRUE)

pdf(file = "munch-example.pdf", width = 7, height = 7)
print(p)
dev.off()

The steps are:

1. Install fonts at the system level, both “Arial” and “Courier New” must be installed as system fonts.
2. Import fonts once with extrafont::font_import(), this scans system fonts and creates metric files for pdf(). Only needed once.
3. Load fonts each session with extrafont::loadfonts(), this registers the imported fonts with pdf() for the current session.
4. Disable the device check with options(munch.skip_device_check = TRUE), since you have ensured font concordance manually, the warning is no longer needed.

Note: cairo_pdf() is a simpler alternative. It uses Cairo for rendering (same engine as ‘gdtools’ for measurement), so system-installed fonts work without ‘extrafont’. Use pdf() + ‘extrafont’ only when cairo_pdf() is not available.

Font sources at a glance

Font source	Measurement	ragg / svglite / ggiraph	Cairo devices	pdf() / png()
System font	Yes	Yes	Yes	Via extrafont
register_gfont()	Yes	Yes	Depends on cache location	No
font_set_liberation()	Yes	Yes	No (unless OS-installed)	No
font_set_auto()	Yes	Yes	System fonts only	No
font_set()	Yes	Yes	System fonts only	No

Diagnosing font problems

When text looks wrong (wrong font, misaligned labels), the cause is almost always a measurement/rendering disagreement. Here is a quick checklist:

1. Is the font found by measurement?

   gdtools::font_family_exists("My Font")

   If FALSE: the font is not registered with ‘systemfonts’. Register it with register_gfont(), font_set(), or systemfonts::register_font().

2. Is the font found by the device?

   • For Cairo devices:

     gdtools::font_family_exists("My Font", system_only = TRUE)

     If FALSE: the font is not system-installed. Either install it at the OS level or switch to a ‘systemfonts’ device (ragg, svglite).

   • For pdf(): check that extrafont::fonts() includes the family.

   • For ragg/svglite/ggiraph: if step 1 passed, this always works.

3. Do both sides find the same font? Even when both find a font, it may not be the same file (e.g. a different weight or a substitution). Compare:

   # What systemfonts resolves
   systemfonts::match_fonts("My Font")
   
   # What's installed at the system level
   subset(systemfonts::system_fonts(), family == "My Font")