knitr::opts_chunk$set(collapse = T, comment = "#>") library("svglite")
svglite produces SVG files containing plain text but fonts are still
important for plot generation and rendering. Fonts are used during SVG
generation to figure out the metrics of graphical elements. The font
name is then recorded in the font-family
property of text anchors so
that SVG renderers know what fonts to use. svglite does try to ensure
a consistent figure rendering even when fonts are not available at the
time of rendering (by supplying the
textLength
SVG text attribute). However, the text may look slightly distorted
when a fallback font is used. This means that for optimal display,
the font must be available on both the computer used to create the
svg, and the computer used to render the svg. The defaults are fonts
that are available on almost all systems: there may be small
differences between them, but they are unlikely to cause problems in
most causes.
| R family | Font on Windows | Font on Unix |
|----------|--------------------|--------------|
| sans
| Arial | Arial |
| serif
| Times New Roman | Times |
| mono
| Courier | Courier |
| symbol
| Standard Symbols L | Symbol |
One downside to these default fonts is that they do not have good
coverage of characters for non-latin alphabets. This can be fixed by
using the arguments system_fonts
and user_fonts
which provide
control over which fonts to use during SVG generation and rendering.
system_fonts
takes a named list of font families as argument. The
names typically correspond to standard R faces but they can also alias
non-standard families (though this is less useful):
fonts <- list( sans = "Helvetica", mono = "Consolas", `Times New Roman` = "DejaVu Serif" ) ss <- svgstring(system_fonts = fonts) plot(1:10) text(0.8, 0.8, "Some text", family = "mono") text(0.2, 0.2, "Other text", family = "Times New Roman") dev.off() ss()
If you need support for non-latin characters, choose fonts with good Unicode coverage. "Arial Unicode MS" is a sans serif font with good coverage that is available on macOS and Windows systems (on the latter, only if MS Office is installed). Note that this font does not support kerning and has no bold or italic faces.
svglite("Rplots.svg", system_fonts = list(sans = "Arial Unicode MS")) plot.new() text(0.5, 0.5, "正規分布") dev.off()
The Noto fontset provided by Google as well as the Han Sans family by Adobe have excellent coverage but may not be available at the time of rendering. This can be a concern if you distribute the SVG files on the Internet.
In addition to system fonts, you can also provide fonts that are not
necessarily installed on the system (i.e., fonts that live in user
space). The main reason to do this is to generate reproducible SVG
files as different platforms can have different versions of a font and
thus produce different text metrics. The user_fonts
arguments takes
either paths to font files, fonts from the fontquiver
package, or a
list that specifies the alias. Whereas system_fonts
gets a named
list of families as argument, user_fonts
takes a named tree of lists
of families (sans
, serif
, mono
and symbol
) and faces (plain
,
italic
, bold
, bolditalic
, symbol
):
# Using ttf files from fontquiver here, but it could be any ttf some_file <- fontquiver::font("Liberation", "Sans", "Regular")$ttf other_file <- fontquiver::font("Liberation", "Sans", "Italic")$ttf serif_file <- fontquiver::font("Liberation", "serif", "Italic")$ttf # The outer named list contains families while the inner named list # contains faces: fonts <- list( sans = list( plain = some_file, italic = other_file ), serif = list(plain = serif_file) ) ss <- svglite("plot.svg", user_fonts = fonts) plot.new() text(0.5, 0.5, "Sans Plain text") text(0.2, 0.2, "Sans Italic text", font = 3) text(0.8, 0.8, "Serif text", family = "serif") dev.off()
You can also control which font gets written in the font-family
fields of SVGs by supplying a list containing alias
and file
elements:
file_with_alias <- list(alias = "Foobar Font", file = other_file) fonts <- list(sans = list(plain = file_with_alias)) ss <- svgstring(user_fonts = fonts) plot(1:10) text(0.5, 0.5, "Sans text") dev.off() ss()
fontquiver
fonts are particularly useful for creating reproducible
SVG files. The vdiffr
package uses svglite with fontquiver fonts to
create visual unit tests reliably across platforms. The Liberation
fontset is appropriate for this usage because it features all 12
combinations of standard R families and faces. In addition fontquiver
provides Symbola for the symbol font. The function
fontquiver::font_families()
produces a list with the appropriate
structure and can be directly supplied to svglite:
fonts <- fontquiver::font_families("Liberation") fonts$symbol$symbol <- fontquiver::font_symbol("Symbola") str(fonts, 2) svglite("reproducible.svg", user_fonts = fonts) plot(1:10) dev.off()
The systemfonts package is used to match font family names to fonts installed on
the system. systemfonts will always return a valid font, but if the requested
font is badly misspelled or missing, a default will be returned. To test if the
expected font is matched you can use the match_font()
and font_info()
functions from systemfonts:
systemfonts::match_font("Helvetica") systemfonts::font_info("Helvetica", bold = TRUE)
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