Hershey Vector Fonts in R

Description

If the vfont argument to one of the text-drawing functions (text, mtext, title, axis, and contour) is a character vector of length 2, Hershey vector fonts are used to render the text.

These fonts have two advantages:

1. vector fonts describe each character in terms of a set of points; R renders the character by joining up the points with straight lines. This intimate knowledge of the outline of each character means that R can arbitrarily transform the characters, which can mean that the vector fonts look better for rotated and 3d text.
2. this implementation was adapted from the GNU libplot library which provides support for non-ASCII and non-English fonts. This means that it is possible, for example, to produce weird plotting symbols and Japanese characters.

Drawback:
You cannot use mathematical expressions (plotmath) with Hershey fonts.

Usage

Hershey

Details

The Hershey characters are organised into a set of fonts, which are specified by a typeface (e.g., serif or sans serif) and a fontindex or “style” (e.g., plain or italic). The first element of vfont specifies the typeface and the second element specifies the fontindex. The first table produced by demo(Hershey) shows the character a produced by each of the different fonts.

The available typeface and fontindex values are available as list components of the variable Hershey. The allowed pairs for (typeface, fontindex) are:

and the indices of these are available as Hershey$allowed.

Escape sequences:

The string to be drawn can include escape sequences, which all begin with a \. When R encounters a \, rather than drawing the \, it treats the subsequent character(s) as a coded description of what to draw.

One useful escape sequence (in the current context) is of the form: \123. The three digits following the \ specify an octal code for a character. For example, the octal code for p is 160 so the strings "p" and "\160" are equivalent. This is useful for producing characters when there is not an appropriate key on your keyboard.

The other useful escape sequences all begin with \\. These are described below. Remember that backslashes have to be doubled in R character strings, so they need to be entered with four backslashes.

Symbols:

an entire string of Greek symbols can be produced by selecting the Serif Symbol or Sans Serif Symbol typeface. To allow Greek symbols to be embedded in a string which uses a non-symbol typeface, there are a set of symbol escape sequences of the form \\ab. For example, the escape sequence \\*a produces a Greek alpha. The second table in demo(Hershey) shows all of the symbol escape sequences and the symbols that they produce.

ISO Latin-1:

further escape sequences of the form \\ab are provided for producing ISO Latin-1 characters (for example, if you only have a US keyboard). Another option is to use the appropriate octal code. The (non-ASCII) ISO Latin-1 characters are in the range 241...377. For example, \366 produces the character o with an umlaut. The third table in demo(Hershey) shows all of the ISO Latin-1 escape sequences.

Special Characters:

a set of characters are provided which do not fall into any standard font. These can only be accessed by escape sequence. For example, \\LI produces the zodiac sign for Libra, and \\JU produces the astronomical sign for Jupiter. The fourth table in demo(Hershey) shows all of the special character escape sequences.

Cyrillic Characters:

cyrillic characters are implemented according to the K018-R encoding. On a US keyboard, these can be produced using the Serif typeface and Cyrillic (or Oblique Cyrillic) fontindex and specifying an octal code in the range 300 to 337 for lower case characters or 340 to 377 for upper case characters. The fifth table in demo(Hershey) shows the octal codes for the available cyrillic characters.

Japanese Characters:

83 Hiragana, 86 Katakana, and 603 Kanji characters are implemented according to the EUC (Extended Unix Code) encoding. Each character is identified by a unique hexadecimal code. The Hiragana characters are in the range 0x2421 to 0x2473, Katakana are in the range 0x2521 to 0x2576, and Kanji are (scattered about) in the range 0x3021 to 0x6d55.

When using the Serif typeface and EUC fontindex, these characters can be produced by a pair of octal codes. Given the hexadecimal code (e.g., 0x2421), take the first two digits and add 0x80 and do the same to the second two digits (e.g., 0x21 and 0x24 become 0xa4 and 0xa1), then convert both to octal (e.g., 0xa4 and 0xa1 become 244 and 241). For example, the first Hiragana character is produced by \244\241.

It is also possible to use the hexadecimal code directly. This works for all non-EUC fonts by specifying an escape sequence of the form \\#J1234. For example, the first Hiragana character is produced by \\#J2421.

The Kanji characters may be specified in a third way, using the so-called "Nelson Index", by specifying an escape sequence of the form \\#N1234. For example, the Kanji for “one” is produced by \\#N0001.

demo(Japanese) shows the available Japanese characters.

Raw Hershey Glyphs:

all of the characters in the Hershey fonts are stored in a large array. Some characters are not accessible in any of the Hershey fonts. These characters can only be accessed via an escape sequence of the form \\#H1234. For example, the fleur-de-lys is produced by \\#H0746. The sixth and seventh tables of demo(Hershey) shows all of the available raw glyphs.

References

http://www.gnu.org/software/plotutils/plotutils.html

See Also

demo(Hershey), text, contour.

Japanese for the Japanese characters in the Hershey fonts.

Examples

Hershey

## for tables of examples, see demo(Hershey)