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5.3 Encoding files

The encoding of a font specifies the mapping from character codes (an integer, typically between zero and 255) to the characters themselves; e.g., does a character with code 92 wind up printing as a backslash (as it does under the ASCII encoding) or as a double left quote (as it does under the most common TeX font encoding)? Put another way, the encoding is the arrangement of the characters in the font.

It is sad but true that no single encoding has been widely adopted, even for basic text fonts. (Text fonts and, say, math fonts or symbol fonts will clearly have different encodings.) Every typesetting program and/or font source seems to come up with a new encoding; GNU is no exception (see below). Therefore, when you decide on the encoding for the fonts you create, you should choose whatever is most convenient for the typesetting programs you intend to run it with. (Decent typesetting systems would make it trivial to set font encodings; unfortunately, almost nothing is decent in that regard!)

The encoding file format we invented is a font-format-independent representation of an encoding. Encoding files are "data files" which have the basic syntax elements described above (see section 5.2 Common file syntax). They are usually named with the extension .enc.

The first nonblank non-comment line in an encoding file is a string to put into TFM files as the "coding scheme" to describe the encoding; some common coding schemes are `TeX text', `TeX math symbol', `Adobe standard'. Case is irrelevant; that is, any programs which use the coding scheme should pay no attention to its case.

Thereafter, each nonblank non-comment line defines the character for the corresponding code: the first such line defines the character with code zero, the next with code one, and so on.

Each character consists of a name, optionally followed by ligature information. (All fonts using the same encoding should have the same ligatures, it seems to us.)

5.3.1 Character names  How to write character names.
5.3.2 Ligature definitions  How to define ligatures.
5.3.3 GNU encodings  Why we invented new encodings for GNU.

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