A fallback

font In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a " sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design. In mo ...

is a reserve typeface containing symbols for as many

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...

characters as possible. When a display system encounters a character that is not part of the repertoire of any of the other available fonts, a symbol from a fallback font is used instead. Typically, a fallback font will contain symbols representative of the various types of Unicode characters. Systems that do not offer a fallback font typically display black or white rectangles,

question mark The question mark (also known as interrogation point, query, or eroteme in journalism) is a punctuation mark that indicates an interrogative clause or phrase in many languages. History In the fifth century, Syriac Bible manuscripts used ...

s, the Unicode Replacement Character (U+FFFD), or nothing at all, in place of missing characters. Placing one or more fallback fonts at the end of a list of preferred fonts ensures that there are no missing characters.

Unicode BMP Fallback font

0 0
2 0

The Unicode BMP Fallback font is a Unicode font that was originally created for

debugging In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve i ...

purposes. It contains a

glyph A glyph () is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A g ...

for every character in the Unicode

Basic Multilingual Plane In the Unicode standard, a plane is a continuous group of 65,536 (216) code points. There are 17 planes, identified by the numbers 0 to 16, which corresponds with the possible values 00–1016 of the first two positions in six position hexadeci ...

. Each glyph consists of a box containing the four hexadecimal digits corresponding to the Unicode value. The example to the left is a mock-up of the glyph for a

space character In computer programming, whitespace is any character or series of characters that represent horizontal or vertical space in typography. When rendered, a whitespace character does not correspond to a visible mark, but typically does occupy an area ...

(U+0020). Unlike the Unicode Last Resort font, the Unicode BMP Fallback font displays a different glyph for each different Unicode character, but cannot display all Unicode characters. Because four hexadecimal digits can only represent 64K characters (0000=0, FFFF=65,535) the Unicode BMP Fallback is limited to the 64K characters in the Unicode Basic Multilingual Plane.

Unicode Last Resort font

As of Unicode version 5.0, the Unicode consortium provides a fallback font to represent types of Unicode characters. This is a version of the

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...

Last Resort system font, modified to work on non-Apple platforms and made available by Apple via the Unicode Consortium. The font is released as an open-sourced font under

SIL Open Font License The SIL Open Font License (or OFL in short) is one of the major open font licenses, which allows embedding, or "bundling", of the font in commercially sold products. OFL is a free and open source license. It was created by SIL Internationa ...

in Unicode Version 14.0 (2021). The symbols provided by the Unicode Last Resort font place glyphs into categories based on their location in the

system and provide a hint to the user about which font or script is required to view the unavailable characters. The symbols provided by the Unicode Last Resort font are square with rounded corners with a bold outline. In the left and right sides of the outline, the

range that the character belongs to is given using hexadecimal digits. Top and bottom are used for one or two descriptions of the

Unicode block A Unicode block is one of several contiguous ranges of numeric character codes ( code points) of the Unicode character set that are defined by the Unicode Consortium for administrative and documentation purposes. Typically, proposals such as the ...

. A symbol representative of the block is centered inside the square. Unlike the Unicode BMP Fallback font or the GNU Unifont, the Unicode Last Resort font displays the same glyph for many different Unicode characters. Using this one-glyph-per-block generalization allows the Unicode Last Resort font to contain a glyph for every character in Unicode despite the fact that the total number of Unicode characters exceeds the address space of an sfnt (TrueType and OpenType) font structure, which has a 16-bit glyph index that can store a maximum of 65,536 glyphs. Unicode now has over 100,000 defined characters, with a potential address space of over one million characters—over 15 times the sfnt size limit. Unicode Last Resort Font will therefore not break as Unicode continues to grow and the

(BMP) and surrogate planes fill up further.

Apple's Last Resort font

Apple's Last Resort font is a system font for the

Macintosh operating systems Two major famlies of Mac operating systems were developed by Apple Inc. In 1984, Apple debuted the operating system that is now known as the "Classic" Mac OS with its release of the original Macintosh System Software. The system, rebranded "M ...

that is identical to the Unicode Last Resort font (which was created for the Unicode consortium by Apple). Apple's Last Resort font was first included in Mac OS 8.5 in 1998, for the benefit of applications using

Apple Type Services for Unicode Imaging The Apple Type Services for Unicode Imaging (ATSUI) is the set of services for rendering Unicode-encoded text introduced in Mac OS 8.5 and carried forward into Mac OS X. It replaced the WorldScript engine for legacy encodings. Obsolescence ...

(ATSUI). It is also used in

. In 2001, for Mac OS X 10.1 the Last Resort font design was revised to include the border text and was re-digitized, and extended by

Michael Everson Michael Everson (born January 9, 1963) is an American and Irish linguist, script encoder, typesetter, type designer and publisher. He runs a publishing company called Evertype, through which he has published over a hundred books since 2006. H ...

Evertype Michael Everson (born January 9, 1963) is an American and Irish linguist, script encoder, typesetter, type designer and publisher. He runs a publishing company called Evertype, through which he has published over a hundred books since 2006. Hi ...

, who continues to update it with each new release of Unicode.

GNU Unifont

The

GNU Unifont GNU Unifont is a free Unicode bitmap font using an intermediate bitmapped font format created by Roman Czyborra. The main Unifont covers all of the Basic Multilingual Plane (BMP). The "upper" companion covers significant parts of the Supplemen ...

is a font that contains a glyph for every character in the Unicode

Basic multilingual plane In the Unicode standard, a plane is a continuous group of 65,536 (216) code points. There are 17 planes, identified by the numbers 0 to 16, which corresponds with the possible values 00–1016 of the first two positions in six position hexadeci ...

. Unlike with the Unicode BMP Fallback font or the Unicode Last Resort Font, the characters in GNU Unifont are low resolution

bitmap In computing, a bitmap is a mapping from some domain (for example, a range of integers) to bits. It is also called a bit array or bitmap index. As a noun, the term "bitmap" is very often used to refer to a particular bitmapping application: t ...

approximations of each glyph, which results in character renderings which are of low quality but adequate to be a distinguishable graphical representation of a given code point. The goal of the GNU Unifont project is to "lower our expectations about the font quality to a reasonable degree" in order to obtain complete coverage of all Unicode characters. To achieve this goal, all glyphs are 16 pixels in height and either 8 or 16 pixels in width. A TrueType version of the GNU Unifont is available for free.

References

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