A fallback

font In metal typesetting, a font is a particular size, weight and style of a ''typeface'', defined as the set of fonts that share an overall design. For instance, the typeface Bauer Bodoni (shown in the figure) includes fonts " Roman" (or "regul ...

is a reserve typeface containing symbols for as many

Unicode Unicode or ''The Unicode Standard'' or TUS is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 16.0 defines 154,998 Char ...

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. This should not be confused with a

Unicode font A Unicode font is a computer font that maps glyphs to code points defined in the Unicode Standard. The vast majority of modern computer fonts use Unicode mappings, even those fonts which only include glyphs for a single writing system, or even onl ...

, which contains a large number of glyphs that actually contain the existing Unicode characters themselves for a large number of characters, such as

GNU Unifont GNU Unifont is a free Unicode bitmap font created by Roman Czyborra. The main Unifont covers all of the Basic Multilingual Plane (BMP). The "upper" companion covers significant parts of the Supplementary Multilingual Plane (SMP). The "Unifont J ...

. 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, punctuation mark that indicates a question or interrogative clause or phrase in many languages. History The history of the question mark is ...

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

that was originally created for

debugging In engineering, debugging is the process of finding the Root cause analysis, root cause, workarounds, and possible fixes for bug (engineering), bugs. For software, debugging tactics can involve interactive debugging, control flow analysis, Logf ...

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 ...

for every character in the Unicode

Basic Multilingual Plane In the Unicode standard, a plane is a contiguous 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 hexadecimal ...

. 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 A whitespace character is a character data element that represents white space when text is rendered for display by a computer. For example, a ''space'' character (, ASCII 32) represents blank space such as a word divider in a Western scri ...

(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 65K characters (0000=0, FFFF=65,535) the Unicode BMP Fallback is limited to the 65K 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, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

Last Resort system font, modified to work on non-Apple platforms and made available by Apple via the Unicode Consortium. 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 Mac operating systems were developed by Apple Inc. in a succession of two major series. In 1984, Apple debuted the operating system that is now known as the classic Mac OS with its release of the System 1, original Macintosh System Software. Th ...

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 macOS, previously OS X and originally Mac OS X, is ...

(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 1963) is an American and Irish linguistics, linguist, Character encoding, script encoder, typesetting, typesetter, type designer and Publishing, publisher. He runs a publishing company called Evertype, through which ...

Evertype Michael Everson (born January 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 one hundred books since 2006. His ...

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

Unicode Consortium versions

Since version 13.000, the font family is released 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 Global, the ...

1.1. The family includes Last Resort, Last Resort High-Efficiency. Last Resort High-Efficiency uses Format 13 (Many-to-one range mappings) 'cmap' (character to glyph index mapping) table, which reduces the size of the font, but may not be compatible with some environments.

Releases

Source:Releases
/ref> *13.000 (2020-10-08): Supports Unicode Version 13.0.0. Only Format 13 cmap table is included. *13.001 (2020-10-22): Added Last Resort High-Efficiency. Both fonts include Format 4 cmap table, with Last Resort includes Format 12 cmap table and LRHE includes Format 13 cmap table. *14.000 (2021-12-01): Supports Unicode Version 14.0.0. Added 12 glyphs for 12 new blocks. Modified 2 glyphs in 2 existing blocks (Ahom, Tangut Supplement). *15.000 (2022-09-13): Supports Unicode Version 15.0.0. 'meta' table was removed. Added 7 glyphs for 7 new blocks. Modified 6 glyphs in 6 existing blocks (Egyptian Hieroglyph Format Controls, Number Forms, Mathematical Operators Supplement, Variation Selectors, CJK Unified Ideographs Extension F, Variation Selectors Supplement). *15.100 (2023-09-11): Supports Unicode Version 15.1.0. Added one new glyph that corresponds to the newly added CJK Unified Ideographs Extension I block; 627 mappings that correspond to the 627 new characters in Unicode Version 15.1 were changed. *16.000 (2024-09-10): Supports Unicode Version 16.0.0. Added 10 new glyphs for 10 new blocks. 5,185 mappings were changed.

References

{{Reflist

External links

Brief discussion of Last Resort by Michael Everson

Unicode Character Stories by Peter Constable

at Unicode.org
Unicode BMP Fallback Font
at SIL.org Unicode typefaces