Fallback font
Encyclopedia
A fallback font
is a reserve typeface containing symbols for as many Unicode
characters as possible. When a display system encounters a character which 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
s, or nothing at all in place of missing characters. Placing one or more fallback fonts at the end of a list of preferred fonts insures that there are no missing characters.
Typeface
In typography, a typeface is the artistic representation or interpretation of characters; it is the way the type looks. Each type is designed and there are thousands of different typefaces in existence, with new ones being developed constantly....
is a reserve typeface containing symbols for as many Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
characters as possible. When a display system encounters a character which 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
Question mark
The question mark , is a punctuation mark that replaces the full stop at the end of an interrogative sentence in English and many other languages. The question mark is not used for indirect questions...
s, or nothing at all in place of missing characters. Placing one or more fallback fonts at the end of a list of preferred fonts insures that there are no missing characters.
The Unicode BMP Fallback font
2 0The Unicode BMP Fallback font is a Unicode font that was originally created for debugging
Debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...
purposes. It contains a glyph for every character in the Unicode Basic multilingual plane. 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 (
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.
The Unicode Last Resort Font
This is a version of the Mac OS X 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 Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
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 Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
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
Unicode block
In Unicode, a block is defined as one contiguous range of code points. Blocks are named uniquely and have no overlap. They may be defined with the starting and ending code points. The block explicitly can include code points that are unassigned and non-characters. Code points not belonging to any...
. A symbol
representative of the block is centered inside the square.
Unlike the Unicode BMP Fallback font or the 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
Sfnt
Sfnt is a font file format used for PostScript, TrueType and OpenType fonts. Sfnt stands for spline font, and was originally developed for Apple Computer's QuickDraw....
(TrueType and OpenType) font structure, which has a 16-bit glyph index that can store a maximum of 65,536 glyphs. Unicode has now 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 Basic Multilingual Plane (BMP) and surrogate planes fill up further.
The GNU Unifont
The GNU Unifont is a font that contains a glyph for every character in the Unicode Basic multilingual plane. Unlike the Unicode BMP Fallback font or the Unicode Last Resort Font, the characters are readable by a human - an "A" looks like an "A" instead of a generic glyph or a hexadecimal code.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.
Apple's Last Resort Font
Apple's Last Resort Font is a Mac OSMac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
system font 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
Mac OS
Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
8.5 in 1998, for the benefit of applications using Apple Type Services for Unicode Imaging
Apple Type Services for Unicode Imaging
The Apple Type Services for Unicode Imaging is the set of services for rendering Unicode-encoded text starting with Mac OS 8.5 and in Mac OS X.It replaced the WorldScript engine for legacy encodings....
(ATSUI). It is also used in Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
. In 2001, for the second release of OS X, the Last Resort font design was revised to include the border text and was re-digitized, and extended by Michael Everson
Michael Everson
Michael Everson is a linguist, script encoder, typesetter, and font designer. His central area of expertise is with writing systems of the world, specifically in the representation of these systems in formats for computer and digital media...
of Evertype, who continues to update it with each new release of Unicode.
See also
- Unicode typeface
- Free software Unicode typefacesFree software Unicode typefacesA few projects exist to provide free and open-source Unicode typefaces, i.e. Unicode typefaces which are open-source and designed to contain glyphs of all Unicode characters. However there are also numerous projects aimed at providing only a certain script, such as the Arabeyes Arabic font...
- GNU UnifontGNU UnifontThe GNU Unifont by Roman Czyborra is a free bitmap font that covers the Unicode Basic Multilingual Plane , using an intermediate bitmapped font format....
- UnicodeUnicodeUnicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
- Fonts on Macintosh