Glyph Bitmap Distribution Format: Difference between revisions

Revision as of 04:48, 31 January 2012

Revision as of 23:52, 17 February 2013

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The '''Glyph Bitmap Distribution Format''' (BDF) by [[Adobe Systems|Adobe]] is a file format for storing [[bitmap font]]s. The content istakes presentedthe asform of a text file that is intended to be human- and computer -readable. BDF is typically used in [[Unix]] environments.

==Overview==

The{{As of | 2013}} the current version of BDF is 2.2. No future revisions are anticipated. Earlier versions were referred to as the Character Bitmap Distribution Format.

The [[X Window]] Consortium adopted BDF 2.1 as a standard for X Window screen fonts, but ishas nowstarted moving towards other standards.

Version 2.2 added support for non-Western writing. For example, [[glyph]]s in a BDF 2.2 font definition can specify rendering from top-to-bottom rather than simply left-to-right.

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Lines beginning with the word "COMMENT" can be inserted within a BDF file. Anything following the "COMMENT" keyword on a line is ignored.

Following the above global declarations, the following entries aremay repeatedrepeat for each glyph.

"STARTCHAR U+0041" specifies the start of a character in version 2.1 and earlier, or of a glyph in version 2.2. The string name of this particular character is "U+0041", whichexpressing isin the [[Unicode]] convention for the code point hexadecimal 41 (decimal 65, the ASCII character "A"). In version 2.1 and earlier, the character name string was limited to 14 characters. In version 2.2, the glyph name string can contain up to 65,535 characters.

"ENCODING 65" declares the decimal code point for this glyph in the font.

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==Version 2.2 Extensions==

Version 2.2 of the BDF specification adds support for non-Western fonts. These additions allow moving the origin by a positive or negative movement on the X and Y axes. This not only accommodates right-to-left writing direction, but even top-to-bottom (for example, for Chinese). The following values provide multinational -font support:

METRICSET: set to 0 for writing direction 0, 1 for writing direction 1, or 2 (in the initial global area) for both writing directions within the same font. Traditional Western left-to-right scripts use "METRICSET 0".

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VVECTOR defines an X-axis offset and a Y-axis offset to transition from a mode 0 glyph to a mode 1 glyph. An opposite offset is applied during a mode 1 to mode 0 glyph transition.

This scheme easily accommodates two writing directions. Historically, fonts had 128 or 256 code points. Today, Unicode allows for over one million code points. Fonts can conceivably contain thousands of glyphs, some of which should be written left-to-right, some right-to-left, and some top-to-bottom. Such manymulti-directiondirectional writing requires creative use of DWIDTH1 and SWIDTH1 for each glyph.

In addition to keywords added for international support, version 2.2 adds the "CONTENTVERSION" declaration. This keyword is followed by an integer to indicate the version number of the font.

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==References==

{{refbegin}}

* {{cite book|others= The [[Unicode Consortium]] |title= The Unicode Standard, Version 5.0 |origyear= |url= |format= |accessdate= 2008-01-13 |edition= 5th edition |series= |volume= |year= 2006 |month= October |publisher= [[Addison-Wesley]] |___location= |isbn= 978-0-321-48091-0 |oclc= |doi= |id= |pages= |chapter= |chapterurl= |quote= |ref= }}

{{refend}}

==External links==

* [http://partners.adobe.com/public/developer/en/font/5005.BDF_Spec.pdf Adobe Glyph Bitmap Distribution Format (BDF) Specification, version 2.2]<!-- application/pdf, 101 kbytes -->

[[Category:Font formats]]