Glyph Bitmap Distribution Format: Difference between revisions

Revision as of 19:37, 21 January 2008

Revision as of 03:19, 15 February 2008

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defines a character as composed of one or more glyphs. Therefore the glyph is a more basic typographic element than the character.

The [[X-Windows Window]] Consortium adopted BDF 2.1 as a standard for X-Windows Window screen fonts, but is now moving towards other standards.

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

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"FONT -gnu-unifont-medium-r-normal--16-160-75-75-c-80-iso10646-1" defines the font family and face names.

"SIZE 16 75 75" defines this to be a 16 point font, with an X-axis resolution of 75 dots per inch (dpi) and a Y-axis resolution of 75 dpi. This is the norm under X-Windows Window.

"FONTBOUNDINGBOX 16 16 0 -2" defines a bounding box for the font of 16 pixels wide by 16 pixels high, with the lower left-hand corner starting at x=0, y=-2. Note that although the bounding box is defined to be a 16 by 16 cell, this can be overridden for individual glyphs. The "A" glyph, for example, is only 8 pixels wide.

"STARTPROPERTIES 2" declares that two special properties will follow. "STARTPROPERTIES" is optional in the BDF specification. X-Windows Window allows the properties FONT_ASCENT and FONT_DESCENT to show the height above and below the baseline, respectively, for all glyphs. "FONT_ASCENT 14" declares that 14 of the 16 pixels in height are above the baseline. "FONT_DESCENT 2" declares that 2 of the 16 pixels in height are below the baseline. "ENDPROPERTIES" appears at the end of the "STARTPROPERTIES" section.

"CHARS 1" declares that one character will follow. Although Adobe now refers to this file format as the Glyph BDF, they have retained the keyword "CHARS" in the final version of the specification.

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For more detailed information, consult the version 2.2 specification.

==X-Windows Window Properties==

X-Windows Window font utilities (for example, the xlfd command under Linux) support several properties that can be specified in the STARTPROPERTIES section of a BDF file. A generic BDF file is in ASCII encoding. X-Windows Window properties are specified using ISO 8859-1 encoding, which is an extension of ASCII. These properties include:

* CAP_HEIGHT int32 -- the height above the baseline of a capital letter.

* COPYRIGHT string -- a copyright statement.

* DEFAULT_CHAR card32 -- the default character (glyph) to display for an undefined glyph.

* FACE_NAME string -- the name of the face for this font.

* FONT string -- the X-Windows Window name of the font.

* FONT_ASCENT int32 -- the height above the baseline, for line spacing calculation.

* FONT_DESCENT int32 -- the descent below the baseline, for line spacing calculation.