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".
SWIDTH1, DWIDTH1: these have the same parameters as SWIDTH and DWIDTH, respectively. DWIDTH1 must be present for a METRICSET 1 glyph. Its offsets can be positive or negative.
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 many-direction 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.
For more detailed information, consult the version 2.2 specification.
Read more about this topic: Glyph Bitmap Distribution Format
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