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.TH FONT 6
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.SH NAME
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font, subfont \- external format for fonts and subfonts
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.SH SYNOPSIS
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.B #include <draw.h>
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.SH DESCRIPTION
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Fonts and subfonts are described in
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.IR cachechars (2).
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.PP
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External fonts are described by a plain text file that can be read using
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.IR openfont .
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The format of the file is a header followed by any number of
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subfont range specifications.
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The header contains two numbers: the height and the ascent, both in pixels.
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The height is the inter-line spacing and the ascent is the distance
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from the top of the line to the baseline. These numbers are chosen
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to display consistently all the subfonts of the font.
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A subfont range specification contains two or three numbers and a file name.
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The numbers are the inclusive range of characters covered by the subfont,
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with an optional starting position within the subfont,
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and the file name names an external file suitable for
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.I readsubfont
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(see
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.IR graphics (2)).
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The minimum number of a covered range is mapped to the specified starting position
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(default zero) of the
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corresponding subfont.
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If the subfont file name does not begin with a slash, it is taken relative to the
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directory containing the font file.
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Each field must be followed by some white space.
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Each numeric field may be C-format decimal, octal, or hexadecimal.
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.PP
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External subfonts are represented in a more rigid format
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that can be read and written using
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.I readsubfont
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and
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.I writesubfont
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(see
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.IR subfont (2)).
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The format for subfont files is: an image containing character glyphs,
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followed by a subfont header, followed by character information.
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The image has the format for external image files described in
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.IR image (6).
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The subfont header has 3
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decimal strings:
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.BR n ,
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.BR height ,
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and
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.BR ascent .
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Each number is right-justified and blank padded in 11 characters, followed by a blank.
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The character
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.B info
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consists of
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.BR n +1
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6-byte entries, each giving the
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.B Fontchar
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.B x
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(2 bytes, low order byte first),
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.BR top ,
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.BR bottom ,
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.BR left ,
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and
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.BR width .
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The
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.B x
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field of the last
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.B Fontchar
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is used to calculate the image width
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of the previous character; the other fields in the last
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.B Fontchar
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are irrelevant.
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.PP
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Note that the convention of using the character with value zero (NUL) to represent
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characters of zero width (see
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.IR draw (2))
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means that fonts should have, as their zeroth character,
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one with non-zero width.
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.SH FILES
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.TF /lib/font/bit/*
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.TP
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.B /lib/font/bit/*
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font directories
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.SH "SEE ALSO"
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.IR graphics (2),
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.IR draw (2),
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.IR cachechars (2),
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.IR subfont (2)
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