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tfont.7 (5393B)
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1 .TH FONT 7
2 .SH NAME
3 font, subfont \- external format for fonts and subfonts
4 .SH SYNOPSIS
5 .B #include <draw.h>
6 .SH DESCRIPTION
7 Fonts and subfonts are described in
8 .MR cachechars (3) .
9 .PP
10 External bitmap fonts are described by a plain text file that can be read using
11 .IR openfont .
12 The format of the file is a header followed by any number of
13 subfont range specifications.
14 The header contains two numbers: the height and the ascent, both in pixels.
15 The height is the inter-line spacing and the ascent is the distance
16 from the top of the line to the baseline. These numbers are chosen
17 to display consistently all the subfonts of the font.
18 A subfont range specification contains two or three numbers and a file name.
19 The numbers are the inclusive range of characters covered by the subfont,
20 with an optional starting position within the subfont,
21 and the file name names an external file suitable for
22 .I readsubfont
23 (see
24 .MR graphics (3) ).
25 The minimum number of a covered range is mapped to the specified starting position
26 (default zero) of the
27 corresponding subfont.
28 If the subfont file name does not begin with a slash, it is taken relative to the
29 directory containing the font file.
30 Each field must be followed by some white space.
31 Each numeric field may be C-format decimal, octal, or hexadecimal.
32 .PP
33 External subfonts are represented in a more rigid format
34 that can be read and written using
35 .I readsubfont
36 and
37 .I writesubfont
38 (see
39 .MR subfont (3) ).
40 The format for subfont files is: an image containing character glyphs,
41 followed by a subfont header, followed by character information.
42 The image has the format for external image files described in
43 .MR image (7) .
44 The subfont header has 3
45 decimal strings:
46 .BR n ,
47 .BR height ,
48 and
49 .BR ascent .
50 Each number is right-justified and blank padded in 11 characters, followed by a blank.
51 The character
52 .B info
53 consists of
54 .BR n +1
55 6-byte entries, each giving the
56 .B Fontchar
57 .B x
58 (2 bytes, low order byte first),
59 .BR top ,
60 .BR bottom ,
61 .BR left ,
62 and
63 .BR width .
64 The
65 .B x
66 field of the last
67 .B Fontchar
68 is used to calculate the image width
69 of the previous character; the other fields in the last
70 .B Fontchar
71 are irrelevant.
72 .PP
73 Note that the convention of using the character with value zero (NUL) to represent
74 characters of zero width (see
75 .MR draw (3) )
76 means that fonts should have, as their zeroth character,
77 one with non-zero width.
78 .SS "Font Names
79 .PP
80 Font names in Plan 9 from User Space are
81 a small language describing a font.
82 The most basic form is the name of an existing bitmap font file,
83 following the convention:
84 .IP
85 .B /lib/font/bit/\fIname\fP/\fIrange\fP.\fIsize\fP.font
86 .PD
87 .PP
88 where
89 .I size
90 is approximately the height in pixels of the lower case letters
91 (without ascenders or descenders).
92 .I Range
93 gives some indication of which characters will be available: for example
94 .BR ascii ,
95 .BR latin1 ,
96 .BR euro ,
97 or
98 .BR unicode .
99 .B Euro
100 includes most European languages, punctuation marks, the International Phonetic
101 Alphabet, etc., but no Oriental languages.
102 .B Unicode
103 includes every character for which appropriate-sized images exist on the system.
104 .PP
105 In Plan 9 from User Space, the font files are rooted in
106 .B $PLAN9/font
107 instead of
108 .BR /lib/font/bit ,
109 but to keep old references working, paths beginning with
110 .B /lib/font/bit
111 are interpreted as references to the actual font directory.
112 .PP
113 Fonts need not be stored on disk in the Plan 9 format.
114 If the font name has the form
115 .BR /mnt/font/\fIname\fP/\fIsize\fP/font ,
116 .I fontsrv
117 is invoked to synthesize a bitmap font from the operating system's installed vector fonts.
118 The command
119 .B fontsrv
120 .B -p
121 .B .
122 lists the available fonts.
123 See
124 .MR fontsrv (4)
125 for more.
126 .PP
127 If the font name has the form
128 .BR \fIscale\fP*\fIfontname\fP ,
129 where
130 .I scale
131 is a small decimal integer, the
132 .I fontname
133 is loaded and then scaled by pixel repetition.
134 .PP
135 The Plan 9 bitmap fonts were designed for screens with pixel density around 100 DPI.
136 When used on screens with pixel density above 200 DPI,
137 the bitmap fonts are automatically pixel doubled.
138 Similarly, fonts loaded from
139 .MR fontsrv (4)
140 are automatically doubled in size by varying the effective
141 .I size
142 path element.
143 In both cases, the effect is that a single font name
144 can be used on both low- and high-density displays (or even in a window moved between differing displays)
145 while keeping roughly the same effective size.
146 .PP
147 For more control over the fonts used on low- and high-density displays,
148 if the font name has the form
149 .BR \fIlowfont\fP,\fIhighfont\fP ,
150 .I lowfont
151 is used on low-density displays and
152 .I highfont
153 on high-density displays.
154 In effect, the behavior described above is that the font name
155 .IP
156 .B /lib/font/bit/lucsans/euro.8.font
157 .PD
158 .PP
159 really means
160 .IP
161 .B /lib/font/bit/lucsans/euro.8.font,2*/lib/font/bit/lucsans/euro.8.font
162 .PD
163 .PP
164 and similarly
165 .IP
166 .B /mnt/font/LucidaGrande/15a/font
167 .PD
168 .PP
169 really means
170 .IP
171 .B /mnt/font/LucidaGrande/15a/font,/mnt/font/LucidaGrande/30a/font
172 .PD
173 .PP
174 Using an explicit comma-separated font pair allows finer control, such as
175 using a Plan 9 bitmap font on low-density displays but switching to
176 a system-installed vector font on high-density displays:
177 .IP
178 .B /lib/font/bit/lucsans/euro.8.font,/mnt/font/LucidaGrande/30a/font
179 .PD
180 .PP
181 .SH FILES
182 .TF \*9/font/*
183 .TP
184 .B \*9/font/*
185 font directories
186 .SH "SEE ALSO"
187 .MR graphics (3) ,
188 .MR draw (3) ,
189 .MR cachechars (3) ,
190 .MR subfont (3)