1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>Xgridfit</title>
<link rel="stylesheet" href="oeg.css" media="screen" type="text/css" />
<link rel="stylesheet" href="parchment.css" media="screen"
type="text/css" title="parchment" />
<link rel="alternate stylesheet" href="legible.css" media="screen"
type="text/css" title="legible" />
<style type="text/css" media="print"> @import "oeg.print.css"; </style>
<meta name="AUTHOR" content="Peter S. Baker" />
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
<div id="jumplist">
<a href="http://sourceforge.net"><img src="http://sflogo.sourceforge.net/sflogo.php?group_id=159705&type=4" width="125" height="37" border="0" alt="SourceForge.net Logo" /></a>
<a href="http://xgridfit.sourceforge.net/">Home Page</a>
<a href="http://sourceforge.net/projects/xgridfit">Project Page</a>
<a href="http://sourceforge.net/project/showfiles.php?group_id=159705">Download</a>
<a href="http://xgridfit.cvs.sourceforge.net/xgridfit/xgridfit/">CVS repository</a>
</div>
<div id="content">
<h1>Tutorial 2: Gentium's o</h1>
<p>
The o in Gentium Italic presents us with a slightly more complex
task than the period. The glyph shape itself is more complicated,
and the distances we need to regulate are less standardized. Here
is the glyph as it appears in FontForge: we have added names for
the points that will have to be explicitly positioned and
distances (in font units) for the stems that will have to be
regulated.
</p>
<table>
<tr>
<td>
<img src="Gentium_o.png" alt="Gentium period"/>
</td>
</tr>
</table>
<p>
Notice that the distances at the top and bottom of the glyph do
not quite match; the same is true of the left and right. In fact,
all of the lower-case letters with curves somewhat like that of o
(a, c, d, e, g, etc.) have curves of slightly different widths. In
a font of the quality of Gentium, it would be a mistake to assume
that this variation is inadvertent; rather, Victor Gaultney was
presumably aiming for optical rather than mathematical consistency
in his glyph outlines. What is true of the stems is also true of
the sidebearings: the left sidebearings of the lower-case letters
with rounded left sides are slightly different.
</p>
<p>
These minor differences can cause problems at low resolutions,
where a difference of a single pixel can make a character look
lopsided, or too bold, or too thin. At the same time, we want to
preserve the differences at higher resolutions, as on good laser
printers or imagesetters. This is not really a problem for us,
since the <a href="cvt.html#cut-in-expl">control-value cut in</a>
is intended to handle precisely this kind of situation. We need
only to choose a standard width for these curved stems; if we make
sure that the cut-in is always used, our standard width will be
used at low resolutions and the designer's widths at high
resolutions. We can experiment with the standard width and with
various settings for the cut-in at any time.
</p>
<p>
The x-height and the distance of the bottom point of a rounded
lower-case glyph from the baseline are consistent in this font.
We will add the following control values to the ones we defined
for the period:
</p>
<pre>
<control-value name="x-height" value="936"/>
<control-value name="lc-round-char-bottom" value="-41"/>
<control-value name="lc-vert-round-stem" value="143"/>
<control-value name="lc-horz-round-stem" value="115"/>
<control-value name="lc-round-char-left-side" value="55"/>
</pre>
<p>
And we will get ready to write the glyph program by creating the
<glyph> element and defining constants for the key point
numbers:
</p>
<pre>
<glyph ps-name="o">
<constant name="last" value="47"/>
<constant name="topa" value="43"/>
<constant name="topb" value="3"/>
<constant name="bottoma" value="30"/>
<constant name="bottomb" value="13"/>
<constant name="lefta" value="35"/>
<constant name="leftb" value="8"/>
<constant name="righta" value="0"/>
<constant name="rightb" value="20"/>
</glyph>
</pre>
<p>
For the <i>o</i>, we will nest <a
href="moves.html#move"><move></a> elements, building XML
structures to correspond to the visible features of the glyph: the
four rounded stems at the left, right, top and bottom. Remember
that when we nest a <move> inside a <move> element,
the point moved by the parent <move> is implicitly the
reference point for the child <move>. Here are the
horizontal and vertical moves:
</p>
<pre>
<with-vectors axis="x">
<move distance="lc-round-char-left-side">
<reference>
<point num="left-sidebearing"/>
</reference>
<point num="lefta"/>
<move distance="lc-vert-round-stem">
<point num="leftb"/>
</move>
</move>
<move>
<reference>
<point num="lefta"/>
</reference>
<point num="rightb"/>
<move distance="lc-vert-round-stem">
<point num="righta"/>
</move>
</move>
</with-vectors>
<with-vectors axis="y">
<move distance="lc-round-char-bottom">
<point num="bottoma"/>
<move distance="lc-horz-round-stem">
<point num="bottomb"/>
</move>
</move>
<move distance="x-height">
<point num="topa"/>
<move distance="lc-horz-round-stem">
<point num="topb"/>
</move>
</move>
</with-vectors>
<interpolate-untouched-points/>
</pre>
<p>
First we position point <tt>lefta</tt> relative to the
<tt>left-sidebearing</tt> point (defined in the last tutorial as a
global <constant> dependent on point <tt>last</tt>). Then we
position point <tt>leftb</tt> distance <tt>lc-vert-round-stem</tt>
from <tt>lefta</tt>. We do the same with the right side of the
glyph, but this time we start by positioning point <tt>rightb</tt>
relative to point <tt>lefta</tt>, and then we work from the right
side of the stem to the left. By omitting a <tt>distance</tt>
attribute from the outer <move>, we accept, but round, the
design width of the glyph. Later, if we find that one or more
other glyphs in the font are the same width as the <i>o</i>, we
can add a <control-value> for that measurement and a
<tt>distance</tt> attribute here.
</p>
<p>
For the y axis, the operations are similar to what we did on the x
axis. Here, however, we omit the reference points and position
points <bottoma> and <topa> at absolute positions on
the grid. If we go on writing instructions for this font, we will
use the control values <tt>x-height</tt> and
<tt>lc-round-char-bottom</tt> so frequently that it will make
sense to round them in the <pre-program>, saving the
TrueType engine the trouble of rounding them over and over while
executing glyph programs. So we add these lines to the
<pre-program>:
</p>
<pre>
<round value="x-height"/>
<round value="lc-round-char-bottom"/>
</pre>
<p>
And we add attributes <tt>round="no"</tt> and <tt>cut-in="no"</tt>
to the two outer <move> elements. (We don't need the cut-in
with such standard measurements; and for technical reasons it
makes sense to turn off rounding and the cut-in at the same time.)
Now the glyph program for <i>o</i> looks like this:
</p>
<pre>
<glyph ps-name="o">
<constant name="last" value="47"/>
<constant name="topa" value="43"/>
<constant name="topb" value="3"/>
<constant name="bottoma" value="30"/>
<constant name="bottomb" value="13"/>
<constant name="lefta" value="35"/>
<constant name="leftb" value="8"/>
<constant name="righta" value="0"/>
<constant name="rightb" value="20"/>
<with-vectors axis="x">
<move distance="lc-round-char-left-side">
<reference>
<point num="left-sidebearing"/>
</reference>
<point num="lefta"/>
<move distance="lc-vert-round-stem">
<point num="leftb"/>
</move>
</move>
<move>
<reference>
<point num="lefta"/>
</reference>
<point num="rightb"/>
<move distance="lc-vert-round-stem">
<point num="righta"/>
</move>
</move>
</with-vectors>
<with-vectors axis="y">
<move distance="lc-round-char-bottom" round="no" cut-in="no">
<point num="bottoma"/>
<move distance="lc-horz-round-stem">
<point num="bottomb"/>
</move>
</move>
<move distance="x-height" round="no" cut-in="no">
<point num="topa"/>
<move distance="lc-horz-round-stem">
<point num="topb"/>
</move>
</move>
</with-vectors>
<interpolate-untouched-points/>
</glyph>
</pre>
<p>
And now the <pre-program>, which we began to construct in
the last tutorial, looks like this:
</p>
<pre>
<pre-program>
<round value="period-height"/>
<round value="x-height"/>
<round value="lc-round-char-bottom"/>
<control-value-delta>
<delta-set size="11" distance="-8" cv="period-height"/>
</control-value-delta>
</pre-program>
</pre>
<p>
At 20 pixels per em, the grid-fitted glyph now looks like this:
</p>
<table>
<tr>
<td>
<img src="Gentium_o_fitted.png" alt="Gentium period"/>
</td>
</tr>
</table>
<p>
And here is how it looks at various resolutions from 30 ppem to
200 ppem. The pattern of pixels corresponds more closely to the
original outline as the resolution goes up:
</p>
<table>
<tr>
<td>
<img src="Gentium_o_cascade.png" alt="Gentium period"/>
</td>
</tr>
</table>
</div>
</body>
</html>
|
