You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
308 lines
11 KiB
308 lines
11 KiB
<?xml version="1.0"?>
|
|
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
|
|
<!ENTITY % local.common.attrib "xmlns:xi CDATA #FIXED 'http://www.w3.org/2003/XInclude'">
|
|
<!ENTITY version SYSTEM "version.xml">
|
|
]>
|
|
<chapter id="getting-started">
|
|
<title>Getting started with HarfBuzz</title>
|
|
<section>
|
|
<title>An overview of the HarfBuzz shaping API</title>
|
|
<para>
|
|
The core of the HarfBuzz shaping API is the function
|
|
<function>hb_shape()</function>. This function takes a font, a
|
|
buffer containing a string of Unicode codepoints and
|
|
(optionally) a list of font features as its input. It replaces
|
|
the codepoints in the buffer with the corresponding glyphs from
|
|
the font, correctly ordered and positioned, and with any of the
|
|
optional font features applied.
|
|
</para>
|
|
<para>
|
|
In addition to holding the pre-shaping input (the Unicode
|
|
codepoints that comprise the input string) and the post-shaping
|
|
output (the glyphs and positions), a HarfBuzz buffer has several
|
|
properties that affect shaping. The most important are the
|
|
text-flow direction (e.g., left-to-right, right-to-left,
|
|
top-to-bottom, or bottom-to-top), the script tag, and the
|
|
language tag.
|
|
</para>
|
|
|
|
<para>
|
|
For input string buffers, flags are available to denote when the
|
|
buffer represents the beginning or end of a paragraph, to
|
|
indicate whether or not to visibly render Unicode <literal>Default
|
|
Ignorable</literal> codepoints, and to modify the cluster-merging
|
|
behavior for the buffer. For shaped output buffers, the
|
|
individual X and Y offsets and <literal>advances</literal>
|
|
(the logical dimensions) of each glyph are
|
|
accessible. HarfBuzz also flags glyphs as
|
|
<literal>UNSAFE_TO_BREAK</literal> if breaking the string at
|
|
that glyph (e.g., in a line-breaking or hyphenation process)
|
|
would require re-shaping the text.
|
|
</para>
|
|
|
|
<para>
|
|
HarfBuzz also provides methods to compare the contents of
|
|
buffers, join buffers, normalize buffer contents, and handle
|
|
invalid codepoints, as well as to determine the state of a
|
|
buffer (e.g., input codepoints or output glyphs). Buffer
|
|
lifecycles are managed and all buffers are reference-counted.
|
|
</para>
|
|
|
|
<para>
|
|
Although the default <function>hb_shape()</function> function is
|
|
sufficient for most use cases, a variant is also provide that
|
|
lets you specify which of HarfBuzz's shapers to use on a buffer.
|
|
</para>
|
|
|
|
<para>
|
|
HarfBuzz can read TrueType fonts, TrueType collections, OpenType
|
|
fonts, and OpenType collections. Functions are provided to query
|
|
font objects about metrics, Unicode coverage, available tables and
|
|
features, and variation selectors. Individual glyphs can also be
|
|
queried for metrics, variations, and glyph names. OpenType
|
|
variable fonts are supported, and HarfBuzz allows you to set
|
|
variation-axis coordinates on font objects.
|
|
</para>
|
|
|
|
<para>
|
|
HarfBuzz provides glue code to integrate with various other
|
|
libraries, including FreeType, GObject, and CoreText. Support
|
|
for integrating with Uniscribe and DirectWrite is experimental
|
|
at present.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Terminology</title>
|
|
<para>
|
|
|
|
</para>
|
|
<variablelist>
|
|
<?dbfo list-presentation="blocks"?>
|
|
<varlistentry>
|
|
<term>script</term>
|
|
<listitem>
|
|
<para>
|
|
In text shaping, a <emphasis>script</emphasis> is a
|
|
writing system: a set of symbols, rules, and conventions
|
|
that is used to represent a language or multiple
|
|
languages.
|
|
</para>
|
|
<para>
|
|
In general computing lingo, the word "script" can also
|
|
be used to mean an executable program (usually one
|
|
written in a human-readable programming language). For
|
|
the sake of clarity, HarfBuzz documents will always use
|
|
more specific terminology when referring to this
|
|
meaning, such as "Python script" or "shell script." In
|
|
all other instances, "script" refers to a writing system.
|
|
</para>
|
|
<para>
|
|
For developers using HarfBuzz, it is important to note
|
|
the distinction between a script and a language. Most
|
|
scripts are used to write a variety of different
|
|
languages, and many languages may be written in more
|
|
than one script.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>shaper</term>
|
|
<listitem>
|
|
<para>
|
|
In HarfBuzz, a <emphasis>shaper</emphasis> is a
|
|
handler for a specific script-shaping model. HarfBuzz
|
|
implements separate shapers for Indic, Arabic, Thai and
|
|
Lao, Khmer, Myanmar, Tibetan, Hangul, Hebrew, the
|
|
Universal Shaping Engine (USE), and a default shaper for
|
|
non-complex scripts.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>cluster</term>
|
|
<listitem>
|
|
<para>
|
|
In text shaping, a <emphasis>cluster</emphasis> is a
|
|
sequence of codepoints that must be treated as an
|
|
indivisible unit. Clusters can include code-point
|
|
sequences that form a ligature or base-and-mark
|
|
sequences. Tracking and preserving clusters is important
|
|
when shaping operations might separate or reorder
|
|
code points.
|
|
</para>
|
|
<para>
|
|
HarfBuzz provides three cluster
|
|
<emphasis>levels</emphasis> that implement different
|
|
approaches to the problem of preserving clusters during
|
|
shaping operations.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>grapheme</term>
|
|
<listitem>
|
|
<para>
|
|
In linguistics, a <emphasis>grapheme</emphasis> is one
|
|
of the indivisible units that make up a writing system or
|
|
script. Often, graphemes are individual symbols (letters,
|
|
numbers, punctuation marks, logograms, etc.) but,
|
|
depending on the writing system, a particular grapheme
|
|
might correspond to a sequence of several Unicode code
|
|
points.
|
|
</para>
|
|
<para>
|
|
In practice, HarfBuzz and other text-shaping engines
|
|
are not generally concerned with graphemes. However, it
|
|
is important for developers using HarfBuzz to recognize
|
|
that there is a difference between graphemes and shaping
|
|
clusters (see above). The two concepts may overlap
|
|
frequently, but there is no guarantee that they will be
|
|
identical.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>syllable</term>
|
|
<listitem>
|
|
<para>
|
|
In linguistics, a <emphasis>syllable</emphasis> is an
|
|
a sequence of sounds that makes up a building block of a
|
|
particular language. Every language has its own set of
|
|
rules describing what constitutes a valid syllable.
|
|
</para>
|
|
<para>
|
|
For text-shaping purposes, the various definitions of
|
|
"syllable" are important because script-specific shaping
|
|
operations may be applied at the syllable level. For
|
|
example, a reordering rule might specify that a vowel
|
|
mark be reordered to the beginning of the syllable.
|
|
</para>
|
|
<para>
|
|
Syllables will consist of one or more Unicode code
|
|
points. The definition of a syllable for a particular
|
|
writing system might correspond to how HarfBuzz
|
|
identifies clusters (see above) for the same writing
|
|
system. However, it is important for developers using
|
|
HarfBuzz to recognize that there is a difference between
|
|
syllables and shaping clusters. The two concepts may
|
|
overlap frequently, but there is no guarantee that they
|
|
will be identical.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
</section>
|
|
|
|
|
|
<section>
|
|
<title>A simple shaping example</title>
|
|
|
|
<para>
|
|
Below is the simplest HarfBuzz shaping example possible.
|
|
</para>
|
|
<orderedlist numeration="arabic">
|
|
<listitem>
|
|
<para>
|
|
Create a buffer and put your text in it.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<programlisting language="C">
|
|
#include <hb.h>
|
|
hb_buffer_t *buf;
|
|
buf = hb_buffer_create();
|
|
hb_buffer_add_utf8(buf, text, -1, 0, -1);
|
|
</programlisting>
|
|
<orderedlist numeration="arabic">
|
|
<listitem override="2">
|
|
<para>
|
|
Set the script, language and direction of the buffer.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<programlisting language="C">
|
|
hb_buffer_set_direction(buf, HB_DIRECTION_LTR);
|
|
hb_buffer_set_script(buf, HB_SCRIPT_LATIN);
|
|
hb_buffer_set_language(buf, hb_language_from_string("en", -1));
|
|
</programlisting>
|
|
<orderedlist numeration="arabic">
|
|
<listitem override="3">
|
|
<para>
|
|
Create a face and a font, using FreeType for now.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<programlisting language="C">
|
|
#include <hb-ft.h>
|
|
FT_New_Face(ft_library, font_path, index, &face);
|
|
FT_Set_Char_Size(face, 0, 1000, 0, 0);
|
|
hb_font_t *font = hb_ft_font_create(face);
|
|
</programlisting>
|
|
<orderedlist numeration="arabic">
|
|
<listitem override="4">
|
|
<para>
|
|
Shape!
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<programlisting>
|
|
hb_shape(font, buf, NULL, 0);
|
|
</programlisting>
|
|
<orderedlist numeration="arabic">
|
|
<listitem override="5">
|
|
<para>
|
|
Get the glyph and position information.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<programlisting language="C">
|
|
hb_glyph_info_t *glyph_info = hb_buffer_get_glyph_infos(buf, &glyph_count);
|
|
hb_glyph_position_t *glyph_pos = hb_buffer_get_glyph_positions(buf, &glyph_count);
|
|
</programlisting>
|
|
<orderedlist numeration="arabic">
|
|
<listitem override="6">
|
|
<para>
|
|
Iterate over each glyph.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<programlisting language="C">
|
|
for (i = 0; i < glyph_count; ++i) {
|
|
glyphid = glyph_info[i].codepoint;
|
|
x_offset = glyph_pos[i].x_offset / 64.0;
|
|
y_offset = glyph_pos[i].y_offset / 64.0;
|
|
x_advance = glyph_pos[i].x_advance / 64.0;
|
|
y_advance = glyph_pos[i].y_advance / 64.0;
|
|
draw_glyph(glyphid, cursor_x + x_offset, cursor_y + y_offset);
|
|
cursor_x += x_advance;
|
|
cursor_y += y_advance;
|
|
}
|
|
</programlisting>
|
|
<orderedlist numeration="arabic">
|
|
<listitem override="7">
|
|
<para>
|
|
Tidy up.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
<programlisting language="C">
|
|
hb_buffer_destroy(buf);
|
|
hb_font_destroy(hb_ft_font);
|
|
</programlisting>
|
|
|
|
<para>
|
|
This example shows enough to get us started using HarfBuzz. In
|
|
the sections that follow, we will use the remainder of
|
|
HarfBuzz's API to refine and extend the example and improve its
|
|
text-shaping capabilities.
|
|
</para>
|
|
</section>
|
|
</chapter>
|