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<div class="chapter">
<div class="titlepage"><div><div><h2 class="title">
<a name="hello-harfbuzz"></a>Hello, Harfbuzz</h2></div></div></div>
<div class="toc"><dl class="toc"><dt><span class="section"><a href="hello-harfbuzz.html#what-harfbuzz-doesnt-do">What Harfbuzz doesn't do</a></span></dt></dl></div>
<p>
Here's the simplest Harfbuzz that can possibly work. We will improve
it later.
</p>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Create a buffer and put your text in it.
</p></li></ol></div>
<pre class="programlisting">
#include <hb.h>
hb_buffer_t *buf;
buf = hb_buffer_create();
hb_buffer_add_utf8(buf, text, strlen(text), 0, strlen(text));
</pre>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem" value="2"><p>
Guess the script, language and direction of the buffer.
</p></li></ol></div>
<pre class="programlisting">
hb_buffer_guess_segment_properties(buf);
</pre>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem" value="3"><p>
Create a face and a font, using FreeType for now.
</p></li></ol></div>
<pre class="programlisting">
#include <hb-ft.h>
FT_New_Face(ft_library, font_path, index, &face)
hb_font_t *font = hb_ft_font_create(face);
</pre>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem" value="4"><p>
Shape!
</p></li></ol></div>
<pre class="programlisting">
hb_shape(font, buf, NULL, 0);
</pre>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem" value="5"><p>
Get the glyph and position information.
</p></li></ol></div>
<pre class="programlisting">
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);
</pre>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem" value="6"><p>
Iterate over each glyph.
</p></li></ol></div>
<pre class="programlisting">
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;
}
</pre>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem" value="7"><p>
Tidy up.
</p></li></ol></div>
<pre class="programlisting">
hb_buffer_destroy(buf);
hb_font_destroy(hb_ft_font);
</pre>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="what-harfbuzz-doesnt-do"></a>What Harfbuzz doesn't do</h2></div></div></div>
<p>
The code above will take a UTF8 string, shape it, and give you the
information required to lay it out correctly on a single
horizontal (or vertical) line using the font provided. That is the
extent of Harfbuzz's responsibility.
</p>
<p>
If you are implementing a text layout engine you may have other
responsibilities, that Harfbuzz will not help you with:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>
Harfbuzz won't help you with bidirectionality. If you want to
lay out text with mixed Hebrew and English, you will need to
ensure that the buffer provided to Harfbuzz has those
characters in the correct layout order. This will be different
from the logical order in which the Unicode text is stored. In
other words, the user will hit the keys in the following
sequence:
</p>
<pre class="programlisting">
A B C [space] ג ב א [space] D E F
</pre>
<p>
but will expect to see in the output:
</p>
<pre class="programlisting">
ABC אבג DEF
</pre>
<p>
This reordering is called <span class="emphasis"><em>bidi processing</em></span>
("bidi" is short for bidirectional), and there's an
algorithm as an annex to the Unicode Standard which tells you how
to reorder a string from logical order into presentation order.
Before sending your string to Harfbuzz, you may need to apply the
bidi algorithm to it. Libraries such as ICU and fribidi can do
this for you.
</p>
</li>
<li class="listitem"><p>
Harfbuzz won't help you with text that contains different font
properties. For instance, if you have the string "a
<span class="emphasis"><em>huge</em></span> breakfast", and you expect
"huge" to be italic, you will need to send three
strings to Harfbuzz: <code class="literal">a</code>, in your Roman font;
<code class="literal">huge</code> using your italic font; and
<code class="literal">breakfast</code> using your Roman font again.
Similarly if you change font, font size, script, language or
direction within your string, you will need to shape each run
independently and then output them independently. Harfbuzz
expects to shape a run of characters sharing the same
properties.
</p></li>
<li class="listitem">
<p>
Harfbuzz won't help you with line breaking, hyphenation or
justification. As mentioned above, it lays out the string
along a <span class="emphasis"><em>single line</em></span> of, notionally,
infinite length. If you want to find out where the potential
word, sentence and line break points are in your text, you
could use the ICU library's break iterator functions.
</p>
<p>
Harfbuzz can tell you how wide a shaped piece of text is, which is
useful input to a justification algorithm, but it knows nothing
about paragraphs, lines or line lengths. Nor will it adjust the
space between words to fit them proportionally into a line. If you
want to layout text in paragraphs, you will probably want to send
each word of your text to Harfbuzz to determine its shaped width
after glyph substitutions, then work out how many words will fit
on a line, and then finally output each word of the line separated
by a space of the correct size to fully justify the paragraph.
</p>
</li>
</ul></div>
<p>
As a layout engine implementor, Harfbuzz will help you with the
interface between your text and your font, and that's something
that you'll need - what you then do with the glyphs that your font
returns is up to you. The example we saw above enough to get us
started using Harfbuzz. Now we are going to use the remainder of
Harfbuzz's API to refine that example and improve our text shaping
capabilities.
</p>
</div>
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