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Buffers containing input characters still need several properties set before HarfBuzz can shape their text correctly.
Initially, all buffers are set to the
HB_BUFFER_CONTENT_TYPE_INVALID content
type. After adding text, the buffer should be set to
HB_BUFFER_CONTENT_TYPE_UNICODE instead, which
indicates that it contains un-shaped input
characters. After shaping, the buffer will have the
HB_BUFFER_CONTENT_TYPE_GLYPHS content type.
hb_buffer_add_utf8() and the
other UTF functions set the content type of their buffer
automatically. But if you are reusing a buffer you may want to
check its state with
hb_buffer_get_content_type(buffer). If
necessary you can set the content type with
hb_buffer_set_content_type(buf, HB_BUFFER_CONTENT_TYPE_UNICODE);
to prepare for shaping.
Buffers also need to carry information about the script, language, and text direction of their contents. You can set these properties individually:
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));
However, since these properties are often repeated for
multiple text runs, you can also save them in a
hb_segment_properties_t for reuse:
hb_segment_properties_t *savedprops;
hb_buffer_get_segment_properties (buf, savedprops);
...
hb_buffer_set_segment_properties (buf2, savedprops);
HarfBuzz also provides getter functions to retrieve a buffer's direction, script, and language properties individually.
HarfBuzz recognizes four text directions in