|  |  |  |  | 
      The core of the HarfBuzz shaping API is the function
      hb_shape(). 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.
    
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.
      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 Default
      Ignorable codepoints, and to modify the cluster-merging
      behavior for the buffer. For shaped output buffers, the
      individual X and Y offsets and advances
      (the logical dimensions) of each glyph are 
      accessible. HarfBuzz also flags glyphs as
      UNSAFE_TO_BREAK if breaking the string at
      that glyph (e.g., in a line-breaking or hyphenation process)
      would require re-shaping the text.
    
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.
      Although the default hb_shape() 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. 
    
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.
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.