Paragraph Layout

This page is about the Paragraph Layout library that is available in ICU4C/C++.

For information about the deprecated Line Layout Engine, including its deprecation notice, see: Layout Engine.

About the Paragraph Layout library

  • The ICU Line LayoutEngine works on small chunks - unidirectional runs. It does not layout text at the paragraph level.
  • The ParagraphLayout object will analyze the text into runs of text in the same font, script and direction, and will create a LayoutEngine object for each run. The LayoutEngine will transform the characters into glyph codes in visual order. Clients can use this to break a paragraph into lines, and to display the glyphs in each line.
  • Also see the ParagraphLayout API Docs

Building the Paragraph Layout library with HarfBuzz

While the ICU LayoutEngine is deprecated as of ICU 54, the ICU *Paragraph *Layout library is not. The Paragraph Layout library must now be built using the HarfBuzz engine instead of the ICU LayoutEngine.

UNIX Makefile instructions / Cygwin / Msys / etc. (ICU 54+)

The following steps must be completed in order:

  1. Build and install a complete ICU with the --disable-layout --disable-layoutex switches passed to configure
  2. Build and install HarfBuzz - ‚Äč (HarfBuzz's use of ICU may be enabled or disabled at your choice)
  3. Build and install the icu-le-hb library.
  4. Now, rerun “configure” on the exact same ICU workspace used above:
    • with “icu-le-hb” AND the above-mentioned installed ICU available via pkg-config ( pkg-config --modversion icu-le-hb should return a version, such as “0.0.0” )
    • with the --disable-layout --enable-layoutex switches passed to configure
  5. next, run make install JUST in the source/layoutex directory, to install libiculx and icu-lx.pc

The above steps will produce a libiculx library that depends on HarfBuzz.

If pkg-config visible installation is not suitable for step 4, you may also manually set the following variables when building ICU in step 5:

  • set ICULEHB_CFLAGS to the appropriate include path for icu-le-hb ( such as -I/usr/local/include/icu-le-hb )
  • set ICULEHB_LIBS to link against icu-le-hb and dependents as needed (such as -L/usr/local/lib -licu-le-hb )