Document font backends for Cairo and/or HarfBuzz

* doc/lispref/frames.texi (Font and Color Parameters): Mention xfthb, ftcr,
and ftcrhb font backends.

diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index 9b3e02f4de03d4b21be4871fad05561f44efd4bc..c94b4e67aed18ea88a196790999c3081e0237b5e 100644 (file)
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -2279,12 +2279,17 @@ variable do not take effect immediately, only when you specify the
 @item font-backend
 A list of symbols, specifying the @dfn{font backends} to use for
 drawing fonts in the frame, in order of priority.  On X, there are
-currently two available font backends: @code{x} (the X core font
-driver) and @code{xft} (the Xft font driver).  On MS-Windows, there are
-currently two available font backends: @code{gdi} and
-@code{uniscribe} (@pxref{Windows Fonts,,, emacs, The GNU Emacs
-Manual}).  On other systems, there is only one available font backend,
-so it does not make sense to modify this frame parameter.
+currently three available font backends if Emacs was built without the
+Cairo drawing: @code{x} (the X core font driver), @code{xft} (the Xft
+font driver), and @code{xfthb} (the Xft font driver with HarfBuzz text
+shaping).  If built with the Cairo drawing, then there are two
+available font backends: @code{ftcr} (the FreeType font driver on
+Cairo) and @code{ftcrhb} (the FreeType font driver on Cairo with
+HarfBuzz text shaping).  On MS-Windows, there are currently two
+available font backends: @code{gdi} and @code{uniscribe}
+(@pxref{Windows Fonts,,, emacs, The GNU Emacs Manual}).  On other
+systems, there is only one available font backend, so it does not make
+sense to modify this frame parameter.
 
 @vindex background-mode@r{, a frame parameter}
 @item background-mode