document libraqm/fribidi linking, support fribidi-0.dll on Windows

docs/installation.rst

@@ -57,8 +57,9 @@ Windows Installation
 
 We provide Pillow binaries for Windows compiled for the matrix of
 supported Pythons in both 32 and 64-bit versions in the wheel format.
-These binaries have all of the optional libraries included except
+These binaries include support for all optional libraries except
-for raqm, libimagequant, and libxcb::
+libimagequant and libxcb. Raqm support requires
+fribidi to be installed separately::
 
     python3 -m pip install --upgrade pip
     python3 -m pip install --upgrade Pillow
@@ -71,8 +72,8 @@ macOS Installation
 
 We provide binaries for macOS for each of the supported Python
 versions in the wheel format. These include support for all optional
-libraries except libimagequant and libxcb. Raqm support requires
+libraries except libimagequant. Raqm support requires
-libraqm, fribidi, and harfbuzz to be installed separately::
+fribidi to be installed separately::
 
     python3 -m pip install --upgrade pip
     python3 -m pip install --upgrade Pillow
@@ -83,7 +84,7 @@ Linux Installation
 We provide binaries for Linux for each of the supported Python
 versions in the manylinux wheel format. These include support for all
 optional libraries except libimagequant. Raqm support requires
-libraqm, fribidi, and harfbuzz to be installed separately::
+fribidi to be installed separately::
 
     python3 -m pip install --upgrade pip
     python3 -m pip install --upgrade Pillow
@@ -191,11 +192,15 @@ Many of Pillow's features require external libraries:
   * libraqm depends on the following libraries: FreeType, HarfBuzz,
     FriBiDi, make sure that you install them before installing libraqm
     if not available as package in your system.
-  * setting text direction or font features is not supported without
+  * Setting text direction or font features is not supported without libraqm.
-    libraqm.
+  * Pillow wheels since version 8.2.0 include a modified version of libraqm that
-  * libraqm is dynamically loaded in Pillow 5.0.0 and above, so support
+    loads libfribidi at runtime if it is installed.
-    is available if all the libraries are installed.
+    On Windows this requires compiling FriBiDi and installing ``fribidi.dll``
-  * Windows support: Raqm is not included in prebuilt wheels
+    into a directory listed in the `Dynamic-Link Library Search Order (Microsoft Docs)
+    <https://docs.microsoft.com/en-us/windows/win32/dlls/dynamic-link-library-search-order#search-order-for-desktop-applications>`_
+    (``fribidi-0.dll`` or ``libfribidi-0.dll`` are also detected).
+    See `Build Options`_ to see how to build this version.
+  * Previous versions of Pillow (5.0.0 to 8.1.2) linked libraqm dynamically at runtime.
 
 * **libxcb** provides X11 screengrab support.
 
@@ -244,6 +249,12 @@ Build Options
   an exception if the libraries are not found. Webpmux (WebP metadata)
   relies on WebP support. Tcl and Tk also must be used together.
 
+* Build flags: ``--vendor-raqm --vendor-fribidi``
+  These flags are used to compile a modified version of libraqm and
+  a shim that dynamically loads libfribidi at runtime. These are
+  used to compile the standard Pillow wheels. Compiling libraqm requires
+  a C99-compliant compiler.
+
 * Build flag: ``--disable-platform-guessing``. Skips all of the
   platform dependent guessing of include and library directories for
   automated build systems that configure the proper paths in the

docs/releasenotes/8.2.0.rst

@@ -91,6 +91,24 @@ TODO
 Other Changes
 =============
 
+Libraqm and FriBiDi linking
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The way the libraqm dependency for complex text scripts is linked has been changed:
+
+Source builds will now link against the system version of libraqm at build time
+rather than at runtime by default.
+
+Binary wheels now include a statically linked modified version of libraqm that
+links against FriBiDi at runtime instead. This change is intended to address
+issues with the previous implementation on some platforms. These are created
+by building Pillow with the new build flags ``--vendor-raqm --vendor-fribidi``.
+
+Windows users will now need to install ``fribidi.dll`` (or ``fribidi-0.dll``) only,
+``libraqm.dll`` is no longer used.
+
+See :doc:`installation documentation<../installation>` for more information.
+
 PyQt6
 ^^^^^
 

src/thirdparty/fribidi-shim/fribidi.c

@@ -56,6 +56,9 @@ int load_fribidi(void) {
     error = error || (func == 0);
 
     p_fribidi = LoadLibrary("fribidi");
+    if (!p_fribidi) {
+        p_fribidi = LoadLibrary("fribidi-0");
+    }
     /* MSYS2 */
     if (!p_fribidi) {
         p_fribidi = LoadLibrary("libfribidi-0");

winbuild/build.rst

@@ -87,7 +87,7 @@ and install Pillow in develop mode (instead of ``python3 -m pip install --editab
 Testing Pillow
 --------------
 
-Some binary dependencies (e.g. ``libraqm.dll``) will be stored in the
+Some binary dependencies (e.g. ``fribidi.dll``) will be stored in the
 ``winbuild\build\bin`` directory; this directory should be added to ``PATH``
 before running tests.