Improve cross-compilation

Author: DataTriny

bindings/c/README.md

@@ -4,7 +4,7 @@ These are the bindings to use AccessKit from other languages through FFI such as
 
 ## How to use in a CMake project
 
-Decompress an accesskit_c release and place the resulting folder somewhere:
+Decompress an accesskit_c release and place the resulting folder somewhere either:
 
 - already known by CMake,
 - listed in your `CMAKE_PREFIX_PATH`,
@@ -46,3 +46,17 @@ Once inside the `bindings/c` directory, CMake can be used like this to build the
 cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
 cmake --build build
 ```
+
+### Notes on cross-compiling
+
+On Windows, you will need to pass the `-A` flag when configuring the project. For instance, to target ARM64:
+
+```
+cmake -S . -B build -A ARM64
+```
+
+On other platforms you will have to specify which Rust target to use, as well as tell CMake for which architecture to compile. Here is how you would cross-compile for Linux X86 from Linux AMD64:
+
+```
+cmake -S . -B build -DCMAKE_SYSTEM_NAME=Linux -DCMAKE_SYSTEM_PROCESSOR=x86 -DRust_CARGO_TARGET=i686-unknown-linux-gnu
+```

bindings/c/accesskit-config.cmake

@@ -12,7 +12,11 @@ elseif (WIN32)
     endif()
     if (CMAKE_VS_PLATFORM_NAME)
         string(TOLOWER "${CMAKE_VS_PLATFORM_NAME}" LOWER_VS_PLATFORM_NAME)
-        if ("${LOWER_VS_PLATFORM_NAME}" STREQUAL "arm64")
+        if ("${LOWER_VS_PLATFORM_NAME}" STREQUAL "win32")
+            set(_ACCESSKIT_ARCH x86)
+        elseif("${LOWER_VS_PLATFORM_NAME}" STREQUAL "x64")
+            set(_ACCESSKIT_ARCH x86_64)
+        elseif ("${LOWER_VS_PLATFORM_NAME}" STREQUAL "arm64")
             set(_ACCESSKIT_ARCH "arm64")
         endif()
     endif()
@@ -21,12 +25,12 @@ if (NOT _ACCESSKIT_TOOLCHAIN)
     set(_ACCESSKIT_TOOLCHAIN "")
 endif()
 if (NOT _ACCESSKIT_ARCH)
-    if (CMAKE_SYSTEM_PROCESSOR MATCHES "^(AMD64|amd64|x86_64)$")
-        set(_ACCESSKIT_ARCH "x86_64")
+   if (CMAKE_SYSTEM_PROCESSOR MATCHES "^(AMD64|amd64|x86_64)$")
+        set(_ACCESSKIT_ARCH x86_64)
     elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^(ARM64|arm64|aarch64)$")
-        set(_ACCESSKIT_ARCH "arm64")
+        set(_ACCESSKIT_ARCH arm64)
     elseif (CMAKE_SYSTEM_PROCESSOR MATCHES "^(X86|x86|i686)$")
-        set(_ACCESSKIT_ARCH "x86")
+        set(_ACCESSKIT_ARCH x86)
     endif()
 endif()
 set(ACCESSKIT_LIBRARIES_DIR "${CMAKE_CURRENT_LIST_DIR}/lib/${_ACCESSKIT_OS}/${_ACCESSKIT_ARCH}/${_ACCESSKIT_TOOLCHAIN}")