Disable filib shared lib for windows

Author: zfergus

README.md

@@ -84,6 +84,19 @@ The following dependencies are optionally used based on CMake options:
 * [filib](https://github.com/zfergus/filib): interval arithmetic for nonlinear trajectories/CCD
     * Enable by using the CMake option `IPC_TOOLKIT_WITH_FILIB`
     * Enabled by default
+    * NOTE: filib is licensed under LGPL-2.1 and as such it is required to be dynamically linked. We enable this by default for Linux and MacOS. However, for Windows, we disable this by default because it requires copying the DLLs to the binary directory. To enable this, set the CMake option `FILIB_BUILD_SHARED_LIBS` to `ON` and add this CMake code to copy the DLLs to the binary directory:
+    ```cmake
+    if(WIN32)
+      # Copy DLLs to the output directory
+      add_custom_command(
+        TARGET ${MY_EXE_TARGET} POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different $<TARGET_RUNTIME_DLLS:${MY_EXE_TARGET}> $<TARGET_FILE_DIR:${MY_EXE_TARGET}>
+        COMMAND_EXPAND_LISTS
+      )
+    endif()
+    ```
+    * where `${MY_EXE_TARGET}` is the name of your executable target. If you know a better way to handle this, please [let us know](https://github.com/ipc-sim/ipc-toolkit/discussions)!
+    * If you would rather avoid LGPL code entirely, you can disable filib by setting `IPC_TOOLKIT_WITH_FILIB` to `OFF`. With this option disabled, CMake will not download or use any of filib's code.
 * [rational-cpp](https://github.io/zfergus/rational-cpp): rational arithmetic used for exact intersection checks
     * Enable by using the CMake option `IPC_TOOLKIT_WITH_RATIONAL_INTERSECTION`
     * Requires [GMP](https://gmplib.org/) to be installed at a system level

cmake/recipes/filib.cmake

@@ -6,8 +6,17 @@ endif()
 
 message(STATUS "Third-party: creating target 'filib::filib'")
 
-# This has to be set to ON to avoid licensing IPC Toolkit under LGPL
-set(FILIB_BUILD_SHARED_LIB ON CACHE BOOL "Build shared library" FORCE)
+# filib should be built as a shared library to avoid licensing IPC Toolkit under LGPL
+if(WIN32 AND NOT IPC_TOOLKIT_TOPLEVEL_PROJECT)
+  # Setting up proper linkage on Windows is a bit tricky, so we'll just use a
+  # static library by default and provide instructions on how to build as a
+  # shared library in the README.
+  option(FILIB_BUILD_SHARED_LIB "Build shared library" OFF)
+else()
+  # NOTE: Our Windows CMake is properly configured to build shared libraries for
+  #       OUR applications and python bindings.
+  option(FILIB_BUILD_SHARED_LIB "Build shared library" ON)
+endif()
 
 include(CPM)
 CPMAddPackage("gh:zfergus/filib#03e4eb0fc59399bd0003f8efd3179078195df49f")