Use CPack for Windows packaging

src/CMakeLists.txt

@@ -102,9 +102,39 @@ add_executable(rgbgfx $<TARGET_OBJECTS:common>
     "verbosity.cpp"
 )
 
-install(TARGETS rgbasm rgblink rgbfix rgbgfx RUNTIME)
+install(TARGETS rgbasm rgblink rgbfix rgbgfx RUNTIME COMPONENT binaries)
 # Tests expect the binaries to end up in-source; this is more acceptable than the entire artifact dir.
 set_target_properties(rgbasm rgblink rgbfix rgbgfx PROPERTIES
 # The generator expression (even if a no-op) stops muti-config generators using a of "per-configuration subdirectory".
                       RUNTIME_OUTPUT_DIRECTORY $<1:${CMAKE_SOURCE_DIR}>)
 target_link_libraries(rgbgfx PRIVATE PNG::PNG)
+
+# On Windows, you don't link against DLLs directly, but against an import library for that DLL.
+# This leads to, sometimes, the DLL being stored in a directory far away from the import library itself!
+set(DLL_SEARCH_DIRS CACHE PATH "List of directories in which DLLs will be searched")
+cmake_path(CONVERT "${DLL_SEARCH_DIRS}" TO_CMAKE_PATH_LIST search_dirs NORMALIZE)
+# TODO: we've only tested this with MinGW, but it may not work with other uses of the variable.
+#       Anyone who knows how to handle this better, feel free to submit a patch!
+if(DEFINED CMAKE_FIND_ROOT_PATH)
+  list(APPEND search_dirs "${CMAKE_FIND_ROOT_PATH}/bin")
+endif()
+# Escape the search paths in a form that makes them suitable for splatting into the CMake install script.
+list(TRANSFORM search_dirs REPLACE "([\\$\"])" "\\\\1") # Neutralize escapes and variable refs...
+list(TRANSFORM search_dirs REPLACE "^(.+)\$" "\"\\1\"") # ...and quote each argument.
+list(JOIN search_dirs " " search_dirs_splat)
+# This is a modified version of the install code generated by
+# `install(TARGETS rgbgfx RUNTIME_DEPENDENCIES)`.
+# Unfortunately, that `install(TARGETS)` is outright not supported when cross-compiling,
+# and working around that has CMake fail to resolve the DLL locations with MinGW,
+# due to not specifying any `DIRECTORIES` and the system search path being ineffective.
+install(CODE "\
+file(GET_RUNTIME_DEPENDENCIES
+    RESOLVED_DEPENDENCIES_VAR rgbgfx_deps
+    EXECUTABLES \"$<TARGET_FILE:rgbgfx>\"
+    DIRECTORIES ${search_dirs_splat} \"$<TARGET_FILE_DIR:ZLIB::ZLIB>\" \"$<TARGET_FILE_DIR:PNG::PNG>\"
+    PRE_EXCLUDE_REGEXES \"^kernel32\\\\.dll$\" \"^msvcrt.?.?\\\\.dll\" \"^api-ms-win-.*\\\\.dll$\")
+  foreach(rgbgfx_dep IN LISTS rgbgfx_deps)
+    file(INSTALL DESTINATION \"$<INSTALL_PREFIX>/${CMAKE_INSTALL_BINDIR}\" TYPE SHARED_LIBRARY FILES \${rgbgfx_dep}
+      FOLLOW_SYMLINK_CHAIN)
+  endforeach()"
+        COMPONENT shared-libs EXCLUDE_FROM_ALL) # Most platforms install those separately.