Library support for emsdk (WebAssembly)

[coder137]

Was looking into creating GDExtension bindings with the Godot engine using this library

Reference (https://github.com/godotengine/godot-cpp)
Different platforms that should be supported (https://github.com/godotengine/godot-cpp/blob/master/test/project/example.gdextension)

When trying to compile with emsdk (https://emscripten.org/index.html) for a Web release I get compile errors.

By looking at the CMake scripts have removed the shared_library_* files from compilation as well as removed the SharedLibrary usage from the BehaviorTreeFactory::registerFromPlugin API.
According to me this was the only OS specific dependency of this project.

Questions

1. Are there any other change required to make WebAssembly builds compile?
2. Apart from Windows and Unix are other platforms supported? (Android, iOS, MacOS)

Additional Context

Current scons script

Import("env")

BEHAVIORTREE_FOLDER = "BehaviorTree.CPP"
env.Append(CPPPATH=[
    f"{BEHAVIORTREE_FOLDER}/include/",
    f"{BEHAVIORTREE_FOLDER}/3rdparty/",
    f"{BEHAVIORTREE_FOLDER}/3rdparty/lexy/include/"
])
localenv = env.Clone()

localenv.Append(CPPDEFINES=[
    "BTCPP_LIBRARY_VERSION=\\\"4.4.0\\\"",
    "LEXY_HAS_UNICODE_DATABASE=1"
])
# localenv.Append(CXXFLAGS=["-s ASYNCIFY"])
sources = [
    f"{BEHAVIORTREE_FOLDER}/src/action_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/basic_types.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/behavior_tree.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/blackboard.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/bt_factory.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/decorator_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/condition_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/control_node.cpp",
    # f"{BEHAVIORTREE_FOLDER}/src/shared_library.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/tree_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/script_parser.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/json_export.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/xml_parsing.cpp",

    f"{BEHAVIORTREE_FOLDER}/src/actions/test_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/actions/sleep_node.cpp",

    f"{BEHAVIORTREE_FOLDER}/src/decorators/delay_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/decorators/inverter_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/decorators/repeat_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/decorators/retry_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/decorators/timeout_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/decorators/subtree_node.cpp",

    f"{BEHAVIORTREE_FOLDER}/src/controls/if_then_else_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/fallback_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/parallel_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/parallel_all_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/reactive_sequence.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/reactive_fallback.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/sequence_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/sequence_star_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/switch_node.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/controls/while_do_else_node.cpp",

    f"{BEHAVIORTREE_FOLDER}/src/loggers/bt_cout_logger.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/loggers/bt_file_logger_v2.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/loggers/bt_minitrace_logger.cpp",
    f"{BEHAVIORTREE_FOLDER}/src/loggers/bt_observer.cpp",

    f"{BEHAVIORTREE_FOLDER}/3rdparty/tinyxml2/tinyxml2.cpp",
    f"{BEHAVIORTREE_FOLDER}/3rdparty/minitrace/minitrace.cpp",
]

# # TODO, Might need to check for WASM applications
# if env['PLATFORM'] == 'windows':
#     sources.append(f"{BEHAVIORTREE_FOLDER}/src/shared_library_WIN.cpp")
# else:
#     sources.append(f"{BEHAVIORTREE_FOLDER}/src/shared_library_UNIX.cpp")

libpath = localenv.File(
    f"bin/{localenv['platform']}/libbehaviortree_cpp{localenv['suffix']}{localenv['LIBSUFFIX']}")
library = localenv.StaticLibrary(
    target=libpath, source=sources)
print(library)

localenv.Default(library)
env.AppendUnique(LIBS=[libpath])

[coder137]

To get the library to compile with emscripten (https://emscripten.org/index.html), Made the following changes

Removed BT::SharedLibrary from registerFromPlugin

• This is an OS-specific feature that can be used only for WIN and UNIX systems

Removed minicoro.h usage

• Was giving error templates must have C++ linkage. The minicoro.h library uses extern "C", should use extern "C++" instead.
• This resulted in removing the entire CoroActionNode from the library

Deleted std::from_chars API when using emscripten

• In API Any::stringToNumber in safe_any.hpp,
  changed
  #if __has_include(<GL/gl.h>) to
  #if __has_include(<GL/gl.h>) && !defined(__EMSCRIPTEN__)

This library now compiles with the emscripten (em++) compiler.

According to me, For

• 1st change can be
  • Compiled out during the build system stage (files are not compiled and linked)
  • Under a compile flag like if defined(__EMSCRIPTEN__) to conditionally remove these features.
• 2nd change we could
  • conditionally remove this feature as well using if defined(__EMSCRIPTEN__)
  • add a fix using extern "C++" instead of extern "C" to remove compile errors
• Unsure about the impact of the 3rd change. Maybe there is a cleaner way to handle this conversion

@facontidavide Please let me know what you think.
I can make these changes for Webassembly compilation via a PR.

[facontidavide]

I am happy to accept a PR as long as all the changes are wrapped into an if defined(__EMSCRIPTEN__) section and nothing changes when compiling with a regular compiler

[facontidavide]

Any update on this?

[coder137]

Any update on this?

Had forgotten about this. Thanks for pinging.
Have made a PR where emsdk 3.1.47 can compile BehaviorTree.CPP as a static lib.