POC code for working with libgodot

Author: touilleMan

src/_gdpy_libgodot.pyx

@@ -0,0 +1,128 @@
+from libc.stdlib cimport malloc, free
+from threading import Lock
+from contextlib import contextmanager
+
+from godot.hazmat.gdextension_interface cimport *
+from godot.classes cimport BaseGDObject
+
+
+# LibGodot API
+cdef extern from "*":
+    ctypedef struct LibGodotExtensionParameter:
+        const char* key
+        void* val
+
+    GDExtensionObjectPtr libgodot_create_godot_instance(int p_argc, char *p_argv[], GDExtensionInitializationFunction p_init_func, LibGodotExtensionParameter *p_params)
+    void libgodot_destroy_godot_instance(GDExtensionObjectPtr p_godot_instance)
+
+
+# Godot uses global variables, hence only a single instance can be created
+cdef object _libgodot_instance = None
+cdef object _libgodot_init_lock = Lock()
+
+
+@contextmanager
+def create_godot_instance(argv: list[str]):
+    global _libgodot_instance
+
+    _libgodot_init_lock.acquire()
+
+    if _libgodot_instance is not None:
+        raise RuntimeError(f"Only a single instance of Godot can exist at once ! ({_libgodot_instance!r} already exist)")
+
+    cdef GDExtensionObjectPtr gd_instance = _create_godot_instance(argv)
+    if gd_instance == NULL:
+        raise RuntimeError("Failed to create Godot instance")
+
+    try:
+        from godot.classes import GodotInstance
+        cdef BaseGDObject instance = GodotInstance.__new__(GodotInstance)
+        _libgodot_instance = instance
+
+        _libgodot_init_lock.release()
+
+        yield instance
+
+    finally:
+        with _libgodot_init_lock:
+            libgodot_destroy_godot_instance(instance._gd_instance)
+            _libgodot_instance = None
+
+
+cdef GDExtensionObjectPtr _create_godot_instance(argv: list[str]):
+    # Convert argv Python `list[str]` into C `char*[]`
+    pybytes_argv = [
+        a.encode("utf8") for a in argv
+    ]
+    cdef int length = len(argv)
+    cdef char **c_argv = <char **>malloc(length * sizeof(char*))
+    assert c_argv != NULL
+    try:
+        for i in range(length):
+            c_argv[i] = <const char*>pybytes_argv
+
+        # `c_argv` is ready, now we can initialize Godot instance !
+        return libgodot_create_godot_instance(
+            len(argv),
+            c_argv,
+            pythonscript_init,
+            NULL
+        )
+
+    finally:
+        free(c_argv)
+
+
+#
+# Callbacks used by Godot on instance creation
+#
+
+
+# Those symbols are defined in `pythonscript_gdextension_ptrs.c` which is
+# going to be compiled together with this file into a single shared library.
+cdef extern from "*":
+    const GDExtensionInterfaceGetProcAddress pythonscript_gdptr_get_proc_address
+    const GDExtensionClassLibraryPtr pythonscript_gdptr_library
+    void init_pythonscript_gdextension()
+
+
+cdef public GDExtensionBool pythonscript_init(
+    const GDExtensionInterfaceGetProcAddress p_get_proc_address,
+    const GDExtensionClassLibraryPtr p_library,
+    GDExtensionInitialization *r_initialization
+):
+    print('[libgodot] pythonscript_init()', flush=True)
+
+    # `pythonscript_gdptr_*` must be set as early as possible given it is never
+    # null-pointer checked, especially in the Cython modules.
+    # Note we start by setting only `get_proc_address`&`library` since it is the
+    # minimum we need to check Godot compatibility, and only after that we proceed
+    # with the rest of the pointers.
+    pythonscript_gdptr_get_proc_address = p_get_proc_address
+    pythonscript_gdptr_library = p_library
+
+    # Initialize the rest of the `pythonscript_gdptr_*` pointers
+    init_pythonscript_gdextension()
+
+    # Initialize as early as possible, this way we can have 3rd party plugins written
+    # in Python/Cython that can do things at this level
+    r_initialization.minimum_initialization_level  = GDEXTENSION_INITIALIZATION_CORE
+	r_initialization.userdata = NULL
+    r_initialization.initialize = _initialize
+    r_initialization.deinitialize = _deinitialize
+
+
+cdef void _initialize(void *userdata, GDExtensionInitializationLevel p_level):
+    print(f'[libgodot] _initialize({p_level})', flush=True)
+
+    import godot._lang
+    pythonscript_initialize = <void(*)(int)>godot._lang.pythonscript_initialize_function_ptr
+    pythonscript_initialize(p_level);
+
+
+cdef void _deinitialize(void *userdata, GDExtensionInitializationLevel p_level):
+    print(f'[libgodot] _deinitialize({p_level})', flush=True)
+
+    import godot._lang
+    pythonscript_deinitialize = <void(*)(int)>godot._lang.pythonscript_deinitialize_function_ptr
+    pythonscript_deinitialize(p_level);