M0' scaffold: Godot 4.7 + GDExtension + libgr2 wired up (macOS)

- extension/: godot-cpp submodule (master, API 4.7), Metin2Model node
  registered, links xrender-poc/libgr2 via sibling-dir reference.
- project/: Godot 4.7 project — orbit camera + DirectionalLight3D (shadows)
  + WorldEnvironment/procedural sky + placeholder cube; main.gd probes the
  extension and can run libgr2 on a real .gr2 (MTGODOT_PROBE_GR2).
- build.sh one-shot build into project/bin/.
- docs/GODOT-POC-PLAN.md (phased: Phase 1 macOS -> M0'/M1/M2/M2.5).

Verified on this machine:
  [mtgodot] Metin2Model registered OK — libgr2 linked
  probe_gr2(warrior_cheongrin.gr2) -> gr2 OK: format_version=6 sections=8
  Metal Forward+ renders the scene (test/golden/m0-scaffold.png).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaHYEY9rwLWt21PULiYjeJ

extension/CMakeLists.txt

@@ -0,0 +1,37 @@
+# mtgodot GDExtension — M0' skeleton (registers Metin2Model, links libgr2).
+
+# --- godot-cpp (submodule @ master) ---
+# master has no per-minor branch; it ships bundled extension_api-4-*.json.
+# Pin to 4.7 to match the installed editor (4.7.1; patch-level ABI is compatible).
+set(GODOTCPP_API_VERSION "4.7" CACHE STRING "Target Godot API version" FORCE)
+add_subdirectory(godot-cpp)
+
+# --- libgr2 from the sibling xrender-poc repo ---
+# M0': plain sibling-directory reference (both repos live under .../mt/).
+# For a portable checkout, either git-submodule xrender-poc or vendor libgr2,
+# then pass -DXRENDER_POC_DIR=/path/to/xrender-poc.
+set(XRENDER_POC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../../xrender-poc"
+    CACHE PATH "Path to the xrender-poc repo (provides libgr2)")
+if(NOT EXISTS "${XRENDER_POC_DIR}/libgr2/CMakeLists.txt")
+    message(FATAL_ERROR
+        "libgr2 not found at '${XRENDER_POC_DIR}/libgr2'. "
+        "Pass -DXRENDER_POC_DIR=/path/to/xrender-poc")
+endif()
+add_subdirectory("${XRENDER_POC_DIR}/libgr2" "${CMAKE_CURRENT_BINARY_DIR}/libgr2")
+
+# --- the extension shared library ---
+add_library(mtgodot SHARED
+    src/register_types.cpp
+    src/metin2_model.cpp
+)
+target_compile_features(mtgodot PRIVATE cxx_std_20)
+target_link_libraries(mtgodot PRIVATE godot::cpp xrender::libgr2)
+
+# Drop the dylib straight into the Godot project where the .gdextension expects it:
+#   project/bin/libmtgodot.macos.template_debug.dylib   (Debug)
+#   project/bin/libmtgodot.macos.template_release.dylib (Release)
+set_target_properties(mtgodot PROPERTIES
+    PREFIX "lib"
+    OUTPUT_NAME "mtgodot.macos.$<IF:$<CONFIG:Release>,template_release,template_debug>"
+    LIBRARY_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/project/bin"
+)

extension/src/metin2_model.cpp

@@ -0,0 +1,39 @@
+#include "metin2_model.h"
+
+#include <godot_cpp/core/class_db.hpp>
+#include <godot_cpp/variant/utility_functions.hpp>
+
+#include <string>
+
+#include <gr2/gr2.h> // libgr2 (xrender-poc)
+
+using namespace godot;
+
+namespace mtgodot {
+
+Metin2Model::Metin2Model() = default;
+Metin2Model::~Metin2Model() = default;
+
+void Metin2Model::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("libgr2_info"), &Metin2Model::libgr2_info);
+	ClassDB::bind_method(D_METHOD("probe_gr2", "path"), &Metin2Model::probe_gr2);
+}
+
+String Metin2Model::libgr2_info() const {
+	// Forces a reference to a libgr2 symbol so the link is real, not dead-stripped.
+	return String("libgr2 linked; gr2::Magic enum size=") + itos((int)sizeof(gr2::Magic));
+}
+
+String Metin2Model::probe_gr2(const String &path) const {
+	gr2::LoadError err;
+	const std::string p(path.utf8().get_data());
+	auto file = gr2::File::load_path(p, &err);
+	if (!file) {
+		return vformat("gr2 load FAILED [%s]: %s",
+				String(err.stage.c_str()), String(err.message.c_str()));
+	}
+	return vformat("gr2 OK: format_version=%d sections=%d",
+			(int)file->format_version(), (int)file->sections().size());
+}
+
+} // namespace mtgodot

extension/src/metin2_model.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <godot_cpp/classes/node3d.hpp>
+#include <godot_cpp/variant/string.hpp>
+
+namespace mtgodot {
+
+// M0' placeholder node.
+//
+// Purpose at this milestone: prove the GDExtension registers a class the Godot
+// editor can instantiate, and that libgr2 is linked in and callable from here.
+// M1 replaces the body with real Skeleton3D / ArrayMesh construction
+// (see docs/GODOT-POC-PLAN.md §M1).
+class Metin2Model : public godot::Node3D {
+	GDCLASS(Metin2Model, godot::Node3D)
+
+public:
+	Metin2Model();
+	~Metin2Model() override;
+
+	// One-line tag proving libgr2 symbols resolved at link time.
+	godot::String libgr2_info() const;
+
+	// Parse a .gr2 with libgr2 and report a couple of counts (no scene build yet).
+	godot::String probe_gr2(const godot::String &path) const;
+
+protected:
+	static void _bind_methods();
+};
+
+} // namespace mtgodot

extension/src/register_types.cpp

@@ -0,0 +1,33 @@
+#include "register_types.h"
+
+#include <gdextension_interface.h>
+#include <godot_cpp/core/defs.hpp>
+#include <godot_cpp/godot.hpp>
+
+#include "metin2_model.h"
+
+using namespace godot;
+
+void initialize_mtgodot_module(ModuleInitializationLevel p_level) {
+	if (p_level != MODULE_INITIALIZATION_LEVEL_SCENE) {
+		return;
+	}
+	GDREGISTER_CLASS(mtgodot::Metin2Model);
+}
+
+void uninitialize_mtgodot_module(ModuleInitializationLevel p_level) {
+	(void)p_level;
+}
+
+extern "C" {
+GDExtensionBool GDE_EXPORT mtgodot_library_init(
+		GDExtensionInterfaceGetProcAddress p_get_proc_address,
+		const GDExtensionClassLibraryPtr p_library,
+		GDExtensionInitialization *r_initialization) {
+	godot::GDExtensionBinding::InitObject init_obj(p_get_proc_address, p_library, r_initialization);
+	init_obj.register_initializer(initialize_mtgodot_module);
+	init_obj.register_terminator(uninitialize_mtgodot_module);
+	init_obj.set_minimum_library_initialization_level(MODULE_INITIALIZATION_LEVEL_SCENE);
+	return init_obj.init();
+}
+}

extension/src/register_types.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include <godot_cpp/core/class_db.hpp>
+
+void initialize_mtgodot_module(godot::ModuleInitializationLevel p_level);
+void uninitialize_mtgodot_module(godot::ModuleInitializationLevel p_level);