Split C++ (godot-cpp) and GDExtension system info into separate categories, children of Scripting.

tutorials/scripting/cpp/about_godot_cpp.rst

@@ -0,0 +1,96 @@
+.. _doc_about_godot_cpp:
+
+About godot-cpp
+===============
+
+`godot-cpp <https://github.com/godotengine/godot-cpp>`__ are the official C++ GDExtension bindings, maintained
+as part of the Godot project.
+
+godot-cpp is built with the :ref:`GDExtension system <doc_gdextension>`, which allows access to Godot in almost the
+same way as :ref:`modules <doc_custom_modules_in_cpp>`: A lot of `engine code <https://github.com/godotengine/godot>`__
+can be used in your godot-cpp project almost exactly as it is.
+
+In particular, godot-cpp has access to all functions that :ref:`GDScript <doc_gdscript>` and :ref:`C# <doc_c_sharp>`
+have, and additional access to a few more for fast low-level access of data, or deeper integration with Godot.
+
+Differences between godot-cpp and C++ modules
+---------------------------------------------
+
+You can use both `godot-cpp <https://github.com/godotengine/godot-cpp>`__
+and :ref:`C++ modules <doc_custom_modules_in_cpp>` to run C or C++ code in a Godot project.
+
+They also both allow you to integrate third-party libraries into Godot. The one
+you should choose depends on your needs.
+
+.. warning::
+
+    godot-cpp is currently *experimental*, which means that we may
+    break compatibility in order to fix major bugs or include critical features.
+
+
+Advantages of godot-cpp
+~~~~~~~~~~~~~~~~~~~~~~~
+
+Unlike modules, godot-cpp (and GDExtensions, in general) don't require
+compiling the engine's source code, making it easier to distribute your work.
+It gives you access to most of the API available to GDScript and C#, allowing
+you to code game logic with full control regarding performance. It's ideal if
+you need high-performance code you'd like to distribute as an add-on in the
+:ref:`asset library <doc_what_is_assetlib>`.
+
+Also:
+
+- You can use the same compiled godot-cpp library in the editor and exported
+  project. With C++ modules, you have to recompile all the export templates you
+  plan to use if you require its functionality at runtime.
+- godot-cpp only requires you to compile your library, not the whole engine.
+  That's unlike C++ modules, which are statically compiled into the engine.
+  Every time you change a module, you need to recompile the engine. Even with
+  incremental builds, this process is slower than using godot-cpp.
+
+Advantages of C++ modules
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+We recommend :ref:`C++ modules <doc_custom_modules_in_cpp>` in cases where
+godot-cpp (or another GDExtension system) isn't enough:
+
+- C++ modules provide deeper integration into the engine. GDExtension's access
+  is not as deep as static modules.
+- You can use C++ modules to provide additional features in a project without
+  carrying native library files around. This extends to exported projects.
+
+.. note::
+
+    If you notice that specific systems are not accessible via godot-cpp
+    but are via custom modules, feel free to open an issue on the
+    `godot-cpp repository <https://github.com/godotengine/godot-cpp>`__
+    to discuss implementation options for exposing the missing functionality.
+
+.. _doc_what_is_gdextension_version_compatibility:
+
+Version compatibility
+---------------------
+
+Usually, GDExtensions targeting an earlier version of Godot will work in later
+minor versions, but not vice-versa. For example, a GDExtension targeting Godot 4.2
+should work just fine in Godot 4.3, but one targeting Godot 4.3 won't work in Godot 4.2.
+
+For this reason, when creating GDExtensions, you may want to target the lowest version of
+Godot that has the features you need, *not* the most recent version of Godot. This can
+save you from needing to create multiple builds for different versions of Godot.
+
+However, GDExtension is currently *experimental*, which means that we may
+break compatibility in order to fix major bugs or include critical features.
+For example, GDExtensions created for Godot 4.0 aren't compatible with Godot
+4.1 (see :ref:`updating_your_gdextension_for_godot_4_1`).
+
+GDExtensions are also only compatible with engine builds that use the same
+level of floating-point precision the extension was compiled for. This means
+that if you use an engine build with double-precision floats, the extension must
+also be compiled for double-precision floats and use an ``extension_api.json``
+file generated by your custom engine build. See :ref:`doc_large_world_coordinates`
+for details.
+
+Generally speaking, if you build a custom version of Godot, you should generate an
+``extension_api.json`` from it for your GDExtensions, because it may have some differences
+from official Godot builds.