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Improve writing style in "GDNative C++ example"

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Hugo Locurcio
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tutorials/plugins/gdnative/gdnative-cpp-example.rst
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@@ -5,27 +5,41 @@ GDNative C++ example
Introduction
------------
This tutorial builds on top of the information given in the :ref:`GDNative C example <doc_gdnative_c_example>` so we highly recommend you read that first.
The C++ bindings for GDNative are build on top of the nativescript GDNative API and provide a nicer way to "extend" nodes in Godot using C++. Basically this is the equivalent to writing GDScript scripts but in C++.
This tutorial builds on top of the information given in the
:ref:`GDNative C example <doc_gdnative_c_example>`, so we highly
recommend you read that first.
We'll be looking at nativescript 1.0 which is available in Godot 3.0. Godot 3.1 will see the introduction of nativescript 1.1 which has a number of improvements. We'll update this tutorial once that is officially released but the overal structure is much the same.
The C++ bindings for GDNative are built on top of the
NativeScript GDNative API and provide a nicer way to "extend" nodes
in Godot using C++. This is equivalent to writing scripts in GDScript,
but in C++ instead.
You can download the full example we'll be creating in this tutorial here: https://github.com/BastiaanOlij/gdnative_cpp_example
We'll be looking at NativeScript 1.0 which is available in Godot 3.0.
Godot 3.1 will see the introduction of NativeScript 1.1, which comes with a
number of improvements. We'll update this tutorial once it is
officially released, but the overall structure remains similar.
You can download the full example we'll be creating in this tutorial
`on GitHub <https://github.com/BastiaanOlij/gdnative_cpp_example>`_.
Setting up the project
----------------------
Setting up your project
-----------------------
There are a few prerequisites you'll need:
1) A Godot 3.x executable
2) a C++ compiler
3) scons as a build tool
4) a copy of the godot_headers repository you can find here: https://github.com/GodotNativeTools/godot_headers
5) a copy of the godot_cpp repository you can find here: https://github.com/GodotNativeTools/godot-cpp
- a Godot 3.x executable,
- a C++ compiler,
- SCons as a build tool,
- a copy of the `godot_headers repository <https://github.com/GodotNativeTools/godot_headers>`_,
- a copy of the `godot-cpp repository <https://github.com/GodotNativeTools/godot-cpp>`_.
See also http://docs.godotengine.org/en/latest/development/compiling/index.html as the build tools are identical to those you need to compile Godot from source.
See also :ref:`Compiling <toc-devel-compiling>` as the build tools are identical
to the ones you need to compile Godot from source.
You can just download these repositories from GitHub or let git do all the work for you. I've started to submodule them into my project folder. This is how I usually start my projects:
You can download these repositories from GitHub or let Git
do the work for you. If you are versioning your project using Git,
it is a good idea to add them as Git submodules:
.. code-block:: none
@@ -35,246 +49,331 @@ You can just download these repositories from GitHub or let git do all the work
git submodule add https://github.com/GodotNativeTools/godot_headers
git submodule add https://github.com/GodotNativeTools/godot-cpp
You don't have to do it this way but I've found it easiest to manage. If you decide to just download the repositories or just clone them into your folder, makes sure to keep the folder layout the same as I've setup here as much of the code we'll be showcasing here assumes the project has this layout.
If you decide to just download the repositories or clone them
into your project folder, make sure to keep the folder layout identical
to the one described here, as much of the code we'll be showcasing here
assumes the project follows this layout.
If you downloaded or cloned my example from the link specified in the introduction the submodules aren't automatically included. You will need to execute the following:
If you cloned the example from the link specified in
the introduction, the submodules are not automatically initialized.
You will need to execute the following commands:
.. code-block:: none
cd gdnative_cpp_example
git submodule init
git submodule update
git submodule --init update
This will trigger downloading these two repositories into your project folder.
This will clone these two repositories into your project folder.
Building the C++ bindings
-------------------------
Now that we've downloaded our prerequisites it is time to build our C++ bindings.
Now the repository contains a copy of the meta data for the current Godot release but if you need to build these bindings for a newer version of Godot you simply call the godot executable:
Now that we've downloaded our prerequisites, it is time to build
the C++ bindings.
The repository contains a copy of the metadata for the current Godot release,
but if you need to build these bindings for a newer version of Godot,
simply call the Godot executable:
.. code-block:: none
godot --gdnative-generate-json-api godot_api.json
And place the resulting godot_api.json file in our godot-cpp folder.
Place the resulting ``godot_api.json`` file in the ``godot-cpp/`` folder.
Now to generate and compile our bindings we do (do chose either Windows, Linux or OSX):
To generate and compile the bindings, use this command (replacing
``<platform>`` with ``windows``, ``x11`` or ``osx`` depending on your OS):
.. code-block:: none
cd godot-cpp
scons platform=windows/linux/osx headers=../godot_headers generate_bindings=yes
scons platform=<platform> headers=../godot_headers generate_bindings=yes
cd ..
This step will take a while but at the end of it, you should have static libraries you can compile into your project stored in godot-cpp/bin.
This step will take a while. When it is completed, you should have static
libraries that can be compiled into your project stored in ``godot-cpp/bin/``.
At some point we'll probably start making compiled binaries available for download so you can skip this whole section.
At some point in the future, compiled binaries will be available,
making this step optional.
Creating a simple plugin
------------------------
Now it's time to build an actual plugin.
To start we want to create an empty Godot project in which we'll be able to place a few files so open up Godot and create a new project. I like to place an demo project in my repository that shows how my GDNative module works so for our example we'll create a project in a folder called "demo" inside of our GDNative modules folder structure.
Now it's time to build an actual plugin. We'll start by creating an
empty Godot project in which we'll place a few files.
Inside our demo we'll create a scene with a single Node of type Node called "Main" and we'll save this as main.tscn. We'll come back to that later.
Open Godot and create a new project. For this example, we will place it
in a folder called ``demo`` inside our GDNative module's folder structure.
Back in the top-level gdnative module folder, we're also going to create a subfolder called ``src`` into which we'll place our source files.
In our demo project, we'll create a scene containing a Node called "Main"
and we'll save it as ``main.tscn``. We'll come back to that later.
You should now have ``demo``, ``godot-cpp``, ``godot_headers``, and ``src`` directories in your gdnative module.
Back in the top-level GDNative module folder, we're also going to create
a subfolder called ``src`` in which we'll place our source files.
In the ``src`` folder, we'll start with creating our header file for the GDNative node we'll be creating. This we'll call ``gdexample.h``:
You should now have ``demo``, ``godot-cpp``, ``godot_headers``,
and ``src`` directories in your GDNative module.
In the ``src`` folder, we'll start with creating our header file
for the GDNative node we'll be creating. We will name it ``gdexample.h``:
.. code:: C++
#ifndef GDEXAMPLE_H
#define GDEXAMPLE_H
#include <Godot.hpp>
#include <Sprite.hpp>
namespace godot {
class gdexample : public godot::GodotScript<Sprite> {
GODOT_CLASS(gdexample)
private:
float time_passed;
public:
static void _register_methods();
gdexample();
~gdexample();
void _process(float delta);
};
}
#endif
There are a few things of note to the above.
We're including ``Godot.hpp`` which contains all our basic definitions. After that we include ``Sprite.hpp`` which includes the bindings to our sprite class. This class we'll be extending in our module.
We're including ``Godot.hpp`` which contains all our basic definitions.
After that, we include ``Sprite.hpp`` which contains bindings
to the Sprite class. We'll be extending this class in our module.
We're using the namespace ``godot``, everything in GDNative is defined within this namespace.
We're using the namespace ``godot``, since everything in GDNative
is defined within this namespace.
Then we have our class definition and we see that we're inheriting from our Sprite but through a container class. We'll see a few side effects from this later on. This is also the main bit that is going to improve in nativescript 1.1.
The GODOT_CLASS macro sets up a few internal things for us.
Then we have our class definition, which inherits from our Sprite
through a container class. We'll see a few side effects of this later on.
This is also the main bit that is going to improve in NativeScript 1.1.
The ``GODOT_CLASS`` macro sets up a few internal things for us.
After that we declare a single member variables called ``time_passed``.
After that, we declare a single member variable called ``time_passed``.
In the next block we're defining our methods, we obviously have our constructor and destructor defined but there are two other functions that will likely look familiar to some.
In the next block we're defining our methods, we obviously have
our constructor and destructor defined, but there are two other
functions that will likely look familiar to some.
The first is ``_register_methods`` which is a static function that Godot will call to find out what our methods can be called on our native_script and what properties it has.
The second is our ``_process`` function which will work exactly the same as the ``_process`` function you're used to using in GDScript.
The first is ``_register_methods``, which is a static function that Godot
will call to find out which methods can be called on our NativeScript
and which properties it exposes. The second is our ``_process`` function,
which will work exactly the same as the ``_process`` function
you're used to in GDScript.
So, let's implement our functions by creating our ``gdexample.cpp`` file:
.. code:: C++
#include "gdexample.h"
using namespace godot;
void gdexample::_register_methods() {
register_method((char *)"_process", &gdexample::_process);
register_method((char *)"_process", &gdexample::_process);
}
gdexample::gdexample() {
// initialize any variables here
// Initialize any variables here
time_passed = 0.0;
}
gdexample::~gdexample() {
// add your cleanup here
// Add your cleanup procedure here
}
void gdexample::_process(float delta) {
time_passed += delta;
Vector2 new_position = Vector2(10.0 + (10.0 * sin(time_passed * 2.0)), 10.0 + (10.0 * cos(time_passed * 1.5)));
owner->set_position(new_position);
}
This one should be straight forward. We're implementing each method of our class that we defined in our header file. Of note is the ``register_method`` call that informs Godot that we have a ``_process`` method. We do not have to tell Godot about our constructor nor destructor.
This one should be straightforward. We're implementing each method of
our class that we defined in our header file.
Note that the ``register_method`` call **must** expose the ``_process`` method,
otherwise Godot will not be able to use it. However, we do not have to tell Godot
about our constructor and destructor.
The other method of note is our ``_process`` function where I'm simply keeping track of how much time has passed and calculating a new position for our sprite using a simple sine and cosine function.
What does stand out is calling ``owner->set_position`` to call one of the build in methods of our Sprite. This is because our class is a container class and owner points to the actual sprite node our script relates to.
Once we can use nativescript 1.1 we'll be able to call ``set_position`` directly on our class.
The other method of note is our ``_process`` function, which simply keeps track
of how much time has passed and calculates a new position for our sprite
using a simple sine and cosine function.
What stands out is calling ``owner->set_position`` to call one of the build
in methods of our Sprite. This is because our class is a container class;
``owner`` points to the actual Sprite node our script relates to.
In the upcoming NativeScript 1.1, ``set_position`` can be called
directly on our class.
Now there is one more C++ file we need that we call ``gdlibrary.cpp``. Our GDNative plugin can contain multiple native_scripts each one with their own header and source file like we've implemented ``gdexample`` up above. What we now need is a small bit of code that tells Godot about all the native_scripts in our GDNative plugin.
There is one more C++ file we need; we'll name it ``gdlibrary.cpp``.
Our GDNative plugin can contain multiple NativeScripts, each with their
own header and source file like we've implemented ``gdexample`` up above.
What we need now is a small bit of code that tells Godot about all the
NativeScripts in our GDNative plugin.
.. code:: C++
#include "gdexample.h"
extern "C" void GDN_EXPORT godot_gdnative_init(godot_gdnative_init_options *o) {
godot::Godot::gdnative_init(o);
}
extern "C" void GDN_EXPORT godot_gdnative_terminate(godot_gdnative_terminate_options *o) {
godot::Godot::gdnative_terminate(o);
}
extern "C" void GDN_EXPORT godot_nativescript_init(void *handle) {
godot::Godot::nativescript_init(handle);
godot::register_class<godot::gdexample>();
}
Note that we are not using our namespace here because the three functions implemented here need to be defined without a namespace.
Note that we are not using the ``godot`` namespace here, since the
three functions implemented here need to be defined without a namespace.
The ``godot_gdnative_init`` and ``godot_gdnative_terminate`` functions get called respectively when Godot loads our plugin and when it unloads it. All we're doing here is parse through to the functions in our bindings module that does some initialisation for us but you might have a need to setup more things.
The ``godot_gdnative_init`` and ``godot_gdnative_terminate`` functions
get called respectively when Godot loads our plugin and when it unloads it.
All we're doing here is parse through the functions in our bindings module
to initialize them, but you might have to set up more things depending
on your needs.
The important function is the third function called ``godot_nativescript_init``. Again we first call a function in our bindings library that does its usual stuff.
After that we call the function ``register_class`` for each of our classes in our library.
The important function is the third function called
``godot_nativescript_init``. We first call a function in our bindings
library that does its usual stuff. After that, we call the function
``register_class`` for each of our classes in our library.
Compiling our plugin
Compiling the plugin
--------------------
We can't really make pretty the ``SConstruct`` files used for building in scons. For the purpose of this example, just use this hardcoded build file we've prepared. We'll cover a more customizable, detailed example on how to use these build files in a subsequent tutorial: :download:`SConstruct <files/cpp_example/SConstruct>`
We cannot easily write by hand a ``SConstruct`` file that SCons would
use for building. For the purpose of this example, just use
:download:`this hardcoded SConstruct file <files/cpp_example/SConstruct>`
we've prepared. We'll cover a more customizable, detailed example on
how to use these build files in a subsequent tutorial.
Once you've downloaded the ``SConstruct`` file, place it in your gdnative module folder, beside ``godot-cpp``, ``godot_headers``, and ``demo``. Next just run:
Once you've downloaded the ``SConstruct`` file, place it in your
GDNative module folder besides ``godot-cpp``, ``godot_headers``
and ``demo``, then run:
.. code-block:: none
scons platform=windows/linux/osx
scons platform=<platform>
And our module should compile. You should now be able to find your module in ``demo/bin/<platform>``
You should now be able to find the module in ``demo/bin/<platform>``.
**Note**, we've compiled both godot-cpp and our gdexample library as debug builds. For release you should recompile them using the ``target=release`` switch.
**Note:** Here, we've compiled both godot-cpp and our gdexample library
as debug builds. For optimized builds, you should compile them using
the ``target=release`` switch.
Using your GDNative module
--------------------------
Using the GDNative module
-------------------------
Before we jump back into Godot we need to create two more files in ``demo/bin/`` . Both can now be created through the interface in Godot but I find it easier to just create them directly.
Before we jump back into Godot, we need to create two more files
in ``demo/bin/``. Both can be created using the Godot editor,
but it may be faster to create them directly.
The first is a file that lets Godot know what dynamic libraries should be loaded for each platform and is called ``gdexample.gdnlib``.
The first one is a file that lets Godot know what dynamic libraries
should be loaded for each platform and is called ``gdexample.gdnlib``.
.. code-block:: none
[general]
singleton=false
load_once=true
symbol_prefix="godot_"
[entry]
X11.64="res://bin/x11/libgdexample.so"
Windows.64="res://bin/win64/libgdexample.dll"
OSX.64="res://bin/osx/libgdexample.dylib"
[dependencies]
X11.64=[]
Windows.64=[]
OSX.64=[]
So what's in this file? Well there is a ``general`` section that controls how our module is loaded. It also contains a prefix section which we should leave on ``godot_`` for now. If you change this you'll need to rename various functions that are used as entry points. This was added for the iPhone platform because it doesn't allow dynamic libraries to be deployed and GDNative modules are statically linked.
This file contains a ``general`` section that controls how the module is loaded.
It also contains a prefix section which should be left on ``godot_`` for now.
If you change this, you'll need to rename various functions that are
used as entry points. This was added for the iPhone platform because it doesn't
allow dynamic libraries to be deployed, yet GDNative modules
are linked statically.
The ``entry`` section is the important bit, it tells Godot for each platform we support where our dynamic library is on disk. It will also result in just that file being exported when you export your game.
The ``entry`` section is the important bit: it tells Godot the location of
the dynamic library in the project's filesystem for each supported platform.
It will also result in *just* that file being exported when you export the
project, which means the data pack won't contain libraries that are
incompatible with the target platform.
Finally the ``dependencies`` section allows you to name additional dynamic libraries that should be included as well. This is important when your GDNative plugin implements someone elses library and requires you to supply a 3rd party dynamic library with your game.
Finally, the ``dependencies`` section allows you to name additional
dynamic libraries that should be included as well. This is important when
your GDNative plugin implements someone else's library and requires you
to supply a third-party dynamic library with your project.
If you double click on the ``gdexample.gdnlib`` file within Godot you'll see there are far more options to set:
If you double click on the ``gdexample.gdnlib`` file within Godot,
you'll see there are far more options to set:
.. image:: img/gdnative_library.png
The second file we need to create is a file we need to create for each native_script we've added to our plugin. We name it ``gdexample.gdns`` for our gdexample native_script.
The second file we need to create is a file used by each NativeScript
we've added to our plugin. We'll name it ``gdexample.gdns`` for our
gdexample NativeScript.
.. code-block:: none
[gd_resource type="NativeScript" load_steps=2 format=2]
[ext_resource path="res://bin/gdexample.gdnlib" type="GDNativeLibrary" id=1]
[resource]
resource_name = "gdexample"
class_name = "gdexample"
library = ExtResource( 1 )
_sections_unfolded = [ "Resource" ]
This is a standard Godot resource and you could just create that directly inside of your scene but having this as a resource file makes life a lot easier in (re)using your native_script.
The important bits here are that we're pointing to our gdnlib file so Godot knows which dynamic library contains our native_script, and the ``class_name`` which identifies the native_script in our plugin we want to use.
This is a standard Godot resource; you could just create it directly
in of your scene, but saving it to a file makes it much easier to reuse it
in other places. This resource points to our gdnlib file, so that Godot
can know which dynamic library contains our NativeScript. It also defines
the ``class_name`` which identifies the NativeScript in our plugin
we want to use.
Ok, we're all setup. Time to jump back into Godot. We load up the main scene we created way back in the beginning and now we add a Sprite to our scene:
Time to jump back into Godot. We load up the main scene we created way back
in the beginning and now add a Sprite to our scene:
.. image:: img/gdnative_cpp_nodes.png
We're going to assign our Godot logo to this sprite as our texture, turn off centered, and drag our ``gdexample.gdns`` file onto the script property of our sprite:
We're going to assign the Godot logo to this sprite as our texture,
disable the ``centered`` property and drag our ``gdexample.gdns`` file
onto the ``script`` property of the sprite:
.. image:: img/gdnative_cpp_sprite.png
And we're ready to run our project:
We're finally ready to run the project:
.. image:: img/gdnative_cpp_animated.gif
Next steps
----------
Obviously the above is a very basic example just to get you setup but we hope it shows the basics. You can build upon this example to create full fledged scripts to control the nodes in Godot but using C++ as the language.
You should be able to edit and recompile your plugin while the Godot editor remains open and just rerun the project.
The above is only a simple example, but we hope it shows you the basics.
You can build upon this example to create full-fledged scripts to control
nodes in Godot using C++.
You should be able to edit and recompile the plugin while the Godot editor
remains open; just rerun the project after the library has finished building.