pandemonium-cpp

This repository contains the C++ bindings for the Pandemonium Engine's GDNative API.

• Versioning
• Contributing
• Getting Started
• Creating a simple class

Versioning

This repositories follows the same branch versioning as the main Pandemonium Engine repository:

• master tracks the current development branch.
• 3.x tracks the development of the next 3.x minor release.
• Other versioned branches (e.g. 3.3, 3.2) track the latest stable release in the corresponding branch.

Stable releases are also tagged on this repository: Tags.

For any project built against a stable release of Pandemonium, we recommend using this repository as a Git submodule, checking out the specific tag matching your Pandemonium version.

As the master and 3.x branches are constantly getting updates, if you are using pandemonium-cpp against a more current version of Pandemonium, see the instructions in pandemonium_headers for updating the relevant files.

Contributing

We greatly appreciate help in maintaining and extending this project. If you wish to help out, ensure you have an account on GitHub and create a "fork" of this repository. Rémi "Akien" Verschelde wrote an excellent bit of documentation for the main Pandemonium project on this: Pull request workflow

Please install clang-format and copy the files in misc/hooks into .git/hooks so formatting is done before your changes are submitted.

Getting Started

Build latest version of Pandemonium	GitHub	Docs

Setting up a new project

We recommend using Git for managing your project. The instructions below assume you're using Git. Alternatively, you can download the source code directly from GitHub. In this case, you need to download both pandemonium-cpp and pandemonium_headers.

mkdir SimpleLibrary
cd SimpleLibrary
mkdir bin
mkdir src
git clone --recursive https://github.com/pandemoniumengine/pandemonium-cpp

If you wish to use a specific branch, add the -b option to the clone command:

git clone --recursive https://github.com/pandemoniumengine/pandemonium-cpp -b 3.0

If your project is an existing repository, use a Git submodule instead:

git submodule add https://github.com/pandemoniumengine/pandemonium-cpp
git submodule update --init --recursive

Right now, our directory structure should look like this:

SimpleLibrary/
├─pandemonium-cpp/
| └─pandemonium_headers/
├─bin/
└─src/

Updating the api.json file

Our api.json file contains metadata for all the classes that are part of the Pandemonium core. This metadata is required to generate the C++ binding classes for use in GDNative modules.

This file is supplied with our pandemonium_headers repository for your convenience. However, if you're running a custom build of Pandemonium and need access to classes that have recent changes, you must generate a new api.json file. You do this by starting your Pandemonium executable with the following parameters:

pandemonium --gdnative-generate-json-api api.json

Now copy the api.json file into your folder structure to make it easier to access.

See the remark below for the extra custom_api_file SCons argument, which is required to tell SCons where to find your file.

Compiling the C++ bindings library

The final step is to compile our C++ bindings library:

cd pandemonium-cpp
scons platform=<your platform> generate_bindings=yes
cd ..

Replace <your platform> with either windows, linux, osx or android. If you leave out platform, the target platform will automatically be detected from the host platform.

The resulting library will be created in pandemonium-cpp/bin/, take note of its name as it'll differ depending on the target platform.

Compiling for Android

Download the latest Android NDK and set the NDK path.

scons platform=android generate_bindings=yes ANDROID_NDK_ROOT="/PATH-TO-ANDROID-NDK/" android_arch=<arch>

The value of android_arch can be armv7, arm64v8, x86, x86_64. Most Android devices in use nowadays use an ARM architecture, so compiling for armv7 and arm64v8 is often enough when distributing an application.

ANDROID_NDK_ROOT can also be set in the environment variables of your PC if you don't want to include it in your SCons call.

Compilation options

You can optionally add the following options to the SCons command line:

• When targeting Linux, add use_llvm=yes to use Clang instead of GCC.
• When targeting Windows, add use_mingw=yes to use MinGW instead of MSVC.
• When targeting Windows, include target=runtime to build a runtime build.
• To use an alternative api.json file, add use_custom_api_file=yes custom_api_file=../api.json. Be sure to specify the correct location where you placed your file (it can be a relative or absolute path).

Creating a simple class

Create init.cpp under SimpleLibrary/src/ and add the following code:

#include <pandemonium.h>
#include <Reference.h>



class SimpleClass : public Reference {
    GDCLASS(SimpleClass, Reference);
public:
    SimpleClass() { }

    /** `_init` must exist as it is called by Pandemonium. */
    void _init() { }

    void test_void_method() {
        Pandemonium::print("This is test");
    }

    Variant method(Variant arg) {
        Variant ret;
        ret = arg;

        return ret;
    }

    static void _register_methods() {
        register_method("method", &SimpleClass::method);

        /**
         * The line below is equivalent to the following GDScript export:
         *     export var _name = "SimpleClass"
         **/
        register_property<SimpleClass, String>("base/name", &SimpleClass::_name, String("SimpleClass"));

        /** Alternatively, with getter and setter methods: */
        register_property<SimpleClass, int>("base/value", &SimpleClass::set_value, &SimpleClass::get_value, 0);

        /** Registering a signal: **/
        // register_signal<SimpleClass>("signal_name");
        // register_signal<SimpleClass>("signal_name", "string_argument", PANDEMONIUM_VARIANT_TYPE_STRING)
    }

    String _name;
    int _value;

    void set_value(int p_value) {
        _value = p_value;
    }

    int get_value() const {
        return _value;
    }
};

/** GDNative Initialize **/
extern "C" void GDN_EXPORT pandemonium_gdnative_init(pandemonium_gdnative_init_options *o) {
    Pandemonium::gdnative_init(o);
}

/** GDNative Terminate **/
extern "C" void GDN_EXPORT pandemonium_gdnative_terminate(pandemonium_gdnative_terminate_options *o) {
    Pandemonium::gdnative_terminate(o);
}

/** NativeScript Initialize **/
extern "C" void GDN_EXPORT pandemonium_nativescript_init(void *handle) {
    Pandemonium::nativescript_init(handle);

    Pandemonium::register_class<SimpleClass>();
}

Compiling the GDNative library

Once you've compiled the GDNative C++ bindings (see above), you can compile the GDNative library we've just created.

Linux

cd SimpleLibrary
clang++ -fPIC -o src/init.o -c src/init.cpp -g -O3 -std=c++14 -Ipandemonium-cpp/include -Ipandemonium-cpp/include/core -Ipandemonium-cpp/include/gen -Ipandemonium-cpp/pandemonium_headers
clang++ -o bin/libtest.so -shared src/init.o -Lpandemonium-cpp/bin -l<name of the pandemonium-cpp>

You'll need to replace <name of the pandemonium-cpp> with the file that was created in Compiling the cpp bindings library.

This creates the file libtest.so in your SimpleLibrary/bin directory.

Windows

cd SimpleLibrary
cl /Fosrc/init.obj /c src/init.cpp /nologo -EHsc -DNDEBUG /MDd /Ipandemonium-cpp\include /Ipandemonium-cpp\include\core /Ipandemonium-cpp\include\gen /Ipandemonium-cpp\pandemonium_headers
link /nologo /dll /out:bin\libtest.dll /implib:bin\libsimple.lib src\init.obj pandemonium-cpp\bin\<name of the pandemonium-cpp>

You'll need to replace <name of the pandemonium-cpp> with the file that was created in Compiling the cpp bindingslibrary. Replace /MDd with /MD to create a release build, which will run faster and be smaller.

This creates the file libtest.dll in your SimpleLibrary/bin directory.

macOS

For macOS, you'll need to find out which compiler flags need to be used. These are likely similar to Linux when using Clang, but may not be identical.

If you find suitable compiler flags for this example library, feel free to submit a pull request 🙂

Android

cd SimpleLibrary
aarch64-linux-android29-clang++ -fPIC -o src/init.o -c src/init.cpp -g -O3 -std=c++14 -Ipandemonium-cpp/include -Ipandemonium-cpp/include/core -Ipandemonium-cpp/include/gen -Ipandemonium-cpp/pandemonium_headers
aarch64-linux-android29-clang++ -o bin/libtest.so -shared src/init.o -Lpandemonium-cpp/bin -l<name of the pandemonium-cpp>

You'll need to replace <name of the pandemonium-cpp> with the file that was created in Compiling the cpp bindings library. The command above targets arm64v8. To target armv7, use armv7a-linux-androideabi29-clang++ instead of aarch64-linux-android29-clang++.

This creates the file libtest.so in your SimpleLibrary/bin directory.

iOS

GDNative isn't supported on iOS yet. This is because iOS only allows linking static libraries, not dynamic libraries. In theory, it would be possible to link a GDNative library statically, but some of GDNative's convenience would be lost in the process as one would have to recompile the engine on every change. See issue #30 in the Pandemonium headers repository for more information.

HTML5

GDNative is supported on specific exports for the HTML5 platform since Pandemonium 3.3. Linking webassembly modules is currently underspecified in the standard, but emscripten, which Pandemonium uses to build the HTML5 version, implements its own linking system.

To build GDNative libraries, you will need a recent version of Emscripten.

cd SimpleLibrary
emcc  -o bin/libtest.wasm -g -O3 -s SIDE_MODULE=1 src/init.cpp pandemonium-cpp/bin/<name of the pandemonium-cpp> -Ipandemonium-cpp/include -Ipandemonium-cpp/include/core -Ipandemonium-cpp/include/gen -Ipandemonium-cpp/pandemonium_headers

You'll need to replace <name of the pandemonium-cpp> with the file that was created in Compiling the cpp bindings library.

This creates the file libtest.so in your SimpleLibrary/bin directory.

Creating .gdnlib and .gdns files

Follow the instructions in pandemonium_headers/README.md to create the .gdns file. This file contains paths to GDNative libraries for various platforms. This makes the library usable from Pandemonium in a platform-independent manner.

Implementing with GDScript

Once your GDNative library is compiled and referenced in a .gdns file, you can use it in GDScript or C#. Here's an example with GDScript:

var simpleclass = load("res://simpleclass.gdns").new()
simpleclass.method("Test argument")

Using Pandemonium classes in C++

Pandemonium expects you to manage its classes the same way the engine does. These rules apply to all Pandemonium classes, including your NativeScripts, but not to any normal C++ classes used in your library.

• Instantiate Objects using _new(), not C++'s new operator.

Sprite *sprite = Sprite::_new();

• Destroy Nodes using queue_free(), not C++'s delete operator.

some_old_node->queue_free();

• Wrap References in Ref instead of passing around raw pointers. They are reference-counted and don't need to be freed manually.

Ref<Texture> texture = resource_loader->load("res://icon.png");

• Pass core types that do not inherit Object by value. The containers (Array, Dictionary, PoolArray, String) manage their own memory and do not need to be explicitly initialized or freed.

Array ints;
ints.append(123);
return ints;

• Initialize your NativeScript classes in their _init() method, not their constructor. The constructor can't access the base class's methods.

• Cast objects using Object::cast_to, not unsafe C-style casts or static_cast.

MeshInstance *m = Object::cast_to<MeshInstance>(get_node("ChildNode"));
// `m` will be null if it's not a MeshInstance
if (m) { ... }

• Never use Pandemonium types in static or global variables. The Pandemonium API isn't loaded until after their constructors are called.

String s; // crashes
class SomeClass {
    static Dictionary d; // crashes

    static Node *node_a = NULL; // fine, it's just a pointer
    static Node *node_b = Node::_new(); // crashes
};