How to bind a c++ virtual method to gdscript

octod · January 10, 2024, 2:58pm

Edit 4.3.x

Since 4.3.x you can create your virtual methods. These are the steps:

In the header file, include those headers:

#include <godot_cpp/core/binder_common.hpp>
#include <godot_cpp/core/gdvirtual.gen.inc>

Now define you virtual method in the class’ declaration. Note, there are many macros to do it, example:

/// if the macro ends with the "RC" suffix, the virtual method will returns a value, 
/// which is the first argument of the macro, followed by the virtual name method 
/// and the arguments expected by the macro name itself
GDVIRTUAL1RC(float, _my_virtual_method_name, Array);
/// if the macro does not end with that suffix, then the first
GDVIRTUAL2(_another_virtual_method_name, Array, double);

Then into your implementation, inside the static method _bind_methods, use these macros

GDVIRTUAL_BIND(_my_virtual_method_name, "argument_0_name")
GDVIRTUAL_BIND(_another_virtual_method_name, "argument_0_name", "argument_1_name")

Godot Version

4.2.x

Question

Hello, I am porting my extension to c++ and I need to mark several functions as virtuals in gdscript.

What I tried

I tried using the BIND_VIRTUAL_METHOD but it does not mark my method as virtual in gdscript.

If I try to create an empty method in the header file called for example _foo, then bind it in the static method _bind_methods as

BIND_VIRTUAL_METHOD(MyClass, _foo)

it does not appear in the methods listed by gdscript.

Could somebody give me a hint? Thanks in advance

coder · January 10, 2024, 4:42pm

These issues are related. They all seem to mention using call instead.

github.com/godotengine/godot

BIND_VIRTUAL_METHOD in GDextensions doesn't create a virtual function in GDscript

opened 09:11PM - 24 Sep 23 UTC

TrickyFatCat

bug topic:gdextension

### Godot version 4.1.1 ### System information Pop!_OS 22.04 ### Iss…ue description Using `BIND_VIRTUAL_METHOD` script in `_bind_methods()` doesn't create a virtual function in GDScript. ### Steps to reproduce 1. Create simple GDextension 2. Build it 3. Add to the project ```C++ //MyClass.h #ifndef MYCLASS_H #define MYCLASS_H #include <godot_cpp/classes/node.hpp> namespace godot{ class MyClass : public Node{ GDCLASS(MyClass, Node) protected: static void _bind_methods(); void foo(); }; } #endif //MyClass.cpp #include "my_class.h" #include <godot_cpp/core/class_db.hpp> #include <godot_cpp/variant/variant.hpp> using namespace godot; void MyClass::_bind_methods(){ BIND_VIRTUAL_METHOD(MyClass, foo); } void MyClass::foo(){ } ``` After building the extension, you can `MyClass` in the editor. However, you can't override `foo()` function as GDscript doesn't see it and it isn't shown in documentation section. ### Minimal reproduction project N/A

github.com/godotengine/godot-cpp

Virtual function binding

opened 03:34PM - 04 Aug 23 UTC

Kehom

### Godot version 4.1 stable ### godot-cpp version 4.1 stable ### Sy…stem information Windows 10 and Linux Mint ### Issue description When binding a virtual function in a custom class, things become rather *finicky*. For the purposes of explanation I will exemplify things using `Resource` as base class, but this behavior occurs with any other base. Suppose I have this: ``` class CustomResource : public Resource { .... static void _bind_methods() { BIND_VIRTUAL_METHOD(CustomResource, perform_task); } ... virtual void perform_task() { some_default_behavior... } }; ``` When in GDScript, if I attempt to directly call that virtual function with `some_instance.perform_task()` I will get an error telling that the function does not exist. Yet, If I do `some_instance.call("perform_task")` then the function will be called and the default behavior will occur. I can then create a derived class in GDScript and override `perform_task()` without any problem. In that case either `.perform_task()` or `call("perform_task")` will work in GDScript. Now, from the C++ code: 1 - If I directly call `->perform_task()`, then the default behavior will occur. If I create a derived class in C++ and override that virtual function, then I will get the overridden code. However if I override that function in a GDScript class then I will still get the C++ default behavior. 2 - If I call the function with `->call("perform_task")` I will be able to override that function from GDScript but not in a C++ class. The workaround that I'm currently using is something like this: ``` class CustomResource : public Resource { ... static void _bind_methods() { BIND_VIRTUAL_METHOD(CustomResource, _perform_task); ClassDB::bind_method(D_METHOD("perform_task"), &CustomResource::perform_task); } ... virtual void _perform_task() { some_default_behavior... } void perform_task() { call("_perform_task"); } }; ``` This does present the intuitive `.perform_task()` way of calling the function from GDScript and `->perform-task()` from C++. However there are problems here. 1 - Using `call()` does not work in a const function. Well, not without some *"hacky"* code (casting the `this` into a non cost version). 2 - In a C++ derived class I need to do this: ``` class SpecialCustomResource : public CustomResource { ... static void _bind_methods() { ClassDB::bind_method(D_METHOD("_perform_task"), &SpecialCustomResource::_perform_task); } ... virtual void _perform_task() override { some_other_behavior... } }; ``` If I don't bind the overridden function as a normal one then the `call()` will not find the desired function. Another thing that occurs when the function is not registered is that if you are expecting a return value `nullptr` will be the result. Is the described intended behavior? ### Steps to reproduce The entire explanation is, in a way, steps to reproduce the problem. ### Minimal reproduction project I don't have one in hand. If really absolutely necessary I can work on one

octod · January 11, 2024, 8:40am

Ok, so as a TLDR, it is not possible at the moment without using ugly and fragile workarounds.

Thank you!

coder · January 14, 2024, 5:45pm

Yes. BIND_VIRTUAL_METHOD only seems to be used in the godot_cpp bindings and I believe it’s very different from what the engine uses to expose the methods like _ready and _process. If you’re a module developer, you may have more to work with than with GDExtension.

octod · March 21, 2024, 3:02pm

2024-03-21 Update

In Godot 4.3 there will be a new ClassDB method called add_virtual_method

The signature is simple:

static void godot::ClassDB::add_virtual_method(const godot::StringName &p_class, const godot::MethodInfo &p_method, const godot::Vector<godot::StringName> &p_arg_names = godot::Vector<godot::StringName>())

If you need to expose virtuals which can be called from your code, this is the way.

octod · September 4, 2024, 9:54am

Edit 4.3.x

Since 4.3.x you can create your virtual methods. These are the steps:

In the header file, include those headers:

#include <godot_cpp/core/binder_common.hpp>
#include <godot_cpp/core/gdvirtual.gen.inc>

Now define you virtual method in the class’ declaration. Note, there are many macros to do it, example:

/// if the macro ends with the "RC" suffix, the virtual method will returns a value, 
/// which is the first argument of the macro, followed by the virtual name method 
/// and the arguments expected by the macro name itself
GDVIRTUAL1RC(float, _my_virtual_method_name, Array);
/// if the macro does not end with that suffix, then the first
GDVIRTUAL2(_another_virtual_method_name, Array, double);

system · October 4, 2024, 9:55am

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