Object class

General definition

Object is the base class for almost everything. Most classes in Godot inherit directly or indirectly from it. Objects provide reflection and editable properties, and declaring them is a matter of using a single macro like this.

class CustomObject : public Object {

    GDCLASS(CustomObject, Object); // this is required to inherit
};

This makes Objects gain a lot of functionality, like for example

obj = memnew(CustomObject);
print_line("Object class: ", obj->get_class()); // print object class

obj2 = obj->cast_to<OtherClass>(); // converting between classes, this also works without RTTI enabled.

References:

Registering an Object

ClassDB is a static class that holds the entire list of registered classes that inherit from Object, as well as dynamic bindings to all their methods properties and integer constants.

Classes are registered by calling:

ClassDB::register_class<MyCustomClass>()

Registering it will allow the class to be instanced by scripts, code, or creating them again when deserializing.

Registering as virtual is the same but it can’t be instanced.

ClassDB::register_virtual_class<MyCustomClass>()

Object-derived classes can override the static function static void _bind_methods(). When one class is registered, this static function is called to register all the object methods, properties, constants, etc. It’s only called once. If an Object derived class is instanced but has not been registered, it will be registered as virtual automatically.

Inside _bind_methods, there are a couple of things that can be done. Registering functions is one:

ClassDB::register_method(D_METHOD("methodname", "arg1name", "arg2name"), &MyCustomMethod);

Default values for arguments can be passed in reverse order:

ClassDB::register_method(D_METHOD("methodname", "arg1name", "arg2name"), &MyCustomType::method, DEFVAL(-1)); // default value for arg2name

D_METHOD is a macro that converts “methodname” to a StringName for more efficiency. Argument names are used for introspection, but when compiling on release, the macro ignores them, so the strings are unused and optimized away.

Check _bind_methods of Control or Object for more examples.

If just adding modules and functionality that is not expected to be documented as thoroughly, the D_METHOD() macro can safely be ignored and a string passing the name can be passed for brevity.

References:

Constants

Classes often have enums such as:

enum SomeMode {
   MODE_FIRST,
   MODE_SECOND
};

For these to work when binding to methods, the enum must be declared convertible to int, for this a macro is provided:

VARIANT_ENUM_CAST(MyClass::SomeMode); // now functions that take SomeMode can be bound.

The constants can also be bound inside _bind_methods, by using:

BIND_CONSTANT(MODE_FIRST);
BIND_CONSTANT(MODE_SECOND);

Properties (set/get)

Objects export properties, properties are useful for the following:

  • Serializing and deserializing the object.
  • Creating a list of editable values for the Object derived class.

Properties are usually defined by the PropertyInfo() class. Usually constructed as:

PropertyInfo(type, name, hint, hint_string, usage_flags)

For example:

PropertyInfo(Variant::INT, "amount", PROPERTY_HINT_RANGE, "0,49,1", PROPERTY_USAGE_EDITOR)

This is an integer property, named “amount”, hint is a range, range goes from 0 to 49 in steps of 1 (integers). It is only usable for the editor (edit value visually) but won’t be serialized.

Another example:

PropertyInfo(Variant::STRING, "modes", PROPERTY_HINT_ENUM, "Enabled,Disabled,Turbo")

This is a string property, can take any string but the editor will only allow the defined hint ones. Since no usage flags were specified, the default ones are PROPERTY_USAGE_STORAGE and PROPERTY_USAGE_EDITOR.

There are plenty of hints and usage flags available in object.h, give them a check.

Properties can also work like C# properties and be accessed from script using indexing, but this usage is generally discouraged, as using functions is preferred for legibility. Many properties are also bound with categories, such as “animation/frame” which also make indexing impossible unless using operator [].

From _bind_methods(), properties can be created and bound as long as set/get functions exist. Example:

ADD_PROPERTY(PropertyInfo(Variant::INT, "amount"), "set_amount", "get_amount")

This creates the property using the setter and the getter.

Binding properties using _set/_get/_get_property_list

An additional method of creating properties exists when more flexibility is desired (i.e. adding or removing properties on context).

The following functions can be overridden in an Object derived class, they are NOT virtual, DO NOT make them virtual, they are called for every override and the previous ones are not invalidated (multilevel call).

void _get_property_info(List<PropertyInfo> *r_props); // return list of properties
bool _get(const StringName &p_property, Variant &r_value) const; // return true if property was found
bool _set(const StringName &p_property, const Variant &p_value); // return true if property was found

This is also a little less efficient since p_property must be compared against the desired names in serial order.

Dynamic casting

Godot provides dynamic casting between Object-derived classes, for example:

void somefunc(Object *some_obj) {

     Button *button = some_obj->cast_to<Button>();
}

If cast fails, NULL is returned. This system uses RTTI, but it also works fine (although a bit slower) when RTTI is disabled. This is useful on platforms where a very small binary size is ideal, such as HTML5 or consoles (with low memory footprint).

Signals

Objects can have a set of signals defined (similar to Delegates in other languages). Connecting to them is rather easy:

obj->connect(<signal>, target_instance, target_method)
// for example:
obj->connect("enter_tree", this, "_node_entered_tree")

The method _node_entered_tree must be registered to the class using ClassDB::register_method (explained before).

Adding signals to a class is done in _bind_methods, using the ADD_SIGNAL macro, for example:

ADD_SIGNAL(MethodInfo("been_killed"))

References

Reference inherits from Object and holds a reference count. It is the base for reference counted object types. Declaring them must be done using Ref<> template. For example:

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

Ref<MyReference> myref(memnew(MyReference));

myref is reference counted. It will be freed when no more Ref<> templates point to it.

References:

Resources:

Resource inherits from Reference, so all resources are reference counted. Resources can optionally contain a path, which reference a file on disk. This can be set with resource.set_path(path). This is normally done by the resource loader though. No two different resources can have the same path, attempt to do so will result in an error.

Resources without a path are fine too.

References:

Resource loading

Resources can be loaded with the ResourceLoader API, like this:

Ref<Resource> res = ResourceLoader::load("res://someresource.res")

If a reference to that resource has been loaded previously and is in memory, the resource loader will return that reference. This means that there can be only one resource loaded from a file referenced on disk at the same time.

  • resourceinteractiveloader (TODO)

Resource saving

Saving a resource can be done with the resource saver API:

ResourceSaver::save("res://someresource.res", instance)

Instance will be saved. Sub resources that have a path to a file will be saved as a reference to that resource. Sub resources without a path will be bundled with the saved resource and assigned sub-IDs, like “res://someresource.res::1”. This also helps to cache them when loaded.