Introduce simplified event handler function overrides

[Naros]

Description

Orchestrator presently is directly tied to the GDScript-based interface where implementation of input callbacks relies on overriding particular Godot virtual functions like _gui_input, _unhandled_input, and _unhandled_key_input. These callbacks provide the user with a reference to a specific InputEvent object that requires the called function to inspect the object and determine precisely what action to take, i.e.:

void _gui_input(const Ref<InputEvent>& p_event) {
  Ref<InputMouseButtonEvent> mb = p_event;
  if (mb.is_valid() && mb->is_pressed() && mb->get_button_index() == MOUSE_BUTTON_LEFT) {
    // perform action
  }
}

There are a couple of ways that Orchestrator could provide an abstraction to Godot's input system.

Custom node

The easiest solution is to build a custom node that takes the Ref<InputEvent> and decodes it to a series of various output flow pins based on type, additionally outputting multiple attributes about the event such as the keycode, position, pressed state, and the mouse button involved. Internally, this node is a glorified branch and type-cast abstraction.

Macro

Another relatively easy solution would be to delay this until we have the macro subsystem in play and then add a macro that effectively abstracts this behavior much in the same way as a C++ custom node would work.

Bake into the script binding

A more radical idea would be to bake this abstraction into the OScriptInstance implementation. For example, there could be a series of functions that are designed for each input event type, providing direct access to some common attributes for each event type such as mouse position, pressed/unpressed, keycode, etc. Then in OScriptInstance when the script is converted to a DAG, the instance checks whether such nodes are present and if so, wires up a Godot delegation.

For example, let's say there is this type of specialized function signature:

void _input_key_event(const Ref<InputKeyEvent>& p_event, bool p_pressed, const KeyCode p_code);

The OScriptInstance would then redirect all _gui_input, _unhandled_input, and _unhandled_key_input calls that refer to a key-based input to this specialized event node type. This reduces the need for the user to cast the event type before working with the event type.

Implementation ideas

No response