Godot Addon Development

res://
└── addons/
    └── my_plugin/
        ├── plugin.cfg          # required — plugin metadata
        ├── plugin.gd           # main EditorPlugin script (named in plugin.cfg)
        ├── my_inspector.gd     # optional — EditorInspectorPlugin
        ├── my_dock.tscn        # optional — dock panel scene
        └── icons/
            └── my_node.svg     # optional — custom node icons

@tool
extends Sprite2D

# Engine.is_editor_hint() is true when running inside the editor,
# false during a running game. Use it to guard editor-only logic.
func _process(delta: float) -> void:
    if Engine.is_editor_hint():
        # This block runs in the editor viewport — safe to call editor APIs.
        update_configuration_warnings()
    else:
        # Normal game logic here.
        pass


# _get_configuration_warnings() returns an array of strings shown as
# yellow warning icons on the node in the Scene panel.
func _get_configuration_warnings() -> PackedStringArray:
    var warnings := PackedStringArray()
    if texture == null:
        warnings.append("Texture is not set. Assign a Texture2D in the Inspector.")
    return warnings

#if TOOLS
using Godot;

[Tool]
public partial class MyToolSprite : Sprite2D
{
    public override void _Process(double delta)
    {
        if (Engine.IsEditorHint())
        {
            // Editor-only logic — safe to call editor APIs here.
            UpdateConfigurationWarnings();
        }
        else
        {
            // Normal game logic.
        }
    }

    public override string[] _GetConfigurationWarnings()
    {
        if (Texture == null)
            return new[] { "Texture is not set. Assign a Texture2D in the Inspector." };
        return System.Array.Empty<string>();
    }
}
#endif

# plugin.gd
@tool
extends EditorPlugin


func _enter_tree() -> void:
    # Register a custom node type. The editor shows MyNode in the
    # "Add Node" dialog under the chosen base class, with a custom icon.
    add_custom_type(
        "MyNode",                              # name shown in editor
        "Node2D",                              # base class to extend
        preload("res://addons/my_plugin/my_node.gd"),
        preload("res://addons/my_plugin/icons/my_node.svg")
    )

    # Add a menu item to the Project menu (top toolbar).
    add_tool_menu_item("My Plugin Action", _on_tool_menu_item)


func _exit_tree() -> void:
    remove_custom_type("MyNode")
    remove_tool_menu_item("My Plugin Action")


func _on_tool_menu_item() -> void:
    print("My Plugin Action triggered")

// Plugin.cs
#if TOOLS
using Godot;

[Tool]
public partial class MyPlugin : EditorPlugin
{
    public override void _EnterTree()
    {
        AddCustomType(
            "MyNode",
            "Node2D",
            GD.Load<Script>("res://addons/my_plugin/MyNode.cs"),
            GD.Load<Texture2D>("res://addons/my_plugin/icons/my_node.svg")
        );

        AddToolMenuItem("My Plugin Action", new Callable(this, MethodName.OnToolMenuAction));
    }

    public override void _ExitTree()
    {
        RemoveCustomType("MyNode");
        RemoveToolMenuItem("My Plugin Action");
    }

    private void OnToolMenuAction()
    {
        GD.Print("My Plugin Action triggered");
    }
}
#endif

func _run_pre_build_check() -> void:
    var unsaved_scenes := EditorInterface.get_unsaved_scenes()  # PackedStringArray of scene paths
    var script_editor := EditorInterface.get_script_editor()
    var unsaved_files := script_editor.get_unsaved_files()      # PackedStringArray of script paths
    if not unsaved_scenes.is_empty() or not unsaved_files.is_empty():
        push_warning("Unsaved work detected — save before building.")

    script_editor.save_all_scripts()   # saves every open script
    script_editor.reload_open_files()  # re-read files changed outside the editor
    # Closes the tab, discarding unsaved changes; OK or ERR_FILE_NOT_FOUND.
    var err := script_editor.close_file("res://addons/my_plugin/generated.gd")

#if TOOLS
private void RunPreBuildCheck()
{
    string[] unsavedScenes = EditorInterface.Singleton.GetUnsavedScenes();
    var scriptEditor = EditorInterface.Singleton.GetScriptEditor();
    string[] unsavedFiles = scriptEditor.GetUnsavedFiles();
    if (unsavedScenes.Length > 0 || unsavedFiles.Length > 0)
        GD.PushWarning("Unsaved work detected — save before building.");

    scriptEditor.SaveAllScripts();
    scriptEditor.ReloadOpenFiles();
    Error err = scriptEditor.CloseFile("res://addons/my_plugin/Generated.cs");
}
#endif