Making main screen plugins

What this tutorial covers

As seen in the Making plugins page, making a basic plugin that extends the editor is fairly easy. This plugin mechanism also allows you to create new UIs in the central part of the editor, similarly to the basic 2D, 3D, Script and AssetLib views. Such editor plugins are referred as “Main screen plugins”.

This tutorial leads you through the creation of a basic main screen plugin. With this plugin example, we want to demonstrate:

  • Creating a main screen plugin
  • Linking the main screen to another plugin GUI element (such as a Tab panel, similar to the Inspector tab)

For the sake of simplicity, the two GUI elements of our main screen plugin will both consist in a Label and a Button. Pressing one element’s button will display some text on the other’s label node.

Initializing the plugin

The plugin itself is a Godot project. It is best to set its contents in an addons/my_plugin_name/ structure. The only files that lie in the root folder are the project.godot file, and the project icon.

In the addons/my_plugin_name/ folder, we create the plugin.cfg file as described in the Making plugins page.

[plugin]
name="Main screen plugin demo"
description="A plugin that adds a main screen panel and a side-panel which communicate with each other."
author="Your Name Here"
version="1.0.0"
script="main_screen_plugin.gd"

We also initialize the file targeted by the script= property of the .cfg file. In our example, main_screen_plugin.gd.

tool
extends EditorPlugin

func _enter_tree():
   pass

func _exit_tree():
   pass

func has_main_screen():
   return true

func make_visible(visible):
   pass

func get_plugin_name():
   return "Main Screen Plugin"

The important part in this script is the has_main_screen() function, which is overloaded so it returns true. This function is automatically called by the editor on plugin activation, to tell it that this plugin adds a new center view to the editor. For now, we’ll leave this script as-is and we’ll come back to it later.

Cenas

The main_screen_plugin.gd file will be responsible for each of our plugin’s UI element instantiation, and it will also manage the communication between them.

As a matter of fact, we wish to design each UI element in their own scene. Different scenes are not aware of each other unless they are both children of a parent scene, yet they will then require get_node("../brother") accessors. Such practice is more likely to produce errors at runtime, especially if these scenes do not share the same parent node. This is why, they should only be allowed to access their children.

So, in order to communicate information to another scene, the best design is to define signals. If a user action in a UI scene #1 has to trigger something in another UI scene #2, then this user action has to emit a signal from scene #1, and scene #2 will be connected to that signal. Since all of our UI scenes will be instanced by main_screen_plugin.gd script, this one script will also connect each of them to the required signals.

Nota

If the main_screen_plugin.gd instantiates the UI scenes, won’t they be brothers nodes then?

Not necessarily: this script may add all UI scenes as children of the same node of the editor’s scene tree - but maybe it won’t. And the main_screen_plugin.gd script will not be the parent node of any instantiated scene because it is a script, not a node! This script will only hold references to instantiated scenes.

Main screen scene

Create a new scene with a Panel root node. Select this root node and, in the viewport, click the Layout menu and select Full Rect. The panel now uses all the space available in the viewport. Now, let’s add a new script on the root node. Name it main_panel.gd.

We then add 2 children to this Panel node: first a Button node. Place it anywhere on the Panel.

Now we need to define a behaviour when this button is pressed. This is covered by the Handling a signal page, so this part will not be described in details in this tutorial. Select the Button node and click the Node side dock. Select the pressed() signal and click the Connect button (you can also double-click the pressed() signal instead). In the window that opened, select the Panel node (we will centralize all behaviors in its attached script). Keep the default function name, make sure that the Make function toggle is ON and hit Connect. This creates an on_Button_pressed() function in the main_panel.gd script, that will be called every time the button is pressed.

As the button gets pressed, we want the side-panel’s Label node to show a specific text. As explained above, we cannot directly access the target scene, so we’ll emit a signal instead. The main_screen_plugin.gd script will then connect this signal to the target scene. Let’s continue in the main_panel.gd script:

tool
extends Panel

signal main_button_pressed(value)

func on_Button_pressed():
   emit_signal("main_button_pressed", "Hello from main screen!")

In the same way, this main scene’s Label node has to show a value when it receives a specific signal. Let’s create a new _on_side_button_pressed(text_to_show) function for this purpose:

func _on_side_button_pressed(text_to_show):
   $Label.text = text_to_show

We are done for the main screen panel. Save the scene as main_panel.tscn.

Tabbed panel scene

The tabbed panel scene is almost identical to the main panel scene. You can either duplicate the main_panel.tscn file and name the new file side_panel.tscn, or re-create it from a new scene by following the previous section again. However, you will have to create a new script and attach it to the Panel root node. Save it as side_panel.gd. Its content is slightly different, as the signal emitted and the target function have different names. Here is the script’s full content:

tool
extends Panel

signal side_button_pressed(value)

func on_Button_pressed():
   emit_signal("side_button_pressed", "Hello from side panel!")

func _on_main_button_pressed(text_to_show):
   $Label.text = text_to_show

Connecting the two scenes in the plugin script

We now need to update the main_screen_plugin.gd script so the plugin instances our 2 GUI scenes and places them at the right places in the editor. Here is the full main.gd:

tool
extends EditorPlugin

const MainPanel = preload("res://addons/my_plugin_name/main_panel.tscn")
const SidePanel = preload("res://addons/my_plugin_name/side_panel.tscn")

var main_panel_instance
var side_panel_instance

func _enter_tree():
   main_panel_instance = MainPanel.instance()
   side_panel_instance = SidePanel.instance()

   # Add the main panel to the editor's main viewport.
   get_editor_interface().get_editor_viewport().add_child(main_panel_instance)

   # Add the side panel to the Upper Left (UL) dock slot of the left part of the editor.
   # The editor has 4 dock slots (UL, UR, BL, BR) on each side (left/right) of the main screen.
   add_control_to_dock(DOCK_SLOT_LEFT_UL, side_panel_instance)

   # Hide the main panel
   make_visible(false)

func _exit_tree():
   main_panel_instance.queue_free()
   side_panel_instance.queue_free()

func _ready():
   main_panel_instance.connect("main_button_pressed", side_panel_instance, "_on_main_button_pressed")
   side_panel_instance.connect("side_button_pressed", main_panel_instance, "_on_side_button_pressed")

func has_main_screen():
   return true

func make_visible(visible):
   if visible:
      main_panel_instance.show()
   else:
      main_panel_instance.hide()

func get_plugin_name():
   return "Main Screen Plugin"

A couple of specific lines were added. First, we defined the constants that contain our 2 GUI packed scenes (MainPanel and SidePanel). We will use these resources to instance both scenes.

The _enter_tree() function is called before _ready(). This is where we actually instance the 2 GUI scenes, and add them as children of specific parts of the editor. The side panel case is similar to the example shown in Making plugins page: we add the scene in an editor dock. We specified it will be placed in the left-side dock, upper-left tab.

EditorPlugin class does not provide any function to add an element in the main viewport. We thus have to use the get_editor_interface().get_editor_viewport() to obtain this viewport and add our main panel instance as a child to it. We call the make_visible(false) function to hide the main panel so it is not directly shown when first activating the plugin.

The _exit_tree() is pretty straightforward. It is automatically called when the plugin is deactivated. It is then important to queue_free() the elements previously instanced to preserve memory. If you don’t, the elements will effectively be invisible in the editor, but they will remain present in the memory. Multiple de-activations/re-activations will then increase memory usage without any way to free it, which is not good.

Finally the make_visible() function is overridden to hide or show the main panel as needed. This function is automatically called by the editor when the user clicks on another main viewport button such as 2D, 3D or Script.

Try the plugin

Activate the plugin in the Project Settings. You’ll observe a new button next to 2D, 3D, Script above the main viewport. You’ll also notice a new tab in the left dock. Try to click the buttons in both side and main panels: events are emitted and caught by the corresponding target scene to change the Label caption inside it.