Save and load game data in Godot


Posted on May 29, 2020

In this tutorial, we will create simple save and load functionality for our Godot game.

Implementing this feature early on in the game development cycle can save you a lot of pain further down the line it also forces you to think about how data is structured and managed in your game. All good things to be thinking about.

I’ll be using Godot 3.2.1 for this tutorial and writing the code in GDScript. We aren’t using any features in the engine that are likely to change, so if you’re on an earlier or later version the code should still work. I’ve been using the same code in my games since version 2, without any changes.

We will be structuring our game data using a GDScript dictionary and serializing it to JSON. We will then read the JSON file back and load it into our game data.

Creating a new project

Fire up Godot and create a new project.

New Godot Project

The first thing is to create a ‘Root Node’, for this we will select Other Node, click Node and call it Main.

Add Main Node

To make our game data accessible, we will need to create a script that is autoloaded on startup, I tend to name this global.gd.

Create a folder in the resources tab called Scripts and then create a new Godot script file in that folder by right-clicking and selecting New Script...

Create Singleton Godot Script

Creating our game data

Open the global.gd script and add some dummy game data. This will be a Dictionary type and holds key/value pairs.

extends Node

var game_data = {
	"player": {
		"name": "Super Mario",
		"coins": 10
	}
}

We create a simple player key, which will hold our player data, in this case, a name and a number of coins.

Next, we will need to make this file autoload so that it can be accessed anywhere from within our game. Click Project -> Project Settings and select the AutoLoad tab. Click the folder icon next to Path and select the global.gd file from our scripts folder.

The node name will pre-populate with Global. Click the Add button to add it and then click Close.

Create Singleton Godot Script

We just created a singleton node, only one instance of this will exist during runtime, so if a script changes the data, it is changed for all. With this approach we can show the coin count on the screen and as soon as a coin is collected and the data changes, the label will update automatically.

Save Function

Lets create a new function called save_game in our globals script.

func save_game():
	var file = File.new()
	var location = "user://save_game.sav"

	print("Saving game to: " + OS.get_user_data_dir())
	if file.open(location, File.WRITE) != 0:
		print("Cannot write save file to " + location)
	else:
		file.store_line(to_json(game_data))
		file.close()

In this function, we create a new File object, assign a location to save the file. We then check if we can write to the location that we assigned, printing out an error if not. If the location is writeable we serialize our game_data into JSON and write it to the file using the store_line method. Finally, we close the file.

The location of the user:// path differs depending on the platform. For Windows, this usually exists within APPDATA and for Linux/Mac it is ~/.PROJECT_NAME. I added a print statement so that the location is outputted to the console on save.

Load Function

The load function will open our save game file and populate the data back into a GDScript Dictionary object.

Let’s create a new function called load_save_file.

func load_save_file():
	var file = File.new()
	file.open("user://save_gam.sav", file.READ)
	var text = file.get_as_text()
	game_data = parse_json(text)
	file.close()

We again create a new File object and open the save game file from its location. We read the text from the file and parse the JSON, storing it back in our game_data dictionary. Finally, we close the file.

Save and Load game script for Godot

Rendering our game data

Let’s visualise this a little more, by adding a couple of labels and buttons. Add two labels to the Main scene and name them PlayerName and PlayerCoins. You can add some dummy text, we will be setting this when the game loads.

Add a script to the Main root node we created earlier. Let’s change the _process function, so that it sets the player name and coin labels. This function is called every frame, so when we later modify our save game and load it back in, we will see the labels update.

func _process(delta):
	$PlayerName.text = Global.game_data.player.name
	$PlayerCoins.text = "Coins: " + str(Global.game_data.player.coins)

You will notice that we set the label text with our game data, that is accessible through the singleton node Global that we created.

The str function is casting our coins variable to a string so that it can be appended to the Coins: string. Without it, you will get a type error. We could have stored our coins as a string, but I think it’s good practice to be strict with your types.

Create save and load buttons

Add two buttons to your Main node and name them SaveGame and LoadGame.

Save and Load buttons

We will connect a button_up signal for each button that connects to our Main node. This will automatically create two functions within our Main script.

Click the Node tab and select the button_up signal. Select Main and click the Connect button. Do this for both buttons.

Connect Godot Signal to Node

You should now have two new functions in Main. Let’s now call our save and load functions when the respective buttons are clicked.

func _on_SaveGame_button_up():
	Global.save_game()

func _on_LoadGame_button_up():
	Global.load_save_file()

If you run your game and click the Save Game button you should see the location of the same game file printed out to the console.

--- Debugging process started ---
Godot Engine v3.2.1.stable.custom_build - https://godotengine.org
OpenGL ES 3.0 Renderer: GeForce GTX 1060 6GB/PCIe/SSE2
 
Saving game to: /home/richard/.local/share/godot/app_userdata/SaveAndLoadGame

Whilst the game is still running, open up the save game file from the location that was printed out. Edit the coins value and save, then go back to the game and click Load Game. You should see the coins value automatically update!

Example of save and load game in Godot

Final notes

This approach is very flexible and allows you to better control your game data. There some caveats, however. The Godot dictionary data is held in memory, this usually isn’t a problem, but if you have a game where you’re procedurally generating a lot of data, you’re going to hit some performance issues. I previously worked on a prototype that procedurally generated a city with over a hundred thousand citizens. This occupied a huge amount of memory and I ended up having to write a native extension to handle this, as opposed to using the above approach.

I would also separate the game data from other data that is static, such as weapon names, inventory items and gear. They don’t need to be stored in the save file. Thinking about this separation of data early on in the development cycle is good and will save you from a lot of pain further down the line.

Read more on: godot  gamedev