Initiation à Godot

Define scenes

Defines scenes

Our game will be based on scenes. We already described the advantages of scenes in a Scenes dedicated chapter. Mainly, we can sum up the purpose of the scenes with these characteristics :

Encapsulation: a scene will encapsulate a certain feature or component of your game. All behaviour of that feature will be contained in that scene.
Reusable: scenes will be instanced inside other scenes and contribute to game optimisation as well as reducing production time.
Parameterisable: scenes can have different parameters that are unique for each instance, and affect their behaviour/appareance.
Ease Teamwork: Scenes can be edited by different members of the team, to enable them to integrate their content to the game.

From here we will created a scene for each element our game will need :

a scene for the background
a scene for the player
a scene for each obstacle element type
a scene to mix them all

Create a scene

So let’s create our first scene.

Go to Scene > New Scene menu.This doesn’t change anything in the editor for the scene is empty. In fact, in we try to save it right now, Godot tells us there is no possibility to save an empty scene. So let’s add some elements to it.
In the Scene panel on the right, click the Add/Create a new node or use Ctrl+A. This will show the Create New Node window up.
The list of Node type is quite long so we usually use the search field to get the one we want. Let’s write Node2D which is a basic node type.
Among the displayed results, select the one you need and click create.
You can now save the scene with Scene > Save scene as… Here we save it in a scene folder that we just created.
Let’s name it scene1.scn or level.scn.
Eventually test the scene by clicking the play scene button , the middle on top part of the editor.

The Node2D is now added to the scene and is shown both in 2D editor (main window) and in Scene panel.

Scene can be saved with .scn and .xml extensions. If you want to keep control on the content and do some batch operation, you might prefer the second one. But keep in mind that usually .scn will give better performance at runtime.

Define main scene

But as we said, the game will have many scenes. So there is a need to define with which scene the game will begin.

Go back to the project settings ( Scene > Project Settings…)
In the application category, check the main_scene setting and click the folder icon on the right of it.
Choose the scene of your choice among the scenes you saved.
You can now play the entire game by clicking the play game button . The game will also available from project manager and be played after run button is pressed.

The bat

The Bat is the main character of the scene. It will have a Sprite (or some other visual element), a Camera following it, and a collision area. When defining the Bat scene, we keep in mind the following points :

The Bat will have many parameters to control various aspects of gameplay, such us the speed, the gravity force, the force of the jump. Expose these parameters to allow the Game Designer team to tweak them and test them in the game.
The Bat will have a collision area, which will also be tweaked by the Game Designer team. In the example game we use a Control node, even tho we don't need all the features the Control provides, simply because it provides a simple way to modify a rectangle area inside the editor. Sometimes this is better than using the correct method from the programming point of view; we could use a Rect2 type to define the collision area, but that would be harder to edito for a game desinger.
We define 2 animations, fly and die, and we write code assuming those animations will exist. Remember that animations can control the entire scene, change the sprite for the bat, play sounds, fire off particle systems, show text, etc. This is all up to the artists.

With this in mind, we have a technical sprcification we can provide the team for this scene:

There has to be a Control node, with the name area. The scripts will retrieve the size of this Control, to calculate collision.
There has to be an AnimationPlayer node, with the name animation, and 2 animations called fly and die.
There has to be a Camera node (type: Camera2D), following the bat; set the Limit > Bottom property to e.g. 800 so the camera stops when reaching the ground

These are the only requirements for the scene to work, everything else (including for example, the name and type of the sprite node) is up to the team, and somewhat irrelevant to us. They can add nodes, use different types of nodes, etc. It is up to the team to make it look good, and play balanced, and up to the producer to organize everyone to provide content to the scene.

User interface

The scene for the user interface shows information about the current game, such as the score, lives, player status, etc. In this case, we have just one Label that displays a number, with the current score. The code will look for a node called label and set a number to it.

In this case we use a CanvasLayer node as root, and add a labelcalled pointsas a child. Using CanvasLayer instead of just classic node let’s us define freely the z position of the gui. Viewport is supposed to be placed on 0, but we will also have a parallax background. So let’s set the layer value as 2 and the GUI should always be on top, whatever the scene trees are.

Obstacles

The obstacle scene is spawned by the main level. This scene has 2 damage areas (one in the top, one in the bottom), and a bonus area in the middle. If the player goes over the bonus area, a point is awarded. This scene will be very important to the game designer, because it exposes the parameters used to balance the game (in conjunction with the parameters exposed in the Bat scene). This can be a bit tricky to express, so be prepared to have many discussions with your Game Design team to make sure you can provide them all the options they need. Don't be afraid to provide basic elements, game designers don't need a pretty interface, they need freedom :) And sometimes they know the basics of programming (and sometimes they know a lot of programming, but don't count on this). Give them freedom, and they'll surprise you !

In our example, the Obstacle scene provides the following elements:

A node named top, with the top element. This element has its own damage area, and sprite.
A node named bottom, with the bottom element.
A node named point with the bonus area.
Parameters top_range and bottom_range to control the range of positions where the top and bottom parts will spawn. These values specify 2 numbers, the minimum and maximum position on the Y axis that each part can have when they spawn. The gap between the top and the bottom parts will be the bonus area.

Optimize the workflow by instanciating obstacle scenes

Once your game is working, we can go deeper in the production. It will be time to add objects to our world.

Create a new scene saved as obstacle.scn or bottom.scn (because will need also a top obstacle for clouds) and set it as followed :
Add an area node
Let’s add some art element to our player by using an image file. Select the Sprite node.
In the Inspector, look at the Texture property and click on the list on the right of the label and choose Load to get a file browser in which you will choose the right image.
If you need to define the way this ressource is used, click the > button at the right of the texture preview field, and you’ll get more settings. You will particularly see the filepathandSizeas it is used in our node.
Save the scene.

Now we have made a first element we can add it to our main scene and use it in context.

Open create a scene file that will manage both obstacle position.
Go to Scene tree panel. As new node will be added as child as selected node, select the root node.
Click the + button on top of the window and a pop up will let you choose the obstacle.scn scene.
Once done, it is displayed in the Scene tree and in 2D view. Let’s go on until you get the right tree.
Instantiate this new scene in the main scene or any other scene that will help, and so on until all the logic of the game lead to the main scene.

Instance of obstacles in a specific scene

The Scene panel displays the name of the instance, and at the right, a folder that shows it’s instance and then available script for it. If you right-click on the folder icon, Show Children menu will display its nodes directly from here.

We are now done with instantiation. It really seems like we’ve done a copy-paste but using this method, any changes made to the original bat scene will be applied to instances. In term of team management it helps everyone work on its part at his own rythm, without having other contributors to worry about. On the other way, it is still important to verify is working well after deep changes. In this case, refer to game design documents or scene graph to know which part are affected.

Main Scene

The main scene instances everything together, and in this example serves as the main title screen. The main scene will also receive input and notify every element of events that happen during the game (collision between objects, game was reset, etc). There are many methods to structure your game and the communication between your game elements. Objects can send messages to each other (through method calls or other type of messaging), or they can all send events to a main scene. They can also broadcast their events through signals, that objects connect to, or sending messages to groups. It's up to you to decide, but keep in mind that level designers will want as much freedom as possible to instance objects around the level.

In our example scene, there are 2 animations : game_over and game_reset. These can be used to display/hide a title screen, or show messages to the user. (see chapter Animations to know more about animation factory)

There is also a parameter that controls how often the Obstacle scene spawns, called spawn_distance, which is the distance in pixels between 2 spawned obstacles.

At last we'll add a ParallaxBackground node (with 1:1 scaling).

Add a ParallaxLayer child node.
Set the Motion > Mirroring property to the size of your sprite.
Add a Sprite child node.
Set the Texture property to your background image.