The main game scene

Now it's time to bring everything we did together into a playable game scene.

Create a new scene and add a Node named Main. (The reason we are using Node instead of Node2D is because this node will be a container for handling game logic. It does not require 2D functionality itself.)

Click the Instance button (represented by a chain link icon) and select your saved Player.tscn.

Now, add the following nodes as children of Main, and name them as shown (values are in seconds):

• Timer (named MobTimer) - to control how often mobs spawn

• Timer (named ScoreTimer) - to increment the score every second

• Timer (named StartTimer) - to give a delay before starting

• Position2D (named StartPosition) - to indicate the player's start position

Set the Wait Time property of each of the Timer nodes as follows:

• MobTimer: 0.5

• ScoreTimer: 1

• StartTimer: 2

In addition, set the One Shot property of StartTimer to "On" and set Position of the StartPosition node to (240, 450).

Spawning mobs

The Main node will be spawning new mobs, and we want them to appear at a random location on the edge of the screen. Add a Path2D node named MobPath as a child of Main. When you select Path2D, you will see some new buttons at the top of the editor:

Select the middle one ("Add Point") and draw the path by clicking to add the points at the corners shown. To have the points snap to the grid, make sure "Use Grid Snap" and "Use Snap" are both selected. These options can be found to the left of the "Lock" button, appearing as a magnet next to some dots and intersecting lines, respectively.

Important

Draw the path in clockwise order, or your mobs will spawn pointing outwards instead of inwards!

After placing point 4 in the image, click the "Close Curve" button and your curve will be complete.

Now that the path is defined, add a PathFollow2D node as a child of MobPath and name it MobSpawnLocation. This node will automatically rotate and follow the path as it moves, so we can use it to select a random position and direction along the path.

Your scene should look like this:

Main script

Add a script to Main. At the top of the script, we use export (PackedScene) to allow us to choose the Mob scene we want to instance.

GDScriptC#C++

extends Node

export(PackedScene) var mob_scene
var score

We also add a call to randomize() here so that the random number generator generates different random numbers each time the game is run:

GDScriptC#C++

func _ready():
    randomize()

Click the Main node and you will see the Mob Scene property in the Inspector under "Script Variables".

You can assign this property's value in two ways:

• Drag Mob.tscn from the "FileSystem" dock and drop it in the Mob Scene property.

• Click the down arrow next to "[empty]" and choose "Load". Select Mob.tscn.

Next, select the Player node in the Scene dock, and access the Node dock on the sidebar. Make sure to have the Signals tab selected in the Node dock.

You should see a list of the signals for the Player node. Find and double-click the hit signal in the list (or right-click it and select "Connect..."). This will open the signal connection dialog. We want to make a new function named game_over, which will handle what needs to happen when a game ends. Type "game_over" in the "Receiver Method" box at the bottom of the signal connection dialog and click "Connect". Add the following code to the new function, as well as a new_game function that will set everything up for a new game:

GDScriptC#C++

func game_over():
    $ScoreTimer.stop()
    $MobTimer.stop()

func new_game():
    score = 0
    $Player.start($StartPosition.position)
    $StartTimer.start()

Now connect the timeout() signal of each of the Timer nodes (StartTimer, ScoreTimer , and MobTimer) to the main script. StartTimer will start the other two timers. ScoreTimer will increment the score by 1.

GDScriptC#C++

func _on_ScoreTimer_timeout():
    score += 1

func _on_StartTimer_timeout():
    $MobTimer.start()
    $ScoreTimer.start()

In _on_MobTimer_timeout(), we will create a mob instance, pick a random starting location along the Path2D, and set the mob in motion. The PathFollow2D node will automatically rotate as it follows the path, so we will use that to select the mob's direction as well as its position. When we spawn a mob, we'll pick a random value between 150.0 and 250.0 for how fast each mob will move (it would be boring if they were all moving at the same speed).

Note that a new instance must be added to the scene using add_child().

GDScriptC#C++

func _on_MobTimer_timeout():
    # Create a new instance of the Mob scene.
    var mob = mob_scene.instance()

    # Choose a random location on Path2D.
    var mob_spawn_location = get_node("MobPath/MobSpawnLocation")
    mob_spawn_location.offset = randi()

    # Set the mob's direction perpendicular to the path direction.
    var direction = mob_spawn_location.rotation + PI / 2

    # Set the mob's position to a random location.
    mob.position = mob_spawn_location.position

    # Add some randomness to the direction.
    direction += rand_range(-PI / 4, PI / 4)
    mob.rotation = direction

    # Choose the velocity for the mob.
    var velocity = Vector2(rand_range(150.0, 250.0), 0.0)
    mob.linear_velocity = velocity.rotated(direction)

    # Spawn the mob by adding it to the Main scene.
    add_child(mob)

Important

Why PI? In functions requiring angles, Redot uses radians, not degrees. Pi represents a half turn in radians, about 3.1415 (there is also TAU which is equal to 2 * PI). If you're more comfortable working with degrees, you'll need to use the deg2rad() and rad2deg() functions to convert between the two.

Testing the scene

Let's test the scene to make sure everything is working. Add this new_game call to _ready():

GDScriptC#C++

func _ready():
    randomize()
    new_game()

Let's also assign Main as our "Main Scene" - the one that runs automatically when the game launches. Press the "Play" button and select Main.tscn when prompted.

Tip

If you had already set another scene as the "Main Scene", you can right click Main.tscn in the FileSystem dock and select "Set As Main Scene".

You should be able to move the player around, see mobs spawning, and see the player disappear when hit by a mob.

When you're sure everything is working, remove the call to new_game() from _ready().

What's our game lacking? Some user interface. In the next lesson, we'll add a title screen and display the player's score.