Creating my Go Godot Jam 3 entry devlog 1

IF YOU’RE SEEING THIS, THIS IS A WIP

The jam’s theme is Evolution and all the details are listed here. This time I’m logging as I go, so there might be some changes to the script or scenes along the way. Note that I’m not going to go into much details, the obvious will be ommitted.

I wanted to do a Snake clone, and I’m using this jam as an excuse to do it and add something to it. The features include:

• Snakes will pass their stats in some form to the next snakes.
• Non-grid snake movement. I just hate the grid constraint, so I wanted to make it move in any direction.
• Depending on the food you eat, you’ll gain new mutations and the more you eat the more that mutation develops.
• Procedural map creation.

Initial setup

Again, similar to the FlappyBird clone I developed, I’m using the directory structure I wrote about on Godot project structure with slight modifications to test things out. Also using similar Project settings as those from the FlappyBird clone like the pixel art texture imports, keybindings, layers, etc..

I’ve also setup GifMaker, with slight modifications as the AssetLib doesn’t install it correctly and contains unnecessry stuff: moved necessary files to the res://addons directory, deleted test scenes and files in general, and copied the license to the res://docs directory. Setting this up was a bit annoying because the tutorial it’s bad (with all due respect). I might do a separate entry just to explain how to set it up, because I couldn’t find it anywhere other than by inspecting some of the code/scenes.

This time I’m also going to be using an Event bus singleton (which I’m going to just call Event) as managing signals was pretty annoying on my last project; as well as a Global singleton for essential stuff so I don’t have to do as many cross references between nodes/scenes.

Assets

This time I’ll be creating my own assets in Aseprite, wont be that good, but enough to prototype and get things going.

The snake

This is the most challenging part in my opinion as making all the body parts follow the head in a user defined path it’s kinda hard. I tried with like 4-5 options and the one I’m detailing here is the only one that worked as I wanted for me. This time the directory structure I’m using is the following:

Basic movement

The most basic thing is to move the head, this is what we have control of. Create a scene called Head.tscn and setup the basic KinematicBody2D with it’s own Sprite and CollisionShape2D (I used a small circle for the tip of the head), and set the Collision Layer/Mask accordingly, for now just layer = bit 1. And all we need to do, is keep moving the snake forwards and be able to rotate left or right. Created a new script called head.gd attached to the root (KinematicBody2D) and added:

extends KinematicBody2D

enum {
    LEFT=-1,
    RIGHT=1
}

var velocity: Vector2 = Vector2.ZERO
var _direction: Vector2 = Vector2.UP


func _physics_process(delta: float) -> void:
    if Input.is_action_pressed("move_left"):
        _rotate_to(LEFT)
    if Input.is_action_pressed("move_right"):
        _rotate_to(RIGHT)

    velocity = _direction * Global.SNAKE_SPEED

    velocity = move_and_slide(velocity)
    _handle_time_elapsed(delta)


func _rotate_to(direction: int) -> void:
    rotate(deg2rad(direction * Global.SNAKE_ROT_SPEED * get_physics_process_delta_time()))
    _direction = _direction.rotated(deg2rad(direction * Global.SNAKE_ROT_SPEED * get_physics_process_delta_time()))

After tunning all the necessary parameters you should get something like this:

Setting up path following

To move other snake parts by following the snake head the only solution I found was to use the Path2D and PathFollow2D nodes. Path2D basically just handles the curve/path that PathFollow2D will use to move its child node; and I say “child node” in singular… as PathFollow2D can only handle one damn child, all the other ones will have weird transformations and/or rotations. So, the next thing to do is to setup a way to compute (and draw so we can validate) the snake’s path/curve.

Added the signal snake_path_new_point(coordinates) to the Event singleton and then add the following to head.gd:

var _time_elapsed: float = 0.0

# using a timer is not recommended for < 0.01
func _handle_time_elapsed(delta: float) -> void:
    if _time_elapsed >= Global.SNAKE_POSITION_UPDATE_INTERVAL:
        Event.emit_signal("snake_path_new_point", global_position)
        _time_elapsed = 0.0
    _time_elapsed += delta

This will be pinging the current snake head position every 0.01 seconds (defined in Global). Now create a new scene called Snake.tscn which will contain a Node2D, a Path2D and an instance of Head as its childs. Create a new script called snake.gd attached to the root (Node2D) with the following content:

class_name Snake
extends Node2D

onready var path: Path2D = $Path

func _ready():
    Event.connect("snake_path_new_point", self, "_on_Head_snake_path_new_point")


func _draw() -> void:
    if path.curve.get_baked_points().size() >= 2:
        draw_polyline(path.curve.get_baked_points(), Color.aquamarine, 1, true)


func _on_Head_snake_path_new_point(coordinates: Vector2) -> void:
    path.curve.add_point(coordinates)
    # update call is to draw curve as there are new points to the path's curve
    update()

With this, we’re now populating the Path2D curve points with the position of the snake head. You should be able to see it because of the _draw call. If you run it you should see something like this:

Define body parts for the snake

At this point the only thing to do is to add the corresponding next body parts and tail of the snake. To do so, we need a PathFollow2D to use the live-generating Path2D, the only caveat is that we need one of these per body part/tail (this took me hours to figure out, thanks documentation).

Create a new scene called Body.tscn with a PathFollow2D as its root and an Area2D as its child, then just add the necessary Sprite and CollisionShap2D for the Area2D, I’m using layer = bit 2 for its collision. Create a new script called generic_segment.gd with the following code:

extends PathFollow2D

export(String, "body", "tail") var TYPE: String = "body"


func _physics_process(delta: float) -> void:
    offset += Global.SNAKE_SPEED * delta

And this can be attached to the Body‘s root node (PathFollow2D), no extra setup needed. Repeat the same steps for creating the Tail.tscn scene and when attaching the generic_segment.gd script just configure the Type parameter to tail in the GUI (by selecting the node with the script attached and editing in the Inspector).

Adding body parts

Now it’s just a matter of handling when to add new body parts in the snake.gd script. For now I’ve only setup for adding body parts to fulfill the initial length of the snake (this doesn’t include the head or tail). The extra code needed is the following:

export(PackedScene) var BODY_SEGMENT_NP: PackedScene
export(PackedScene) var TAIL_SEGMENT_NP: PackedScene

var current_body_segments: int = 0
var max_body_segments: int = 1


func _add_initial_segment(type: PackedScene) -> void:
    if path.curve.get_baked_length() >= (current_body_segments + 1.0) * Global.SNAKE_SEGMENT_SIZE:
        var _temp_body_segment: PathFollow2D = type.instance()
        path.add_child(_temp_body_segment)
        current_body_segments += 1


func _on_Head_snake_path_new_point(coordinates: Vector2) -> void:
    path.curve.add_point(coordinates)
    # update call is to draw curve as there are new points to the path's curve
    update()

    # add the following lines
    if current_body_segments < max_body_segments:
        _add_initial_segment(BODY_SEGMENT_NP)
    elif current_body_segments == max_body_segments:
        _add_initial_segment(TAIL_SEGMENT_NP)

Select the Snake node and add the Body and Tail scene to the parameters, respectively. Then when running you should see something like this:

Now, we need to handle adding body parts after the snake is complete and already moved for a bit, this will require a queue so we can add part by part in the case that we eat multiple pieces of food in a short period of time. For this we need to add some signals: snake_adding_new_segment(type), snake_added_new_segment(type), snake_added_initial_segments and use them when makes sense. Now we need to add the following:

var body_segment_stack: Array
var tail_segment: PathFollow2D
# didn't konw how to name this, basically holds the current path lenght
#   whenever the add body segment, and we use this stack to add body parts
var body_segment_queue: Array

As well as updating _add_initial_segment with the following so it adds the new segment on the specific variable:

if _temp_body_segment.TYPE == "body":
    body_segment_stack.append(_temp_body_segment)
else:
    tail_segment = _temp_body_segment

Now that it’s just a matter of creating the segment queue whenever a new segment is needed, as well as adding each segment in a loop whenever we have items in the queue and it’s a good distance to place the segment on. These two things can be achieved with the following code:

# this will be called in _physics_process
func _add_new_segment() -> void:
    var _path_length_threshold: float = body_segment_queue[0] + Global.SNAKE_SEGMENT_SIZE
    if path.curve.get_baked_length() >= _path_length_threshold:
        var _removed_from_queue: float = body_segment_queue.pop_front()
        var _temp_body_segment: PathFollow2D = BODY_SEGMENT_NP.instance()
        var _new_body_offset: float = body_segment_stack.back().offset - Global.SNAKE_SEGMENT_SIZE

        _temp_body_segment.offset = _new_body_offset
        body_segment_stack.append(_temp_body_segment)
        path.add_child(_temp_body_segment)
        tail_segment.offset = body_segment_stack.back().offset - Global.SNAKE_SEGMENT_SIZE

        current_body_segments += 1


func _add_segment_to_queue() -> void:
    # need to have the queues in a fixed separation, else if the eating functionality
    #   gets spammed, all next bodyparts will be spawned almost at the same spot
    if body_segment_queue.size() == 0:
        body_segment_queue.append(path.curve.get_baked_length())
    else:
        body_segment_queue.append(body_segment_queue.back() + Global.SNAKE_SEGMENT_SIZE)

With everything implemented and connected accordingly then we can add segments on demand (for testing I’m adding with a keystroke), it should look like this:

For now, this should be enough, I’ll add more stuff as needed as I go. Last thing is that after finished testing that the movement felt ok, I just added a way to stop the snake whenever it collides with itself by using the following code (and the signal snake_segment_body_entered(body)) in a main.gd script that is the entry point for the game:

func _snake_disabled(on_off: bool) -> void:
    _snake.propagate_call("set_process", [on_off])
    _snake.propagate_call("set_process_internal", [on_off])
    _snake.propagate_call("set_physics_process", [on_off])
    _snake.propagate_call("set_physics_process_internal", [on_off])
    _snake.propagate_call("set_process_input", [on_off])

Which will stop the snake node and all children.

The food

For now I just decided to setup a simple system to see everything works fine. The idea is to make some kind of generic food node/scene and a “food manager” to spawn them, for now in totally random locations. For this I added the following signals: food_placing_new_food(type), food_placed_new_food(type) and food_eaten(type).

First thing is creating the Food.tscn which is just an Area2D with its necessary children with an attached script called food.gd. The script is really simple:

class_name Food # needed to access Type enum outside of the script, this registers this script as a node
extends Area2D

enum Type {
    APPLE
}

var _type_texture: Dictionary = {
    Type.APPLE: preload("res://entities/food/sprites/apple.png")
}

export(Type) var TYPE
onready var _sprite: Sprite = $Sprite


func _ready():
    connect("body_entered", self, "_on_body_entered")
    _sprite.texture = _type_texture[TYPE]


func _on_body_entered(body: Node) -> void:
    Event.emit_signal("food_eaten", TYPE)
    queue_free()

Then this food_eaten signal is received in snake.gd to add a new segment to the queue.

Finally, for the food manager I just created a FoodManager.tscn with a Node2D with an attached script called food_manager.gd. To get a random position:

func _get_random_pos() -> Vector2:
    var screen_size: Vector2 = get_viewport().get_visible_rect().size
    var temp_x: float = randf() * screen_size.x - screen_size.x / 2.0
    var temp_y: float = randf() * screen_size.y - screen_size.y / 2.0

    return Vector2(temp_x, temp_y)

Which gets the job done, but later I’ll have to add a way to check that the position is valid. And to actually place the food:

func _place_new_food() -> void:
    var food: Area2D = FOOD.instance()
    var position: Vector2 = _get_random_pos()
    food.global_position = position
    add_child(food)

And this is used in _process to place new food whenever needed. For now I added a condition to add food until 10 pieces are in place, and keep adding whenever the food is is lower than 10. After setting everything up, this is the result:

Brainstorm/To-do

• Snake clone with evolution.

  • Evolution on the snake itself?
    • Evolve after eating X amount?
    • Evolve after eating X type of food?
      • Similar to Contra, where you can switch the food (not sure if this counts as evolution)
  • Evolution on the world?
    • Start with a small procedural generated map, then expand it?
  • When snake dies, it passes the genes it collected by eating some food to the next snakes?
    • Or similar to the Rogue Legacy system?

• Snake clone

  • Each snake has several attributes
    • Health
    • Time to live (before getting food?)
  • Special food will unlock new attributes for subsequent snakes
    • Jumping ability (need to level it up by eating more of the same food or by using it)
    • Crawl up walls?

Resources

• Nuclear Throne Like Map Generation In Godot