path: root/blog/src/g/gogodot_jam3_devlog_1.md

title: Creating my Go Godot Jam 3 entry devlog 1
author: David Luévano
lang: en
summary: Details on the implementation for the game I created for the Go Godot Jam 3, which theme is Evolution.
tags: gamedev
	godot
	gamejam
	english

**IF YOU'RE SEEING THIS, THIS IS A WIP**

The jam's theme is Evolution and all the details are listed [here](https://itch.io/jam/go-godot-jam-3). 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](https://blog.luevano.xyz/g/flappybird_godot_devlog_1.html) clone I developed, I'm using the directory structure I wrote about on [Godot project structure](https://blog.luevano.xyz/g/godot_project_structure.html) 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](https://github.com/bram-dingelstad/godot-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](https://www.gdquest.com/docs/guidelines/best-practices/godot-gdscript/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](https://www.aseprite.org/), 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:

![FileSystem - Snake dir structure](images/g/gogodot_jam3/file_system_snake_dir_structure.png "FileSystem - Snake dir structure")

### 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:

```gdscript
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:

![Snake - Basic movement (left and right controls)](images/g/gogodot_jam3/snake_basic_movement.gif "Snake - Basic movement (left and right controls)")

### 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`:

```gdscript
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:

```gdscript
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:

![Snake - Basic movement with path](images/g/gogodot_jam3/snake_basic_movement_with_path.gif "Snake - Basic movement with path")

### 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:

```gdscript
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:

```gdscript
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:

![Snake - Basic movement with all body parts](images/g/gogodot_jam3/snake_basic_movement_added_body_parts.gif "Snake - Basic movement with all body parts")

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:

```gdscript
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:

```gdscript
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:

```gdscript
# 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:

![Snake - Basic movement with dynamic addition of new segments](images/g/gogodot_jam3/snake_basic_movement_with_dynamic_segments.gif "Snake - Basic movement with dynamic addition of new segments")

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:

```gdscript
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:

```gdscript
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:

```gdscript
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:

```gdscript
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:

![Snake - Food basic interaction](images/g/gogodot_jam3/snake_food_basic_interaction.gif "Snake - Food basic interaction")


## From here on just minor temp notes for now

- Added restartability function.
- Added signals for game control: `game_over` and `game_start`.
- Tried fixing the snake because it keeps getting closer to the first body node because of accuarcy of the path when doing curves (the more the snake rotates, the more this is affected).
	- Added signal `snake_rotated`
- Fixed issue where the curve2d stayed the same even when restarting.
- Disabled drawing of the curve2d.
- Added world generation by implementing a "random walker" by following [Nuclear Throne Like Map Generation In Godot](https://www.youtube.com/watch?v=ppP2Doq3p7s), with minor changes to fit my needs and implemented few other things.
	- Added several signals for the world gen: `world_gen_walker_started(id)`, `world_gen_walker_finished(id)`, `world_gen_walker_died(id)` and `world_gen_spawn_walker_unit(location)`.
- Edited the food manager to communicate with the world gen to get actual possible tile locations.
	- Added a location attribute to food.
	- Added several related signals: `food_placing_new_food(type)`, `food_placed_new_food(type, location)` and `food_eaten(type, location)`.
- Tweaked the tracking of the snake size.
- Tweaked the food system to contain more attributes and use a base food node.
- Added a HUD with mini snake sprites. Added necessary signals.
- Added a HUD for growth progress. Added necessary signals.
- Refactored the nodes to make it work with `change_scene_to`, and added a main menu.
- Added GUI for dead screen, showing the progress. Will add next mutations there.
- Added new food and generalized a bit the food system.

## 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?