Mouse trail

extends Node

const MAX_POINTS: int = 110
const MIN_STEP: float = 7.0
const DRIFT_SPEED: float = 1.1

var trail: Line2D
var head: Polygon2D
var pointer: Vector2
var center: Vector2
var span: Vector2
var drifting: bool = true
var elapsed: float = 0.0


func _ready() -> void:
	_add_background()

	var view: Vector2 = get_viewport().get_visible_rect().size
	center = view * 0.5
	span = view * 0.32
	pointer = center

	var gradient: Gradient = Gradient.new()
	gradient.set_color(0, Color('#8da5f3', 0.0))
	gradient.set_color(1, Color('#8eef97'))

	var taper: Curve = Curve.new()
	taper.add_point(Vector2(0.0, 0.05))
	taper.add_point(Vector2(1.0, 1.0))

	trail = Line2D.new()
	trail.width = 16.0
	trail.width_curve = taper
	trail.gradient = gradient
	trail.joint_mode = Line2D.LINE_JOINT_ROUND
	trail.begin_cap_mode = Line2D.LINE_CAP_ROUND
	trail.end_cap_mode = Line2D.LINE_CAP_ROUND
	add_child(trail)

	head = _make_circle(10.0, Color('#f3d48d'))
	head.position = pointer
	add_child(head)

	_add_label('one point per frame, the oldest point leaves once the line is full', Vector2(40, 40))

	print('move the mouse, the line keeps the last ' + str(MAX_POINTS) + ' points')


func _input(event: InputEvent) -> void:
	if event is InputEventMouseMotion:
		pointer = event.position
		drifting = false


func _process(delta: float) -> void:
	elapsed += delta

	if drifting:
		pointer = center + Vector2(cos(elapsed * DRIFT_SPEED), sin(elapsed * DRIFT_SPEED * 1.6)) * span

	head.position = pointer

	if trail.get_point_count() == 0 or trail.points[-1].distance_to(pointer) > MIN_STEP:
		trail.add_point(pointer)

	while trail.get_point_count() > MAX_POINTS:
		trail.remove_point(0)


func _add_label(text: String, at: Vector2) -> void:
	var label: Label = Label.new()
	label.text = text
	label.position = at
	label.add_theme_color_override('font_color', Color('#999999'))
	label.add_theme_font_size_override('font_size', 20)
	add_child(label)


func _make_circle(radius: float, color: Color) -> Polygon2D:
	var points: PackedVector2Array = PackedVector2Array()

	for i in 24:
		points.append(Vector2(cos(TAU * i / 24.0), sin(TAU * i / 24.0)) * radius)

	var circle: Polygon2D = Polygon2D.new()
	circle.polygon = points
	circle.color = color

	return circle


func _add_background() -> void:
	var background: ColorRect = ColorRect.new()
	background.color = Color('#12141a')
	add_child(background)
	background.set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)