[godot] Additive mix blending bug after track entries completed

[Reltdeats]

See https://esotericsoftware.com/forum/d/24802-godot-additive-mix-blending-bug-after-track-entries-completed

[Reltdeats]

To facilitate testing this bug, I replicated the additive blendig demo. Attach this code to the oficial Owl spine ( SpineSprite node ) and uncomment lines 22 to 25 to replicate the error.

extends SpineSprite

@export_range(0.0,10.0) var blend_speed = 5.0

@onready var state = get_animation_state()
@onready var left = state.set_animation('right', true, 2)
@onready var right = state.set_animation('left', true, 3)
@onready var up = state.set_animation('up', true, 4)
@onready var down = state.set_animation('down', true, 5)

var mouse_pos = Vector2.ZERO
var left_alpha =  0.0
var right_alpha =  0.0
var up_alpha =  0.0
var down_alpha =  0.0

# Called when the node enters the scene tree for the first time.
func _ready():
	state.set_animation("idle", true, 0)
	state.set_animation("blink", true, 1)
	
	# left.set_mix_blend(SpineConstant.MixBlend_Add)
	# right.set_mix_blend(SpineConstant.MixBlend_Add)
	# up.set_mix_blend(SpineConstant.MixBlend_Add)
	# down.set_mix_blend(SpineConstant.MixBlend_Add)
	
	left.set_alpha(0.0)
	right.set_alpha(0.0)
	up.set_alpha(0.0)
	down.set_alpha(0.0)
	
func _input(event):
	if event is InputEventMouseMotion:
		mouse_pos = event.position
	else:
		mouse_pos = get_viewport_rect().size / 2
		
# Called every frame. 'delta' is the elapsed time since the previous frame.
func _process(delta):
	calculate_blend(mouse_pos.x, mouse_pos.y, delta)
	
func calculate_blend(x, y, delta):
	var size = get_viewport_rect().size
	var center = size / 2
	
	var left_pos = 1 - x / center.x if x < center.x else 0.0;
	var right_pos = (x - center.x) / (size.x - center.x) if x > center.x else 0.0;
	var up_pos = 1 - y / center.y if y < center.y else 0.0;
	var down_pos = (y - center.y) / (size.y - center.y) if y > center.y else 0.0;
	
	
	left_alpha = lerp(left_alpha, left_pos, delta * blend_speed)
	right_alpha = lerp(right_alpha, right_pos, delta * blend_speed)
	up_alpha = lerp(up_alpha, up_pos, delta * blend_speed)
	down_alpha = lerp(down_alpha, down_pos, delta * blend_speed)
	
	left.set_alpha(left_alpha)
	right.set_alpha(right_alpha)
	up.set_alpha(up_alpha)
	down.set_alpha(down_alpha)

[badlogic]

Cheers!