extends Node2D

@onready var sim_viewport := $SubViewport
@onready var display_sprite := $Sprite2D

var tex_a: Texture2D
var tex_b: Texture2D
var swap = false

func _ready():
	# Create textures
	tex_a = ImageTexture.create_from_image(
		Image.create(sim_viewport.size.x, sim_viewport.size.y, false, Image.FORMAT_RGBAF)
	)
	tex_b = tex_a.duplicate()
	
	# Assign one texture to the simulation shader as input
	$SubViewport/ColorRect.material.set("shader_parameter/trail_tex", tex_a)
	display_sprite.texture = tex_a

func _process(_delta):
	# Swap textures each frame
	swap = !swap
	var src = tex_a if swap else tex_b
	var dst = tex_b if swap else tex_a
	
	# Assign src as input and dst as render target
	$SubViewport/ColorRect.material.set("shader_parameter/trail_tex", src)
	sim_viewport.render_target_update_mode = SubViewport.UPDATE_ALWAYS
	display_sprite.texture = dst