extends Control

var viewport: Viewport
var render_queue: Array  # of PoolByteArrays
var result_queue: Array  # of PoolByteArrays
var current_image: Image
var current_tex: ImageTexture  # Needed to prevent GC before draw
var waiting_for_viewport: bool
var done_first_draw: bool

func _ready() -> void:
	self.viewport = get_parent()
	self.render_queue = []
	self.result_queue = []
	self.waiting_for_viewport = false
	self.done_first_draw = false
	self.current_image = Image.new()
	self.current_tex = ImageTexture.new()

func _process(_delta) -> void:
	update()

func _draw() -> void:
	# Seems like the first one always fails
	if not self.done_first_draw:
		self.done_first_draw = true
		return

	if self.waiting_for_viewport:
		# Another node later in the draw sequence can call this within the same frame,
		# otherwise, this picks it up the following frame
		get_result()

	if not self.render_queue:
		return

	# Draw the next ImageTexture
	var data: PoolByteArray = self.render_queue.pop_front()
	print(data.subarray(0, 15))
	self.current_image.create_from_data(4096, 4096, false, Image.FORMAT_LA8, data)
	self.current_tex.create_from_image(self.current_image, Texture.FLAG_FILTER)
	self.material.set_shader_param('tex', self.current_tex)
	draw_texture(self.current_tex, Vector2.ZERO)
	self.waiting_for_viewport = true  # Grab the result next draw

func get_result() -> void:
	var result_texture := self.viewport.get_texture()
	var result_image := result_texture.get_data()
	var result_bytes := result_image.get_data()

	# Debugging: compare a sequence of all the possible 16bit integers
	print_debug('result_image format is %d and has size'%result_image.get_format(), result_image.get_size(), result_bytes.subarray(0, 11))
	test_readback(result_bytes)

	self.result_queue.append(result_bytes)
	self.waiting_for_viewport = false

func test_readback(result_bytes: PoolByteArray):
	# Debugging: compare a sequence of all the possible 16bit integers
	var buff := StreamPeerBuffer.new()
	buff.set_data_array(result_bytes)
	var tex_readback = 0
	var uv_readback = 0
	for i in 0x1000:
		tex_readback = buff.get_u16()
		uv_readback = buff.get_u16()
		if tex_readback != i:
			print('tex readback %d (0x%04x) was instead %d (0x%04x)'%[i, i, tex_readback, tex_readback])
		if uv_readback != i:
			print('uv readback %d (0x%04x) was instead %d (0x%04x)'%[i, i, uv_readback, uv_readback])