Cleaned up and refactored some code

src/Filesystem.gd

@@ -0,0 +1,59 @@
+extends Node
+
+@onready var shader: Shader = load("res://src/shader/template.gdshader")
+var original_image: ImageTexture
+var result: Image
+
+var cwd = "."
+var last_image_savepath = ""
+var last_shader_savepath = ""
+var last_original_image_path = ""
+
+func get_absolute_path(p: String) -> String:
+	# this only works on Linux!
+	if !p.begins_with("/"):
+		return self.cwd + "/" + p.lstrip("./")
+	return p
+
+func load_original_image(path: String):
+	print("Load ", path)
+	var img = Image.new()
+	var err = img.load(path)
+	if err == OK:
+		original_image = ImageTexture.create_from_image(img)
+		if path != self.last_original_image_path:
+			self.last_original_image_path = path
+		if self.last_image_savepath == "":
+			self.last_image_savepath = path
+	else:
+		print("An error occured!")
+
+func load_image(path: String) -> ImageTexture:
+	print("Load ", path)
+	return ImageTexture.create_from_image(Image.load_from_file(path))
+
+func save_result(path: String):
+	print("Export ", path)
+	var err = self.result.save_png(path)
+	if err != OK:
+		print("An error occured!")
+	else:
+		self.last_image_savepath = path
+
+func load_shader(path: String):
+	print("Load ", path)
+	var file = FileAccess.open(path, FileAccess.READ)
+	var shader_code = file.get_as_text()
+	self.shader = Shader.new()
+	shader.code = shader_code
+	if "/" in path: # update current working directory
+		self.cwd = path.substr(0, path.rfind("/"))
+	self.last_shader_savepath = path
+
+func save_shader(path: String, content: String):
+	print("Save ", path)
+	var file = FileAccess.open(path, FileAccess.WRITE)
+	file.store_string(content)
+	if "/" in path: # update current working directory
+		self.cwd = path.substr(0, path.rfind("/"))
+	self.last_shader_savepath = path