scene manager :)

assets/shaders/test_filter.gdshader

@@ -0,0 +1,15 @@
+shader_type canvas_item;
+
+uniform sampler2D SCREEN_TEXTURE : hint_screen_texture;
+
+vec2 warp(vec2 uv) {
+	return vec2(
+		uv.x + sin(TIME + uv.y * 50.0) * 0.005,
+		uv.y
+	);
+}
+
+void fragment() {
+	vec2 uv = warp(SCREEN_UV);
+	COLOR = texture(SCREEN_TEXTURE, uv);
+}

autoloads/scene_manager.gd

@@ -0,0 +1,88 @@
+extends Node
+
+
+## Methods of scaling the game viewport.
+enum ScaleMode {
+	## Maintain aspect ratio and scale by highest whole number that will fit within the screen.
+	INTEGER,
+	## Maintain aspect ratio and scale to fill at least one axis.
+	ASPECT,
+	## Stretch to fill screen, ignoring aspect ratio.
+	STRETCH,
+}
+
+
+## The [enum ScaleMode] currently in use.
+@export var scale_mode: ScaleMode = ScaleMode.INTEGER
+
+@export_group("Internal References")
+## Viewport the game is rendered in.
+@export var viewport: SubViewport
+## Control that holds the viewport. Resized according to [member scale_mode].
+@export var viewport_holder: Control
+
+
+## Design/native resolution of the game.
+@onready var resolution: Vector2 = Vector2(
+	ProjectSettings.get_setting("display/window/size/viewport_width"),
+	ProjectSettings.get_setting("display/window/size/viewport_height")
+)
+
+
+## The currently active scene.
+##
+## Setting this will remove and free the previously active scene if it exists.
+var current_scene: Node:
+	set(new_scene):
+		# do nothing if already current scene
+		if current_scene == new_scene:
+			return
+		# remove current scene
+		if current_scene:
+			viewport.remove_child(current_scene)
+			current_scene.queue_free()
+		# add new scene
+		if new_scene.is_inside_tree():
+			new_scene.get_parent().remove_child(new_scene)
+		viewport.add_child(new_scene)
+		current_scene = new_scene
+
+
+func _ready() -> void:
+	var tree := get_tree()
+	await tree.process_frame
+	# capture the main scene
+	if tree.current_scene != self:
+		current_scene = tree.current_scene
+		tree.current_scene = self
+	# gather screen_overlay references
+	for child in tree.root.get_children():
+		if child is Control:#and child.is_in_group(&"screen_overlay")
+			child.get_parent().remove_child(child)
+			viewport_holder.add_child(child)
+			child.set_anchors_preset(Control.PRESET_CENTER, false)
+			child.size = resolution
+			child.pivot_offset = resolution * 0.5
+	# set up viewport display
+	viewport.size = resolution
+	viewport_holder.size = resolution
+	viewport_holder.pivot_offset = resolution * 0.5
+	_on_window_size_changed()
+	tree.root.size_changed.connect(_on_window_size_changed)
+
+
+func _on_window_size_changed() -> void:
+	# gather resolution information
+	var screen_size := Vector2(get_tree().root.size)
+	var scale_delta := screen_size / resolution
+	
+	# apply scale mode
+	match scale_mode:
+		ScaleMode.INTEGER:
+			var scale = floorf(minf(scale_delta.x, scale_delta.y))
+			viewport_holder.scale = Vector2(scale, scale)
+		ScaleMode.ASPECT:
+			var scale = minf(scale_delta.x, scale_delta.y)
+			viewport_holder.scale = Vector2(scale, scale)
+		ScaleMode.STRETCH:
+			viewport_holder.scale = scale_delta

autoloads/scene_manager.tscn

@@ -0,0 +1,49 @@
+[gd_scene load_steps=2 format=3 uid="uid://ckgsfhfpg00ys"]
+
+[ext_resource type="Script" path="res://autoloads/scene_manager.gd" id="1_1hxm1"]
+
+[node name="SceneManager" type="Node" node_paths=PackedStringArray("viewport", "viewport_holder")]
+script = ExtResource("1_1hxm1")
+viewport = NodePath("ViewportHolder/ViewportContainer/SubViewport")
+viewport_holder = NodePath("ViewportHolder")
+
+[node name="ClearColor" type="CanvasLayer" parent="."]
+layer = -128
+
+[node name="ColorRect" type="ColorRect" parent="ClearColor"]
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+color = Color(0, 0, 0, 1)
+
+[node name="ViewportHolder" type="Control" parent="."]
+layout_mode = 3
+anchors_preset = 8
+anchor_left = 0.5
+anchor_top = 0.5
+anchor_right = 0.5
+anchor_bottom = 0.5
+offset_left = -144.0
+offset_top = -108.0
+offset_right = 144.0
+offset_bottom = 108.0
+grow_horizontal = 2
+grow_vertical = 2
+pivot_offset = Vector2(144, 108)
+
+[node name="ViewportContainer" type="SubViewportContainer" parent="ViewportHolder"]
+layout_mode = 1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+pivot_offset = Vector2(144, 108)
+
+[node name="SubViewport" type="SubViewport" parent="ViewportHolder/ViewportContainer"]
+handle_input_locally = false
+canvas_item_default_texture_filter = 0
+size = Vector2i(288, 216)
+render_target_update_mode = 4

autoloads/test_filter.tscn

@@ -0,0 +1,14 @@
+[gd_scene load_steps=3 format=3 uid="uid://bbrh8j4w6pgj2"]
+
+[ext_resource type="Shader" path="res://assets/shaders/test_filter.gdshader" id="1_un711"]
+
+[sub_resource type="ShaderMaterial" id="ShaderMaterial_au4vs"]
+shader = ExtResource("1_un711")
+
+[node name="TestFilter" type="ColorRect" groups=["screen_overlay"]]
+material = SubResource("ShaderMaterial_au4vs")
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2

project.godot

@@ -15,12 +15,15 @@ run/main_scene="res://maps/level1.tscn"
 config/features=PackedStringArray("4.3", "GL Compatibility")
 config/icon="res://icon.svg"
 
+[autoload]
+
+SceneManager="*res://autoloads/scene_manager.tscn"
+TestFilter="*res://autoloads/test_filter.tscn"
+
 [display]
 
 window/size/viewport_width=288
 window/size/viewport_height=216
-window/stretch/mode="viewport"
-window/stretch/scale_mode="integer"
 
 [editor_plugins]
 
@@ -31,11 +34,16 @@ enabled=PackedStringArray("res://addons/godot_state_charts/plugin.cfg")
 folder_colors={
 "res://addons/": "gray",
 "res://assets/": "yellow",
+"res://autoloads/": "orange",
 "res://maps/": "blue",
 "res://objects/": "red",
 "res://scripts/": "teal"
 }
 
+[global_group]
+
+screen_overlay="Autoload that will be rendered over the game viewport at full resolution."
+
 [layer_names]
 
 2d_physics/layer_1="solid"