Add basic post processing shader

main.gd

@@ -3,7 +3,7 @@ class_name Main
 
 
 @onready var tree: SceneTree = get_tree()
-@onready var container: Control = $"PrimaryCanvas/SafeMarginContainer"
+@onready var ui_container: Control = $"InterfaceCanvas/SafeMarginContainer"
 
 
 ## The possible states the game can be in.
@@ -61,7 +61,7 @@ func build_menu() -> void:
 	scene_menu = SCENE_MENU.instantiate()
 	scene_menu.selected_play.connect(_on_menu_selected_play)
 	scene_menu.selected_options.connect(_on_menu_selected_options)
-	container.add_child(scene_menu)
+	ui_container.add_child(scene_menu)
 
 ## Destroy the [MainGame].
 func destroy_game() -> void:

main.tscn

@@ -1,15 +1,27 @@
-[gd_scene load_steps=3 format=3 uid="uid://b38wkla8e7rmo"]
+[gd_scene load_steps=4 format=3 uid="uid://b38wkla8e7rmo"]
 
 [ext_resource type="Script" path="res://main.gd" id="1_jyg3q"]
+[ext_resource type="Material" uid="uid://dpumcyplql08q" path="res://postprocess.material" id="2_3o1ux"]
 [ext_resource type="PackedScene" uid="uid://bkm7id1wdwywg" path="res://scenes/menu/safe_margin_container.tscn" id="2_ah6n8"]
 
 [node name="Main" type="Node"]
 script = ExtResource("1_jyg3q")
 starting_stage = 3
 
-[node name="PrimaryCanvas" type="CanvasLayer" parent="."]
+[node name="PostprocessingCanvas" type="CanvasLayer" parent="."]
 
-[node name="SafeMarginContainer" parent="PrimaryCanvas" instance=ExtResource("2_ah6n8")]
+[node name="ColorRect" type="ColorRect" parent="PostprocessingCanvas"]
+material = ExtResource("2_3o1ux")
+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="InterfaceCanvas" type="CanvasLayer" parent="."]
+
+[node name="SafeMarginContainer" parent="InterfaceCanvas" instance=ExtResource("2_ah6n8")]
 min_margin_left = 16
 min_margin_right = 16
 min_margin_top = 16

postprocess.gdshader

@@ -0,0 +1,10 @@
+shader_type canvas_item;
+
+uniform float intensity = 0.1;
+uniform sampler2D screen_texture : hint_screen_texture, repeat_disable, filter_nearest;
+
+void fragment() {
+	float color = round(fract(UV * 360.0).y);
+	vec4 tex = texture(screen_texture, SCREEN_UV);
+	COLOR = tex * (1.0 - intensity) + (tex * color * intensity);
+}