diff --git a/scenes/main.tscn b/scenes/main.tscn
index 6792ecb..8384d64 100644
--- a/scenes/main.tscn
+++ b/scenes/main.tscn
@@ -1,13 +1,18 @@
-[gd_scene load_steps=10 format=3 uid="uid://bjah7k4bxo044"]
+[gd_scene load_steps=12 format=3 uid="uid://bjah7k4bxo044"]
 
 [ext_resource type="Script" path="res://src/Main.gd" id="1_2625y"]
 [ext_resource type="Script" path="res://src/ImageViewport.gd" id="2_hvo65"]
+[ext_resource type="Shader" path="res://src/shader/ivd_outline.gdshader" id="3_6xihe"]
 [ext_resource type="Script" path="res://src/ImageViewportDisplay.gd" id="3_n4itb"]
-[ext_resource type="Shader" path="res://src/ui_background.gdshader" id="4_ty3qx"]
+[ext_resource type="Shader" path="res://src/shader/ui_background.gdshader" id="4_ty3qx"]
 [ext_resource type="Script" path="res://src/UIAppVersion.gd" id="5_o1ggv"]
 [ext_resource type="Script" path="res://src/Editor.gd" id="7_g8bap"]
 [ext_resource type="Script" path="res://src/Camera.gd" id="8_mls06"]
 
+[sub_resource type="ShaderMaterial" id="ShaderMaterial_y2ea0"]
+shader = ExtResource("3_6xihe")
+shader_parameter/zoom_level = Vector2(1, 1)
+
 [sub_resource type="ViewportTexture" id="ViewportTexture_lct1c"]
 viewport_path = NodePath("ImageViewport")
 
@@ -30,6 +35,7 @@ unique_name_in_owner = true
 
 [node name="ImageViewportDisplay" type="Sprite2D" parent="."]
 unique_name_in_owner = true
+material = SubResource("ShaderMaterial_y2ea0")
 texture = SubResource("ViewportTexture_lct1c")
 script = ExtResource("3_n4itb")
 
diff --git a/src/Camera.gd b/src/Camera.gd
index 1bc16f4..d30e160 100644
--- a/src/Camera.gd
+++ b/src/Camera.gd
@@ -29,17 +29,21 @@ func fit_image():
 		zoom = Vector2(zoomf, zoomf)
 		global_position = Vector2(-((ui_container_size.x) / 2 / zoom.x), 0)
 
+func update_viewport_display():
+	image_viewport_display.update_zoom_texture_filter(zoom)
+	image_viewport_display.material.set_shader_parameter("zoom_level", zoom)
+
 func zoom_in():
 	var old_mouse_pos = get_global_mouse_position()
 	zoom *= 1.2
 	global_position += old_mouse_pos - get_global_mouse_position()
-	image_viewport_display.update_zoom_texture_filter(zoom)
+	update_viewport_display()
 
 func zoom_out():
 	var old_mouse_pos = get_global_mouse_position()
 	zoom *= 1/1.2
 	global_position += old_mouse_pos - get_global_mouse_position()
-	image_viewport_display.update_zoom_texture_filter(zoom)
+	update_viewport_display()
 
 func _on_fit_image_button_pressed():
 	fit_image()
diff --git a/src/Globals.gd b/src/Globals.gd
index 0351452..727757e 100644
--- a/src/Globals.gd
+++ b/src/Globals.gd
@@ -1,7 +1,7 @@
 extends Node
 
 var camera_freeze = false
-@onready var shader: Shader = load("res://src/shaders/empty.gdshader")
+@onready var shader: Shader = load("res://src/shader/template.gdshader")
 var target_viewport: SubViewport
 var cwd = "."
 var last_image_savepath = ""
diff --git a/src/ImageViewport.gd b/src/ImageViewport.gd
index 207d283..fc05b5c 100644
--- a/src/ImageViewport.gd
+++ b/src/ImageViewport.gd
@@ -2,6 +2,7 @@ extends SubViewport
 
 @onready var camera = %Camera
 @onready var image_sprite = %ImageSprite
+@onready var image_viewport_display = %ImageViewportDisplay
 
 var image_original_tex: ImageTexture
 var image_result: Image
@@ -36,7 +37,7 @@ func update():
 	# load images from //!load directive -> TEXTURE
 	var regex_match = load_regex.search(Globals.shader.code)
 	if regex_match == null: # Error!
-		print("Didn't find any load directives!")
+		printerr("Didn't find any load directives!")
 		return
 	var tex_path = get_absolute_path(regex_match.strings[1])
 	load_texture(tex_path) # load every time
@@ -66,6 +67,7 @@ func update():
 	image_result = get_texture().get_image()
 	image_sprite.material = null
 	image_sprite.texture = ImageTexture.create_from_image(image_result)
+	image_viewport_display.show()
 
 func get_result():
 	return image_result
diff --git a/src/ImageViewportDisplay.gd b/src/ImageViewportDisplay.gd
index 9edcf83..7a9c827 100644
--- a/src/ImageViewportDisplay.gd
+++ b/src/ImageViewportDisplay.gd
@@ -1,5 +1,8 @@
 extends Sprite2D
 
+func _ready() -> void:
+	hide()
+
 func update_zoom_texture_filter(zoom: Vector2):
 	if zoom.x >= 1.5:
 		texture_filter = TEXTURE_FILTER_NEAREST_WITH_MIPMAPS
diff --git a/src/shader/ivd_outline.gdshader b/src/shader/ivd_outline.gdshader
new file mode 100644
index 0000000..14ce6e0
--- /dev/null
+++ b/src/shader/ivd_outline.gdshader
@@ -0,0 +1,16 @@
+shader_type canvas_item;
+
+uniform vec2 zoom_level = vec2(1.0);
+const float thickness = 3.0;
+
+void fragment() {
+	vec2 t = thickness * TEXTURE_PIXEL_SIZE / zoom_level;
+	if (
+		UV.x < t.x ||
+		UV.y < t.y ||
+		UV.x > 1.0-t.x ||
+		UV.y > 1.0-t.y
+	) {
+		COLOR = mix(COLOR, vec4(1.0), 0.5);
+	}
+}
diff --git a/src/shaders/empty.gdshader b/src/shader/template.gdshader
similarity index 100%
rename from src/shaders/empty.gdshader
rename to src/shader/template.gdshader
diff --git a/src/ui_background.gdshader b/src/shader/ui_background.gdshader
similarity index 100%
rename from src/ui_background.gdshader
rename to src/shader/ui_background.gdshader