bye bye 3D game objects

- remove 3D-based backgrounds, which use the terribly inefficient CSG objects
- add 2D hit line texture based on Reverse (@Yasu3D)

Scenes/Play.tscn

@@ -1,6 +1,6 @@
-[gd_scene load_steps=7 format=3 uid="uid://bqh00ot0csqmk"]
+[gd_scene load_steps=11 format=3 uid="uid://bqh00ot0csqmk"]
 
-[ext_resource type="PackedScene" uid="uid://bbvduvnoesla5" path="res://Things/TunnelObjects/3D/Background/Background.tscn" id="1_2wv7o"]
+[ext_resource type="Texture2D" uid="uid://dkohutwp0yujj" path="res://_Assets/Textures/BGLine.png" id="2_lkl1c"]
 
 [sub_resource type="Environment" id="Environment_nefjb"]
 ambient_light_source = 1
@@ -44,9 +44,25 @@ _surfaces = [{
 blend_shape_mode = 0
 shadow_mesh = SubResource("ArrayMesh_40gjx")
 
+[sub_resource type="ViewportTexture" id="ViewportTexture_ln6xl"]
+viewport_path = NodePath("2D Viewport")
+
 [sub_resource type="StandardMaterial3D" id="StandardMaterial3D_3rv8i"]
+resource_local_to_scene = true
 transparency = 1
 shading_mode = 0
+albedo_texture = SubResource("ViewportTexture_ln6xl")
+uv1_scale = Vector3(-1, 1, 1)
+
+[sub_resource type="Gradient" id="Gradient_djnn4"]
+colors = PackedColorArray(0, 0, 0, 1, 0, 0, 0, 0)
+
+[sub_resource type="GradientTexture1D" id="GradientTexture1D_vv2ac"]
+gradient = SubResource("Gradient_djnn4")
+width = 2048
+
+[sub_resource type="LabelSettings" id="LabelSettings_dj3ei"]
+font_size = 271
 
 [node name="Play" type="Node"]
 
@@ -57,22 +73,105 @@ environment = SubResource("Environment_nefjb")
 
 [node name="Camera3D" type="Camera3D" parent="Node3D"]
 transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1.095)
+current = true
 fov = 60.0
 near = 0.001
-far = 10.0
+far = 20.0
 
 [node name="Cone" type="Node3D" parent="Node3D"]
-visible = false
+transform = Transform3D(-4.37114e-08, 1, 0, -1, -4.37114e-08, 0, 0, 0, 1, 0, 0, 0)
 
 [node name="RootNode" type="Node3D" parent="Node3D/Cone"]
 
 [node name="Cylinder" type="MeshInstance3D" parent="Node3D/Cone/RootNode"]
-transform = Transform3D(100, 0, 0, 0, -1.19209e-05, 100, 0, -100, -1.19209e-05, 0, 0, 0)
+transform = Transform3D(100, 0, 0, 0, -4.37114e-06, 100, 0, -100, -4.37114e-06, 0, 0, 0)
 mesh = SubResource("ArrayMesh_qc82q")
 skeleton = NodePath("")
 surface_material_override/0 = SubResource("StandardMaterial3D_3rv8i")
 
-[node name="Background" parent="Node3D" instance=ExtResource("1_2wv7o")]
-transform = Transform3D(-1, 0, -8.74228e-08, 0, 1, 0, 8.74228e-08, 0, -1, 0, 0, 0)
+[node name="2D Viewport" type="SubViewport" parent="."]
+disable_3d = true
+own_world_3d = true
+transparent_bg = true
+handle_input_locally = false
+msaa_2d = 1
+size = Vector2i(1920, 1920)
+render_target_update_mode = 4
 
-[node name="Node2D" type="Node2D" parent="."]
+[node name="Base" type="Control" parent="2D Viewport"]
+clip_contents = true
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+
+[node name="Camera2D" type="Camera2D" parent="2D Viewport/Base"]
+position = Vector2(0, -1920)
+anchor_mode = 0
+enabled = false
+
+[node name="Shadow" type="TextureRect" parent="2D Viewport/Base"]
+layout_mode = 2
+offset_top = 1920.0
+offset_right = 100.0
+offset_bottom = 3840.0
+rotation = -1.5708
+texture = SubResource("GradientTexture1D_vv2ac")
+expand_mode = 1
+
+[node name="Line" type="TextureRect" parent="2D Viewport/Base"]
+layout_mode = 1
+anchors_preset = 7
+anchor_left = 0.5
+anchor_top = 1.0
+anchor_right = 0.5
+anchor_bottom = 1.0
+offset_left = -960.0
+offset_top = -25.0
+offset_bottom = -8.01501
+grow_horizontal = 2
+grow_vertical = 0
+texture = ExtResource("2_lkl1c")
+expand_mode = 1
+
+[node name="Line2" type="TextureRect" parent="2D Viewport/Base"]
+layout_mode = 1
+anchors_preset = 7
+anchor_left = 0.5
+anchor_top = 1.0
+anchor_right = 0.5
+anchor_bottom = 1.0
+offset_top = -25.0
+offset_right = 960.0
+offset_bottom = -8.01501
+grow_horizontal = 2
+grow_vertical = 0
+texture = ExtResource("2_lkl1c")
+expand_mode = 1
+
+[node name="Label" type="Label" parent="2D Viewport/Base"]
+layout_mode = 1
+anchors_preset = 2
+anchor_top = 1.0
+anchor_bottom = 1.0
+offset_top = -970.0
+offset_right = 1885.0
+offset_bottom = -4.99927
+grow_vertical = 0
+size_flags_vertical = 3
+text = "1 2 3 4 5 6 7 10"
+label_settings = SubResource("LabelSettings_dj3ei")
+horizontal_alignment = 1
+vertical_alignment = 2
+
+[node name="SubViewportContainer" type="SubViewportContainer" parent="."]
+anchors_preset = 2
+anchor_top = 1.0
+anchor_bottom = 1.0
+offset_top = -3000.0
+offset_right = 1920.0
+offset_bottom = -1080.0
+grow_vertical = 0
+stretch = true