Using subviewport texture for gunk mask

levels/sandbox/sandbox.tscn

@@ -1,12 +1,11 @@
-[gd_scene load_steps=24 format=3 uid="uid://16ds4fvv72xk"]
+[gd_scene load_steps=23 format=3 uid="uid://16ds4fvv72xk"]
 
-[ext_resource type="Script" path="res://src/world/gunk_body.gd" id="1_csc4b"]
+[ext_resource type="PackedScene" uid="uid://c2omlx4ptrc01" path="res://src/world/gunk_body/gunk_body.tscn" id="1_a67lu"]
 [ext_resource type="PackedScene" uid="uid://bwe2jdmvinhqd" path="res://src/player/player.tscn" id="1_h436a"]
 [ext_resource type="ArrayMesh" uid="uid://lvats6ptrcxt" path="res://assets/props/icosahedron/icosahedron.obj" id="1_kvwui"]
 [ext_resource type="Shader" path="res://src/shaders/gunk.gdshader" id="2_utxkh"]
 [ext_resource type="Material" uid="uid://byyjoruj8mwe0" path="res://levels/sandbox/debug_gunk_mat.tres" id="3_o7v4k"]
 [ext_resource type="ArrayMesh" uid="uid://e6syamfwiitk" path="res://assets/props/monkey/monkey.obj" id="4_o55bf"]
-[ext_resource type="Script" path="res://levels/sandbox/debug_draw.gd" id="7_r3enw"]
 
 [sub_resource type="Environment" id="Environment_cc548"]
 background_mode = 1
@@ -114,9 +113,8 @@ mesh = SubResource("CylinderMesh_a1koa")
 [node name="CollisionShape3D" type="CollisionShape3D" parent="Geometry/Cylinder"]
 shape = SubResource("CylinderShape3D_uo57d")
 
-[node name="Icosahedron" type="StaticBody3D" parent="Geometry"]
+[node name="Icosahedron" parent="Geometry" instance=ExtResource("1_a67lu")]
 transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, -3.35498, 1.13294, -2.81423)
-script = ExtResource("1_csc4b")
 
 [node name="MeshInstance3D" type="MeshInstance3D" parent="Geometry/Icosahedron"]
 mesh = ExtResource("1_kvwui")
@@ -126,27 +124,15 @@ surface_material_override/0 = ExtResource("3_o7v4k")
 [node name="CollisionShape3D" type="CollisionShape3D" parent="Geometry/Icosahedron"]
 shape = SubResource("ConcavePolygonShape3D_nxc47")
 
-[node name="Monkey" type="StaticBody3D" parent="Geometry"]
+[node name="Monkey" parent="Geometry" instance=ExtResource("1_a67lu")]
 transform = Transform3D(-0.616239, 0, 0.787559, 0, 1, 0, -0.787559, 0, -0.616239, -2.22512, 1.41158, 2.88581)
-script = ExtResource("1_csc4b")
 
 [node name="MeshInstance3D" type="MeshInstance3D" parent="Geometry/Monkey"]
 mesh = ExtResource("4_o55bf")
+skeleton = NodePath("")
 surface_material_override/0 = SubResource("StandardMaterial3D_7cwtv")
 
 [node name="CollisionShape3D" type="CollisionShape3D" parent="Geometry/Monkey"]
 shape = SubResource("ConcavePolygonShape3D_hvf6a")
 
 [node name="Player" parent="." instance=ExtResource("1_h436a")]
-
-[node name="DebugDraw" type="Control" parent="."]
-unique_name_in_owner = true
-visible = false
-layout_mode = 3
-anchors_preset = 15
-anchor_right = 1.0
-anchor_bottom = 1.0
-grow_horizontal = 2
-grow_vertical = 2
-mouse_filter = 2
-script = ExtResource("7_r3enw")

src/player/player.gd

@@ -7,7 +7,7 @@ const JUMP_FORCE := 4.5
 const GROUND_FRICTION := 0.3
 const AIR_FRICTION := 0.03
 
-const SPRAY_RADIUS := 15
+const SPRAY_RADIUS := 8
 
 var gravity: Vector3 = (
 	ProjectSettings.get_setting("physics/3d/default_gravity")

src/shaders/gunk.gdshader

@@ -13,8 +13,6 @@ uniform highp sampler2D gunk_normal_map;
 
 
 void fragment() {
-	float mask = texture(gunk_mask, UV).r;
-	if(mask < 0.1) {
 	float value = texture(gunk_noise, UV).r;
 	vec4 color = mix(color_1, color_2, value);
 	float roughness_mix = value * roughness;
@@ -23,8 +21,5 @@ void fragment() {
 	ROUGHNESS = roughness_mix;
 	SPECULAR = 0.5 * inversesqrt(specular_contribution);
 	NORMAL_MAP = texture(gunk_normal_map, UV).xyz;
-		ALPHA = 1.0;
+	ALPHA = 1.0 - texture(gunk_mask, UV).r;
-	} else {
-		ALPHA = 0.0;
-	}
 }

src/world/gunk_body/draw_controller.gd

@@ -0,0 +1,22 @@
+class_name DrawController extends Control
+
+var _draw_queue: Array[Callable] = []
+
+var _dirty := true
+
+
+func queue_draw(op: Callable) -> void:
+	_draw_queue.push_back(op)
+	_dirty = true
+
+
+func _draw() -> void:
+	while _draw_queue:
+		var op: Callable = _draw_queue.pop_front()
+		op.call()
+
+
+func _process(_delta: float) -> void:
+	if _dirty:
+		queue_redraw()
+		_dirty = false

src/world/gunk_body/gunk_body.gd

@@ -1,34 +1,24 @@
 class_name GunkBody extends StaticBody3D
 ## StaticBody3D with an associated "gunkable" mesh.
 
-const MASK_DIM := 512
 const FACE_EPSILON := 0.4
 const MASK_COLOR := Color.RED
 
-@export var mask_image: Image
-
 var meshtool := MeshDataTool.new()
 
 @onready var mesh_instance: MeshInstance3D = $MeshInstance3D
 @onready var mesh: ArrayMesh = mesh_instance.mesh
 @onready var gunk_mat: ShaderMaterial = mesh_instance.get_surface_override_material(0).next_pass
 
-@onready var debug_draw: DebugDraw = %DebugDraw
+@onready var mask_viewport: SubViewport = %MaskViewport
+@onready var mask_control: DrawController = %MaskControl
 
 
 func _ready() -> void:
-	if not mask_image:
+	gunk_mat.set_shader_parameter("gunk_mask", mask_viewport.get_texture())
-		mask_image = Image.create_empty(MASK_DIM, MASK_DIM, false, Image.FORMAT_L8)
-		_update_gunk_material()
-
 	meshtool.create_from_surface(mesh, 0)
 
 
-## Must be called internally whenever `mask_image` is updated
-func _update_gunk_material() -> void:
-	gunk_mat.set_shader_parameter("gunk_mask", ImageTexture.create_from_image(mask_image))
-
-
 ## Transform cartesian coordinates to barycentric wrt the given triangle
 func _barycentric(p: Vector3, a: Vector3, b: Vector3, c: Vector3) -> Vector3:
 	var v0 := b - a
@@ -83,14 +73,10 @@ func _get_uv(point: Vector3, normal: Vector3) -> Vector2:
 
 ## Paint a rectangle on the mask at a given point & normal on the mesh.
 func paint_mask(point: Vector3, normal: Vector3, radius: int) -> void:
-	# debug_draw.draw_vector(normal, point)
 	var local_point := point * global_transform
 	var local_normal := normal * global_basis
 	var uv := _get_uv(local_point, local_normal)
 	if uv == Vector2.INF:
 		return
-	var px_center: Vector2i = Vector2i(uv * Vector2(mask_image.get_size()))
+	var px_center: Vector2 = uv * mask_control.size
-	var rect := Rect2i(px_center.x - radius, px_center.y - radius, 2 * radius, 2 * radius)
+	mask_control.queue_draw(func() -> void: mask_control.draw_circle(px_center, radius, MASK_COLOR))
-	mask_image.fill_rect(rect, MASK_COLOR)
-	# TODO: can we call this once after all painting in a single frame is finished?
-	_update_gunk_material()

src/world/gunk_body/gunk_body.tscn

@@ -0,0 +1,26 @@
+[gd_scene load_steps=3 format=3 uid="uid://c2omlx4ptrc01"]
+
+[ext_resource type="Script" path="res://src/world/gunk_body/gunk_body.gd" id="1_qqbpr"]
+[ext_resource type="Script" path="res://src/world/gunk_body/draw_controller.gd" id="2_kkcjw"]
+
+[node name="GunkBody" type="StaticBody3D"]
+script = ExtResource("1_qqbpr")
+
+[node name="MaskViewport" type="SubViewport" parent="."]
+unique_name_in_owner = true
+handle_input_locally = false
+msaa_2d = 3
+canvas_item_default_texture_filter = 0
+size = Vector2i(1024, 1024)
+render_target_clear_mode = 1
+render_target_update_mode = 4
+
+[node name="MaskControl" type="Control" parent="MaskViewport"]
+unique_name_in_owner = true
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+script = ExtResource("2_kkcjw")