Gunkable props blend the underlying normal map where possible

assets/props/overhead_light/overhead_light_burnout_E.png.import

@@ -3,25 +3,27 @@
 importer="texture"
 type="CompressedTexture2D"
 uid="uid://b0vorb12h2idg"
-path="res://.godot/imported/overhead_light_burnout_E.png-ce71c7290fb299e0f7b60d0a9c7d4505.ctex"
+path.s3tc="res://.godot/imported/overhead_light_burnout_E.png-ce71c7290fb299e0f7b60d0a9c7d4505.s3tc.ctex"
+path.etc2="res://.godot/imported/overhead_light_burnout_E.png-ce71c7290fb299e0f7b60d0a9c7d4505.etc2.ctex"
 metadata={
-"vram_texture": false
+"imported_formats": ["s3tc_bptc", "etc2_astc"],
+"vram_texture": true
 }
 
 [deps]
 
 source_file="res://assets/props/overhead_light/overhead_light_burnout_E.png"
-dest_files=["res://.godot/imported/overhead_light_burnout_E.png-ce71c7290fb299e0f7b60d0a9c7d4505.ctex"]
+dest_files=["res://.godot/imported/overhead_light_burnout_E.png-ce71c7290fb299e0f7b60d0a9c7d4505.s3tc.ctex", "res://.godot/imported/overhead_light_burnout_E.png-ce71c7290fb299e0f7b60d0a9c7d4505.etc2.ctex"]
 
 [params]
 
-compress/mode=0
+compress/mode=2
 compress/high_quality=false
 compress/lossy_quality=0.7
 compress/hdr_compression=1
 compress/normal_map=0
 compress/channel_pack=0
-mipmaps/generate=false
+mipmaps/generate=true
 mipmaps/limit=-1
 roughness/mode=0
 roughness/src_normal=""
@@ -31,4 +33,4 @@ process/normal_map_invert_y=false
 process/hdr_as_srgb=false
 process/hdr_clamp_exposure=false
 process/size_limit=0
-detect_3d/compress_to=1
+detect_3d/compress_to=0

levels/sandbox/editor_visual_demo.tscn

@@ -91,6 +91,8 @@ shader_parameter/iridescence_intensity = 0.1
 shader_parameter/overlay_emission_scale = 1.0
 shader_parameter/edge_bleed = 0.25
 shader_parameter/gunk_mask = ExtResource("3_3t4ks")
+shader_parameter/base_uv_scale = Vector3(1, 1, 1)
+shader_parameter/normal_blend = 1.0
 
 [sub_resource type="ConcavePolygonShape3D" id="ConcavePolygonShape3D_gpcv6"]
 data = PackedVector3Array(4.5, 0, 4.5, -4.5, 0, 4.5, 4.5, 0, -4.5, 4.5, 0, -4.5, -4.5, 0, 4.5, -4.5, 0, -4.5)
@@ -243,6 +245,8 @@ shader_parameter/iridescence_intensity = 0.0
 shader_parameter/overlay_emission_scale = 1.0
 shader_parameter/edge_bleed = 0.25
 shader_parameter/gunk_mask = ExtResource("31_753oq")
+shader_parameter/base_uv_scale = Vector3(1, 1, 1)
+shader_parameter/normal_blend = 1.0
 
 [sub_resource type="StandardMaterial3D" id="StandardMaterial3D_k52xx"]
 resource_local_to_scene = true

src/shaders/gunk/common.gdshaderinc

@@ -72,6 +72,26 @@ float hardstep(float value) {
 	return 0.5 * tanh( (20.0 * x - 10.0) * inversesqrt(x - x * x) ) + 0.5;
 }
 
+vec3 slerp(vec3 a, vec3  b, float t) {
+    vec3 v0 = normalize(a);
+    vec3 v1 = normalize(b);
+
+    float cos_theta = clamp(dot(v0, v1), -1.0, 1.0);
+
+    // use lerp for small angles to avoid division by small sine
+    const float epsilon = 1e-6;
+    if (1.0 - abs(cos_theta) < epsilon) {
+        return normalize(mix(v0, v1, t));
+    }
+
+    float theta = acos(cos_theta);
+    float sin_theta = sin(theta);
+    float w0 = sin((1.0 - t) * theta) / sin_theta;
+    float w1 = sin(t * theta) / sin_theta;
+
+    return w0 * v0 + w1 * v1;
+}
+
 vec3 swirl_uvt(vec3 uvt) {
 	uvt.x += sin(uvt.y * 1.54 * PI + uvt.z) * cos(uvt.y * 1.31 * PI + uvt.z) * 0.2;
 	uvt.y += cos(uvt.x * 1.74 * PI + uvt.z) * -sin(uvt.y * 1.64 * PI + uvt.z) * 0.2;

src/shaders/gunk/gunk_overlay.gdshader

@@ -5,6 +5,11 @@ render_mode depth_prepass_alpha;
 #define USE_MASK
 #include "common.gdshaderinc"
 
+group_uniforms base_material;
+uniform vec3 base_uv_scale = vec3(1.0);
+uniform sampler2D base_normal_map: filter_linear;
+uniform float normal_blend = 1.0;
+
 void fragment() {
 	vec3 uvt = scale_uvt(UV, TIME);
 	float value = sample_noise(uvt);
@@ -13,16 +18,27 @@ void fragment() {
 	EMISSION = base_emission(UV, value);
 	SPECULAR = base_specular();
 
-	// vec3 nmap = minimal_convolution(UV, uvt);
-	// vec3 nmap = cross_convolution(UV, uvt);
-	vec3 nmap = sobel_convolution(UV, uvt);
-	// vec3 nmap = sobel_5x5_convolution(UV, uvt);
-    // vec3 nmap = scharr_convolution(UV, uvt);
-    // vec3 nmap = godot_convolution(UV, uvt);
-	NORMAL_MAP = nmap / 2.0 + 0.5;
+    mat3 TBN = mat3(TANGENT, BINORMAL, NORMAL);
+    mat3 inv_TBN = transpose(TBN);
+
+    vec3 base_nmap = texture(base_normal_map, UV * base_uv_scale.xy).rgb * 2.0 - 1.0;
+    vec3 base_world_normal = TBN * base_nmap;
+	vec3 gunk_nmap = sobel_convolution(UV, uvt);
+    vec3 gunk_world_normal = TBN * gunk_nmap;
+
+    // Unity blending
+    // see https://blog.selfshadow.com/publications/blending-in-detail/
+    vec3 n = base_nmap;
+    mat3 basis = mat3(
+        vec3(n.z, n.y, -n.x),
+        vec3(n.x, n.z, -n.y),
+        vec3(n.x, n.y, n.z)
+        );
+    vec3 nmap = normalize(gunk_nmap.x * basis[0] + gunk_nmap.y * basis[1] + gunk_nmap.z * basis[2]);
+    vec3 world_normal = TBN * nmap;
+    NORMAL_MAP = nmap / 2.0 + 0.5;
 
 	// add fresnel
-	vec3 world_normal = mat3(TANGENT, BINORMAL, NORMAL) * nmap;
 	EMISSION += rim_glow(
 		world_normal,
 		VIEW,

src/world/gunkable/gunkable.gd

@@ -22,6 +22,12 @@ const MASK_THRESHOLD := 0.5
 
 @export var source_gunk_material: ShaderMaterial
 
+@export_group("Base Materials")
+@export var base_material_index := 0
+@export var base_uv_scale := Vector3.ONE
+@export var base_normal_map: Texture2D
+@export var base_normal_blend := 0.6
+
 var meshtool := MeshDataTool.new()
 
 var _polyline_buffer: Array[Vector2] = []
@@ -68,6 +74,22 @@ func _ready() -> void:
 		mat_instance.next_pass = mesh_instance.material_overlay
 	mesh_instance.material_overlay = mat_instance
 
+	# Extract what we can from a base material, if we can find one.
+	var base_material: Material = mesh_instance.get_surface_override_material(base_material_index)
+	if not base_material:
+		base_material = mesh_instance.mesh.surface_get_material(base_material_index)
+	var standard_base_mat: StandardMaterial3D = base_material as StandardMaterial3D
+
+	if not base_normal_map and standard_base_mat:
+		base_normal_map = standard_base_mat.normal_texture
+		base_uv_scale = standard_base_mat.uv1_scale
+
+	if base_normal_map:
+		mat_instance.set_shader_parameter("base_normal_map", base_normal_map)
+		mat_instance.set_shader_parameter("normal_blend", base_normal_blend)
+
+	mat_instance.set_shader_parameter("base_uv_scale", base_uv_scale)
+
 	_deferred_init.call_deferred()
 
 	# Initialize meshtool