Sobel filter sampling for gunk normal maps

src/shaders/gunk/canvas_grunk.gdshader

@@ -1,3 +1,4 @@
+// -*- mode: glsl -*-
 /* Gunk shader adapted to a canvas item */
 shader_type canvas_item;
 

src/shaders/gunk/common.gdshaderinc

@@ -1,3 +1,4 @@
+// -*- mode: glsl -*-
 // Common logic for gunk shaders
 
 group_uniforms gunk_material;
@@ -36,6 +37,23 @@ uniform sampler2D overlay_albedo: hint_default_transparent, filter_nearest;
 uniform sampler2D overlay_emission: hint_default_transparent, filter_nearest;
 uniform float overlay_emission_scale = 1.0;
 
+#if defined(USE_MASK)
+group_uniforms gunk_mask;
+uniform float edge_bleed = 0.25;
+uniform sampler2D gunk_mask;
+#endif
+
+
+float bump_sample(vec2 uv, vec3 uvt, float dx, float dy) {
+	vec2 offset = vec2(dx / pixellation, dy / pixellation);
+	float height = texture(gunk_noise, uvt + vec3(offset, 0.0)).r;
+#if defined(USE_MASK)
+	float mask = texture(gunk_mask, uv + offset).r;
+    height *= smoothstep(1.0, 0.0, mask);
+#endif
+    return height;
+}
+
 vec3 rim_glow(
 	vec3 normal,
 	vec3 view,
@@ -89,3 +107,82 @@ vec3 base_emission(vec2 uv, float value) {
 float base_specular() {
 	return 0.5 * inversesqrt(specular_contribution);
 }
+
+// Convolution methods
+
+vec3 godot_convolution(vec2 uv, vec3 uvt) {
+    // from https://github.com/godotengine/godot/blob/master/core/io/image.cpp#L3758
+    float here = bump_sample(uv, uvt, 0.0, 0.0);
+    float to_right = bump_sample(uv, uvt, 1.0, 0.0);
+    float above = bump_sample(uv, uvt, 0.0, -1.0);
+    vec3 up = vec3(0.0, 1.0, (here - above) * bump_strength);
+    vec3 across = vec3(1.0, 0.0, (to_right - here) * bump_strength);
+    return normalize(cross(across, up));
+}
+
+vec3 minimal_convolution(vec2 uv, vec3 uvt) {
+	float h_center = bump_sample(uv, uvt, 0.0, 0.0);
+	float h_right = bump_sample(uv, uvt, 1.0, 0.0);
+	float h_down = bump_sample(uv, uvt, 0.0, 1.0);
+	float dX = (h_center - h_right);
+	float dY = (h_center - h_down);
+	float dZ = 1.0 / bump_strength;
+	return normalize(vec3(dX, dY, dZ));
+}
+
+vec3 cross_convolution(vec2 uv, vec3 uvt) {
+	float h_right = bump_sample(uv, uvt, 1.0, 0.0);
+	float h_down = bump_sample(uv, uvt, 0.0, 1.0);
+	float h_left = bump_sample(uv, uvt, -1.0, 0.0);
+	float h_up = bump_sample(uv, uvt, 0.0, -1.0);
+	float dX = (h_left - h_right);
+	float dY = (h_right - h_down);
+	float dZ = 1.0 / bump_strength * 2.0;
+	return normalize(vec3(dX, dY, dZ));
+}
+
+vec3 sobel_convolution(vec2 uv, vec3 uvt) {
+	float tl = bump_sample(uv, uvt, -1.0, -1.0);
+	float l = bump_sample(uv, uvt, -1.0, 0.0);
+	float bl = bump_sample(uv, uvt, -1.0, 1.0);
+	float t = bump_sample(uv, uvt, 0.0, -1.0);
+	float b = bump_sample(uv, uvt, 0.0, 1.0);
+	float tr = bump_sample(uv, uvt, 1.0, -1.0);
+	float r = bump_sample(uv, uvt, 1.0, 0.0);
+	float br = bump_sample(uv, uvt, 1.0, 1.0);
+	float dX = (tr + 2.0 * r + br) - (tl + 2.0 * l + bl);
+	float dY = (bl + 2.0 * b + br) - (tl + 2.0 * t + tr);
+	float dZ = 1.0 / bump_strength * 8.0;
+	return normalize(vec3(dX, dY, dZ));
+}
+
+vec3 scharr_convolution(vec2 uv, vec3 uvt) {
+	float tl = bump_sample(uv, uvt, -1.0, -1.0);
+	float l = bump_sample(uv, uvt, -1.0, 0.0);
+	float bl = bump_sample(uv, uvt, -1.0, 1.0);
+	float t = bump_sample(uv, uvt, 0.0, -1.0);
+	float b = bump_sample(uv, uvt, 0.0, 1.0);
+	float tr = bump_sample(uv, uvt, 1.0, -1.0);
+	float r = bump_sample(uv, uvt, 1.0, 0.0);
+	float br = bump_sample(uv, uvt, 1.0, 1.0);
+	float dX = 3.0*tl + 10.0*l + 3.0*bl - 3.0*tr - 10.0*r - 3.0*br;
+	float dY = 3.0*tl + 10.0*t + 3.0*tr - 3.0*bl - 10.0*b - 3.0*br;
+	float dZ = 1.0 / bump_strength * 12.0;
+	return normalize(vec3(dX, dY, dZ));
+}
+
+vec3 sobel_5x5_convolution(vec2 uv, vec3 uvt) {
+    // Expensive!!
+    // TODO this can be decomposed into a few small matrix ops
+    float s[25];
+    for (int i = 0; i < 5; i++) {
+        for (int j = 0; j < 5; j++) {
+            s[i*5 + j] = bump_sample(uv, uvt, float(i - 2), float(j - 2));
+        }
+    }
+
+    float dX = 4.0 * (s[3] + s[23] - s[1] - s[21]) + 5.0 * (s[4] + s[24] - s[0] - s[20]) + 8.0 * (s[9] + s[19] - s[5] - s[15]) + 10.0 * (s[8] + s[14] + s[18] - s[6] - s[10] - s[16]) + 20.0 * (s[13] - s[11]);
+    float dY = 4.0 * (s[19] + s[15] - s[9] - s[5]) + 5.0 * (s[24] + s[20] - s[4] - s[0]) + 8.0 * (s[23] + s[21] - s[3] - s[1]) + 10.0 * (s[18] + s[22] + s[16] - s[8] - s[2] - s[6]) + 20.0 * (s[17] - s[7]);
+    float dZ = 1.0 / bump_strength * 240.0;
+    return normalize(vec3(dX, dY, dZ));
+}

src/shaders/gunk/debug_overlay.gdshader

@@ -1,31 +1,16 @@
+// -*- mode: glsl -*-
 shader_type spatial;
 render_mode depth_prepass_alpha, unshaded;
 
+#define USE_MASK
 #include "common.gdshaderinc"
 
-group_uniforms gunk_mask;
-uniform float edge_bleed = 0.25;
-uniform sampler2D gunk_mask;
-
-
-float bump_sample(vec2 uv, vec3 uvt, float dx, float dy) {
-	vec2 offset = vec2(dx / pixellation, dy / pixellation);
-	float height = texture(gunk_noise, uvt + vec3(offset, 0.0)).r;
-	float mask = texture(gunk_mask, uv + offset / uv_scale).r;
-	return height * smoothstep(1.0, 0.0, mask);
-}
 
 void fragment() {
 	vec3 uvt = scale_uvt(UV, TIME);
 	float value = sample_noise(uvt);
 
 
-	// Build normal map from bump map
+    vec3 nmap = sobel_convolution(UV, uvt);
-	float h_center = bump_sample(UV, uvt, 0.0, 0.0);
+	ALBEDO = nmap / 2.0 + 0.5;
-	float h_right = bump_sample(UV, uvt, 1.0, 0.0);
-	float h_down = bump_sample(UV, uvt, 0.0, 1.0);
-	float dx = (h_center - h_right) * bump_strength;
-	float dy = (h_center - h_down) * bump_strength;
-	vec3 normal_diff_map = normalize(vec3(dx, dy, 1.0));
-	ALBEDO = normal_diff_map / 2.0 + 0.5;
 }

src/shaders/gunk/gunk.gdshader

@@ -1,3 +1,4 @@
+// -*- mode: glsl -*-
 shader_type spatial;
 render_mode depth_prepass_alpha;
 
@@ -23,11 +24,6 @@ void vertex() {
 	VERTEX *= 1.0 + jitter;
 }
 
-float bump_sample(vec3 uvt, float dx, float dy) {
-	vec2 offset = vec2(dx / pixellation, dy / pixellation);
-	return texture(gunk_noise, uvt + vec3(offset, 0.0)).r;
-}
-
 void fragment() {
 	vec3 uvt = scale_uvt(UV, TIME);
 	float value = sample_noise(uvt);
@@ -36,17 +32,11 @@ void fragment() {
 	EMISSION = base_emission(UV, value);
 	SPECULAR = base_specular();
 
-	// Build normal map from bump map
+    vec3 nmap = sobel_convolution(UV, uvt);
-	float h_center = bump_sample(uvt, 0.0, 0.0);
+	NORMAL_MAP = nmap / 2.0 + 0.5;
-	float h_right = bump_sample(uvt, 1.0, 0.0);
-	float h_down = bump_sample(uvt, 0.0, 1.0);
-	float dx = (h_center - h_right) * bump_strength;
-	float dy = (h_center - h_down) * bump_strength;
-	vec3 normal_diff_map = normalize(vec3(dx, dy, 1.0));
-	NORMAL_MAP = normal_diff_map / 2.0 + 0.5;
 
 	// add fresnel
-	vec3 world_normal = mat3(TANGENT, BINORMAL, NORMAL) * normal_diff_map;
+	vec3 world_normal = mat3(TANGENT, BINORMAL, NORMAL) * nmap;
 	EMISSION += rim_glow(
 		world_normal,
 		VIEW,

src/shaders/gunk/gunk_overlay.gdshader

@@ -1,20 +1,10 @@
+// -*- mode: glsl -*-
 shader_type spatial;
 render_mode depth_prepass_alpha;
 
+#define USE_MASK
 #include "common.gdshaderinc"
 
-group_uniforms gunk_mask;
-uniform float edge_bleed = 0.25;
-uniform sampler2D gunk_mask;
-
-
-float bump_sample(vec2 uv, vec3 uvt, float dx, float dy) {
-	vec2 offset = vec2(dx / pixellation, dy / pixellation);
-	float height = texture(gunk_noise, uvt + vec3(offset, 0.0)).r;
-	float mask = texture(gunk_mask, uv + offset / uv_scale).r;
-	return height * smoothstep(1.0, 0.0, mask);
-}
-
 void fragment() {
 	vec3 uvt = scale_uvt(UV, TIME);
 	float value = sample_noise(uvt);
@@ -23,17 +13,16 @@ void fragment() {
 	EMISSION = base_emission(UV, value);
 	SPECULAR = base_specular();
 
-	// Build normal map from bump map
+	// vec3 nmap = minimal_convolution(UV, uvt);
-	float h_center = bump_sample(UV, uvt, 0.0, 0.0);
+	// vec3 nmap = cross_convolution(UV, uvt);
-	float h_right = bump_sample(UV, uvt, 1.0, 0.0);
+	vec3 nmap = sobel_convolution(UV, uvt);
-	float h_down = bump_sample(UV, uvt, 0.0, 1.0);
+	// vec3 nmap = sobel_5x5_convolution(UV, uvt);
-	float dx = (h_center - h_right) * bump_strength;
+    // vec3 nmap = scharr_convolution(UV, uvt);
-	float dy = (h_center - h_down) * bump_strength;
+    // vec3 nmap = godot_convolution(UV, uvt);
-	vec3 normal_diff_map = normalize(vec3(dx, dy, 1.0));
+	NORMAL_MAP = nmap / 2.0 + 0.5;
-	NORMAL_MAP = normal_diff_map / 2.0 + 0.5;
 
 	// add fresnel
-	vec3 world_normal = mat3(TANGENT, BINORMAL, NORMAL) * normal_diff_map;
+	vec3 world_normal = mat3(TANGENT, BINORMAL, NORMAL) * nmap;
 	EMISSION += rim_glow(
 		world_normal,
 		VIEW,