init

assets/shader/painterly_post_process.gdshader

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+shader_type canvas_item;
+
+uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap, repeat_disable;
+
+// --- Kuwahara (painterly smoothing) ---
+uniform int kuwahara_radius : hint_range(1, 10) = 4;
+
+// --- Edge / line art ---
+uniform float edge_strength : hint_range(0.0, 4.0) = 1.2;
+uniform float edge_threshold : hint_range(0.0, 1.0) = 0.12;
+uniform vec3 edge_color : source_color = vec3(0.05, 0.04, 0.03);
+
+// --- Brush / canvas texture overlay ---
+uniform sampler2D brush_tex : filter_linear_mipmap, repeat_enable;
+uniform vec2 brush_scale = vec2(18.0, 18.0);
+uniform float brush_strength : hint_range(0.0, 1.0) = 0.35;
+
+// --- Final color tweaks ---
+uniform float saturation : hint_range(0.0, 2.0) = 1.1;
+
+float luminance(vec3 c) {
+	return dot(c, vec3(0.299, 0.587, 0.114));
+}
+
+// Classic 4-quadrant Kuwahara filter
+vec3 kuwahara(sampler2D tex, vec2 uv, vec2 px, int r) {
+	vec3 mean[4];
+	float variance[4];
+
+	vec2 signs[4];
+	signs[0] = vec2(-1.0, -1.0);
+	signs[1] = vec2(1.0, -1.0);
+	signs[2] = vec2(-1.0, 1.0);
+	signs[3] = vec2(1.0, 1.0);
+
+	for (int q = 0; q < 4; q++) {
+		vec3 sum = vec3(0.0);
+		vec3 sum_sq = vec3(0.0);
+		float count = 0.0;
+		for (int j = 0; j <= r; j++) {
+			for (int i = 0; i <= r; i++) {
+				vec2 offset = vec2(float(i), float(j)) * signs[q] * px;
+				vec3 c = texture(tex, uv + offset).rgb;
+				sum += c;
+				sum_sq += c * c;
+				count += 1.0;
+			}
+		}
+		vec3 m = sum / count;
+		vec3 v = sum_sq / count - m * m;
+		mean[q] = m;
+		variance[q] = v.r + v.g + v.b;
+	}
+
+	float min_var = variance[0];
+	vec3 result = mean[0];
+	for (int q = 1; q < 4; q++) {
+		if (variance[q] < min_var) {
+			min_var = variance[q];
+			result = mean[q];
+		}
+	}
+	return result;
+}
+
+// Sobel edge detection on luminance
+float sobel_edge(sampler2D tex, vec2 uv, vec2 px) {
+	float tl = luminance(texture(tex, uv + vec2(-px.x, -px.y)).rgb);
+	float t  = luminance(texture(tex, uv + vec2(0.0, -px.y)).rgb);
+	float tr = luminance(texture(tex, uv + vec2(px.x, -px.y)).rgb);
+	float l  = luminance(texture(tex, uv + vec2(-px.x, 0.0)).rgb);
+	float r  = luminance(texture(tex, uv + vec2(px.x, 0.0)).rgb);
+	float bl = luminance(texture(tex, uv + vec2(-px.x, px.y)).rgb);
+	float b  = luminance(texture(tex, uv + vec2(0.0, px.y)).rgb);
+	float br = luminance(texture(tex, uv + vec2(px.x, px.y)).rgb);
+
+	float gx = -tl - 2.0 * l - bl + tr + 2.0 * r + br;
+	float gy = -tl - 2.0 * t - tr + bl + 2.0 * b + br;
+	return sqrt(gx * gx + gy * gy);
+}
+
+void fragment() {
+	vec2 uv = SCREEN_UV;
+	vec2 px = SCREEN_PIXEL_SIZE;
+
+	// STEP 1: painterly color smoothing
+	vec3 painted = kuwahara(SCREEN_TEXTURE, uv, px, kuwahara_radius);
+
+	// STEP 2: line art from the smoothed image (cleaner lines than raw noise)
+	float edge = sobel_edge(SCREEN_TEXTURE, uv, px);
+	edge = smoothstep(edge_threshold, edge_threshold + 0.3, edge) * edge_strength;
+	vec3 with_edges = mix(painted, edge_color, clamp(edge, 0.0, 1.0));
+
+	// STEP 3: brush / canvas texture overlay (fake stroke + paper grain)
+	vec3 brush = texture(brush_tex, uv * brush_scale).rgb;
+	vec3 with_brush = with_edges * mix(vec3(1.0), brush, brush_strength);
+
+	// STEP 4: slight saturation boost, like paint pigment richness
+	float l = luminance(with_brush);
+	vec3 final_color = mix(vec3(l), with_brush, saturation);
+
+	COLOR = vec4(final_color, 1.0);
+}