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);
}