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#version 300 es
precision highp float;
in vec2 v_texcoord;
uniform sampler2D tex;
out vec4 fragColor;
// --- CONFIGURATION ---
const float edge_threshold = 0.15; // Sensitivity (0.05-0.5) - lower = more edges
const float edge_softness = 0.08; // Anti-aliasing amount
const float line_thickness = 1.0; // 1.0 = normal, 2.0 = thicker
const float line_darkness = 0.05; // 0.0 = pure black, higher = lighter
const float paper_brightness = 0.98; // Paper color
const float paper_grain = 0.03; // Paper texture intensity
const float noise_reduction = 0.5; // Reduces speckles in smooth areas
// ---------------------
float luminance(vec3 color) {
return dot(color, vec3(0.2126, 0.7152, 0.0722));
}
float hash12(vec2 p) {
vec3 p3 = fract(vec3(p.xyx) * 0.1031);
p3 += dot(p3, p3.yzx + 33.33);
return fract((p3.x + p3.y) * p3.z);
}
// Sample luminance with bounds checking
float sampleLum(vec2 uv) {
vec2 safe_uv = clamp(uv, 0.0, 1.0);
return luminance(texture(tex, safe_uv).rgb);
}
void main() {
vec2 screen_res = vec2(textureSize(tex, 0));
vec2 pixel_size = line_thickness / screen_res;
vec2 pixel_coords = v_texcoord * screen_res;
// Sobel kernel sampling with proper edge clamping
float tl = sampleLum(v_texcoord + vec2(-pixel_size.x, -pixel_size.y));
float t = sampleLum(v_texcoord + vec2( 0.0, -pixel_size.y));
float tr = sampleLum(v_texcoord + vec2( pixel_size.x, -pixel_size.y));
float l = sampleLum(v_texcoord + vec2(-pixel_size.x, 0.0));
float c = sampleLum(v_texcoord); // Center pixel
float r = sampleLum(v_texcoord + vec2( pixel_size.x, 0.0));
float bl = sampleLum(v_texcoord + vec2(-pixel_size.x, pixel_size.y));
float b = sampleLum(v_texcoord + vec2( 0.0, pixel_size.y));
float br = sampleLum(v_texcoord + vec2( pixel_size.x, pixel_size.y));
// Sobel operators
float Gx = (tr + 2.0 * r + br) - (tl + 2.0 * l + bl);
float Gy = (bl + 2.0 * b + br) - (tl + 2.0 * t + tr);
float gradient = sqrt(Gx * Gx + Gy * Gy);
// Calculate local variance for noise reduction
// (reduces speckles in smooth areas while preserving real edges)
float mean = (tl + t + tr + l + c + r + bl + b + br) / 9.0;
float variance = 0.0;
variance += (tl - mean) * (tl - mean);
variance += (t - mean) * (t - mean);
variance += (tr - mean) * (tr - mean);
variance += (l - mean) * (l - mean);
variance += (c - mean) * (c - mean);
variance += (r - mean) * (r - mean);
variance += (bl - mean) * (bl - mean);
variance += (b - mean) * (b - mean);
variance += (br - mean) * (br - mean);
variance = sqrt(variance / 9.0);
// Adaptive threshold: require stronger edges in noisy areas
float adaptive_threshold = edge_threshold + variance * noise_reduction;
// Smooth edge detection (anti-aliased)
float edge = smoothstep(
adaptive_threshold - edge_softness,
adaptive_threshold + edge_softness,
gradient
);
// Paper texture
float paper = paper_brightness;
paper -= hash12(pixel_coords * 0.4) * paper_grain;
paper -= hash12(pixel_coords * 2.1) * paper_grain * 0.4;
// Final blend
float final_value = mix(paper, line_darkness, edge);
fragColor = vec4(vec3(final_value), 1.0);
}
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