#version 330

/*
   Faded Film / Eastmancolor (1970s-1980s) — picom shader
   Warm Eastmancolor dye degradation. Taxi Driver, The Godfather era.
   Cyan dye fades first, magenta persists longest, lifted maroon blacks.
*/

in vec2 texcoord;
uniform sampler2D tex;

const vec3 LUMA = vec3(0.2126, 0.7152, 0.0722);

float hash(vec2 p) {
    vec3 p3 = fract(vec3(p.xyx) * .1031);
    p3 += dot(p3, p3.yzx + 33.33);
    return fract((p3.x + p3.y) * p3.z);
}

float vignette(vec2 uv) {
    vec2 d = uv - 0.5;
    float dist = length(d);
    return 1.0 - smoothstep(0.4, 1.1, dist) * 0.15;
}

vec4 window_shader() {
    vec2 texsize = textureSize(tex, 0);
    vec4 pixColor = texture2D(tex, texcoord / texsize, 0);
    vec3 color = pixColor.rgb;

    // Fade amount — 0.6 is moderate, recognizable but not extreme
    float fade = 0.6;

    // Cyan dye loss — red channel lifts as cyan absorption weakens
    color.r += 0.08 * fade;
    color.g += 0.02 * fade;

    // Yellow dye loss — blue channel loses contrast
    color.b -= 0.04 * fade;

    // Magenta shift — magenta dye persists longest
    float magentaShift = fade * 0.12;
    color.r += magentaShift;
    color.b += magentaShift * 0.3;
    color.g -= magentaShift * 0.5;

    // Lifted blacks to dark maroon (shadow density loss)
    float blackLift = fade * 0.08;
    color = max(color, vec3(blackLift * 1.2, blackLift * 0.7, blackLift * 0.5));

    // Desaturation — dye fading means less color intensity
    float luma = dot(color, LUMA);
    float desatAmount = mix(1.0, 0.65, fade);
    color = mix(vec3(luma), color, desatAmount);

    // Reduced contrast — faded prints are lower contrast
    color = mix(vec3(0.5), color, mix(1.0, 0.85, fade));

    // Warm color temperature shift
    color.r += 0.03 * fade;
    color.b -= 0.05 * fade;

    // Medium grain
    vec2 screenPos = gl_FragCoord.xy;
    float grain = (hash(screenPos * 0.6) - 0.5) * 0.04;
    // Luminance-dependent grain
    float grainMask = 1.0 - abs(luma - 0.5) * 1.5;
    grainMask = clamp(grainMask, 0.3, 1.0);
    color += grain * grainMask;

    // Vignette
    vec2 normalizedCoord = texcoord / texsize;
    color *= vignette(normalizedCoord);

    return vec4(clamp(color, 0.0, 1.0), 1.0);
}