#version 330

/*
   Kodachrome (1960s-1970s) — picom shader
   Warm, punchy reversal slide film.
   Vivid reds/yellows, suppressed greens, deep blacks, short highlight shoulder.
*/

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);
}

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

    // Kodachrome color matrix
    // Red boosted +15%, green suppressed -7%, blue +8%
    mat3 kodakMatrix = mat3(
        1.15,  0.05, -0.05,
       -0.05,  0.93,  0.02,
       -0.02, -0.05,  1.08
    );
    color = kodakMatrix * color;

    // Warm white balance offset
    color.r += 0.02;
    color.b -= 0.03;

    // Contrasty reversal-stock curve
    color = pow(max(color, vec3(0.0)), vec3(1.15));
    color = smoothstep(vec3(0.0), vec3(1.02), color);

    // Green suppression in midtones
    float luma = dot(color, LUMA);
    color.g = mix(color.g, color.g * 0.92, smoothstep(0.2, 0.6, luma));

    // Overall saturation boost 1.3x
    luma = dot(color, LUMA);
    color = mix(vec3(luma), color, 1.3);

    // Very fine grain — Kodachrome was nearly grainless
    vec2 screenPos = gl_FragCoord.xy;
    float grain = (hash(screenPos * 0.9) - 0.5) * 0.01;
    color += grain;

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