ghostty glow effect

ghostty-glow.glsl

// A set of sample offsets (x, y) and corresponding weights
const vec3[24] samples = vec3[](
    vec3( 0.16937617,  0.98555148, 1.0),
    vec3(-1.33307083,  0.47214633, 0.70710678),
    vec3(-0.84643949, -1.51113871, 0.57735027),
    vec3( 1.55415568, -1.25880901, 0.5),
    vec3( 1.68136438,  1.47411459, 0.44721360),
    vec3(-1.27951577,  2.08874110, 0.40824829),
    vec3(-2.45758475, -0.97993734, 0.37796447),
    vec3( 0.58746414, -2.76674644, 0.35355339),
    vec3( 2.99771570,  0.11704940, 0.33333333),
    vec3( 0.41360842,  3.13511213, 0.31622777),
    vec3(-3.16714993,  0.98445990, 0.30151134),
    vec3(-1.57367138, -3.08602631, 0.28867513),
    vec3( 2.88820265, -2.15830616, 0.27735010),
    vec3( 2.71507790,  2.57455860, 0.26726124),
    vec3(-2.15040700,  3.22114106, 0.25819889),
    vec3(-3.65488588, -1.62536433, 0.25),
    vec3( 1.01307760, -3.99670787, 0.24253563),
    vec3( 4.22972367,  0.33081361, 0.23570226),
    vec3( 0.40107790,  4.34040741, 0.22941573),
    vec3(-4.31912457,  1.15981160, 0.22360680),
    vec3(-1.92090448, -4.16054395, 0.21821789),
    vec3( 3.86391223, -2.65898144, 0.21320072),
    vec3( 3.34862284,  3.43318002, 0.20851441),
    vec3(-2.87697336,  3.96522689, 0.20412415)
);

// Colors we want to detect
const vec3 targetColors[4] = vec3[](
    vec3(0.956, 0.933, 0.894), // #f4eee4
    vec3(0.212, 0.976, 0.965), // #36f9f6
    vec3(1.0,   1.0,   1.0  ), // #ffffff
    vec3(0.600, 0.271, 1.000)  // #9945ff
);

// Tint colors for bloom
const vec3 bloomColors[4] = vec3[](
    vec3(0.953, 0.624, 0.02),   // #f39f05
    vec3(0.533, 0.122, 0.988),  // #881ffc
    vec3(0.011, 0.933, 0.976),  // #03edf9
    vec3(0.533, 0.122, 0.988)   // #881ffc
);

// Per-color bloom strength
const float bloomStrength[4] = float[](
    0.20, // yellow-white
    0.15, // cyan
    0.10, // white
    0.15  // purple
);

// Distance threshold to treat two colors as a match
const float threshold = 0.1;

// Return index of the closest matching color if within threshold, otherwise -1
int getMatchingColorIndex(vec3 color) {
    int bestIndex = -1;
    float bestDist = 9999.0;
    for (int i = 0; i < 4; i++) {
        float d = distance(color, targetColors[i]);
        if (d < bestDist) {
            bestDist = d;
            bestIndex = i;
        }
    }
    return (bestDist < threshold) ? bestIndex : -1;
}

void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    vec2 uv = fragCoord.xy / iResolution.xy;
    vec4 color = texture(iChannel0, uv);

    // Step size for sampling around the pixel
    //vec2 step = vec2(1.414) / iResolution.xy;
    vec2 step = vec2(1.0) / iResolution.xy;

    // Accumulate bloom
    for (int i = 0; i < 24; i++) {
        vec3 s = samples[i];
        vec4 c = texture(iChannel0, uv + s.xy * step);

        // Check if this neighbor matches one of the target colors
        int idx = getMatchingColorIndex(c.rgb);
        if (idx != -1) {
            // Add bloom tint
            float w = s.z;
            color += vec4(bloomColors[idx], 0.0) * (bloomStrength[idx] * w);
        }
    }

    // Clamp final color
    fragColor = clamp(color, 0.0, 1.0);
}