SF/05 · Seed 8

Night Mineral

A Julia boundary catches light like a fractured specimen.

The constant c travels a ring that hugs the Mandelbrot boundary, so every position is a different specimen. Escape time, a smooth iteration estimate and an orbit trap light rim and interior.

Palette · Midnight / copper / quartz
Interaction · Pointer walks c along the boundary · idle, it wanders by itself
Runtime · WebGL2 / fragment shader

Seed 8

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Time 6.00 s

Fragment shaderGLSL ES 3.00

#version 300 es
precision highp float;

uniform vec2 u_resolution;
uniform float u_time;
uniform vec2 u_pointer;   // 0–1, eased; drifts by itself while nobody is pointing
uniform vec3 u_click;     // xy = last press (0–1), z = seconds since that press
uniform float u_seed;
out vec4 outColor;

// Integer hash: a given seed renders the same work on every GPU.
uint hashu(uint x) {
    x ^= x >> 16; x *= 0x7feb352dU;
    x ^= x >> 15; x *= 0x846ca68bU;
    x ^= x >> 16;
    return x;
}

float seeded(uint k) {
    return float(hashu(uint(u_seed) * 0x9e3779b9U + k)) / 4294967295.0;
}

vec2 toField(vec2 q) {
    return (2.0 * q - 1.0) * u_resolution / min(u_resolution.x, u_resolution.y);
}

float dither(vec2 p) {
    return (fract(52.9829189 * fract(dot(p, vec2(0.06711056, 0.00583715)))) - 0.5) / 255.0;
}

void main() {
    vec2 uv = toField(gl_FragCoord.xy / u_resolution.xy);
    float turn = 0.06 * sin(u_time * 0.08);
    mat2 rotation = mat2(cos(turn), -sin(turn), sin(turn), cos(turn));

// c travels a ring that hugs the Mandelbrot boundary. The pointer moves it
    // along an arc chosen by the seed, so every position is a different specimen.
    float arc = 3.2 + (seeded(1u) - 0.5) * 1.2;
    float angle = arc + (u_pointer.x - 0.5) * 2.6 + 0.04 * sin(u_time * 0.1);
    float ring = 0.7885 + (seeded(2u) - 0.5) * 0.025 + (u_pointer.y - 0.5) * 0.02;
    vec2 c = ring * vec2(cos(angle), sin(angle));

vec2 z = rotation * uv * 1.35;
    float smoothIter = 0.0;
    float trap = 10.0;
    float escaped = 0.0;
    for (int i = 0; i < 160; i++) {
        z = vec2(z.x * z.x - z.y * z.y, 2.0 * z.x * z.y) + c;
        trap = min(trap, abs(z.y) + 0.4 * abs(z.x - 0.2));
        float m = dot(z, z);
        if (m > 256.0) {
            smoothIter = float(i) + 1.0 - log2(log2(m));
            escaped = 1.0;
            break;
        }
    }

int pick = int(floor(seeded(3u) * 3.0));
    vec3 midnight = vec3(0.012, 0.016, 0.05), copper = vec3(0.78, 0.29, 0.09), quartz = vec3(0.96, 0.86, 0.66);
    if (pick == 1) { midnight = vec3(0.02, 0.01, 0.05); copper = vec3(0.52, 0.22, 0.72); quartz = vec3(0.92, 0.86, 1.0); }
    if (pick == 2) { midnight = vec3(0.005, 0.03, 0.04); copper = vec3(0.10, 0.52, 0.56); quartz = vec3(0.86, 0.98, 0.94); }

float rim = smoothstep(2.0, 42.0, smoothIter);
    float facet = pow(0.5 + 0.5 * cos(smoothIter * 0.42), 5.0);
    vec3 color = mix(midnight, copper, rim) * escaped;
    color = mix(color, quartz, escaped * rim * rim * facet);
    vec3 interior = midnight * 1.6 + copper * 0.85 * exp(-24.0 * trap);
    color += (1.0 - escaped) * interior;
    outColor = vec4(color + dither(gl_FragCoord.xy), 1.0);
}

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The source above is the complete fragment shader. Changes remain in this tab unless you take them to the playground. Download the original GLSL.