#version 300 es
precision highp float;
uniform vec3 iResolution;
uniform float iTime;

out vec4 FragColor;

#define T (iTime)

float orb(vec3 p) {
    // orb time
    float t = T * 4.f;
    return length(p - vec3(sin(sin(t * .2f) + t * .4f) * 6.f, 1.f + sin(sin(t * .5f) + t * .2f) * 4.f, 12.f + T + cos(t * .3f) * 8.f));
}

void mainImage(out vec4 o, vec2 u) {
    float d, a, e, i, s, t = T;
    vec3 p = iResolution;    

    // scale coords
    u = (u + u - p.xy) / p.y;

    // camera movement
    u += vec2(cos(t * .1f) * .3f, cos(t * .3f) * .1f);

    for(o *= i; i++ < 128.f;

        // accumulate distance
        d += s = min(.03f + .2f * abs(s), e = max(.5f * e, .01f)),

        // grayscale color and orb light
        o += 1.f / (s + e * 3.f))

        // noise loop start, march
        for(p = vec3(u * d, d + t), // p = ro + rd *d, p.z + t;

            // entity (orb)
            e = orb(p) - .1f,

            // spin by t, twist by p.z
            p.xy *= mat2(cos(.1f * t + p.z / 8.f + vec4(0, 33, 11, 0))),

            // mirrored planes 4 units apart
            s = 4.f - abs(p.y),

            // noise starts at .8 up to 32., grow by a+=a
            a = .8f; a < 32.f; a += a)

            // apply turbulence
            p += cos(.7f * t + p.yzx) * .2f,

            // apply noise
            s -= abs(dot(sin(.1f * t + p * a), .6f + p - p)) / a;

    // tanh tonemap, brightness, light off-screen
    o = tanh(o / 1e1f);
}

void main() {
    mainImage(FragColor, gl_FragCoord.xy);
}