#define PI 3.14159265359

mat2 rot(float a)
{
    float c = cos(a);
    float s = sin(a);
    return mat2(c,-s,s,c);
}

float machine(vec3 p)
{
    float t = iTime * 0.25;

    p.xy *= rot(t * 0.3);
    p.xz *= rot(t * 0.2);

    vec3 q = p;

    q = abs(q);
    q -= 1.0;

    float rings =
        abs(length(q.xy) - 1.0);

    float pipes =
        min(
            length(q.xy) - 0.15,
            min(
                length(q.yz) - 0.15,
                length(q.xz) - 0.15
            )
        );

    float core =
        length(p) - 0.5;

    return min(
        min(rings, pipes),
        core
    );
}

float map(vec3 p)
{
    float d = machine(p);

    vec3 r = mod(p, 4.0) - 2.0;

    d = min(d, machine(r));

    return d;
}

vec3 getNormal(vec3 p)
{
    vec2 e = vec2(0.001,0.0);

    return normalize(vec3(
        map(p+e.xyy)-map(p-e.xyy),
        map(p+e.yxy)-map(p-e.yxy),
        map(p+e.yyx)-map(p-e.yyx)
    ));
}

void mainImage(out vec4 fragColor, in vec2 fragCoord)
{
    vec2 uv =
        (2.0*fragCoord-iResolution.xy)
        / iResolution.y;

    vec3 ro = vec3(
        sin(iTime*0.15)*2.0,
        cos(iTime*0.10)*1.5,
        -6.0 + iTime*0.5
    );

    vec3 rd =
        normalize(vec3(uv,1.5));

    vec3 col = vec3(0.0);

    float t = 0.0;

    for(int i=0;i<120;i++)
    {
        vec3 p = ro + rd*t;

        float d = map(p);

        if(d<0.001)
        {
            vec3 n = getNormal(p);

            float glow =
                0.5 +
                0.5*sin(
                    p.z*0.5 +
                    iTime
                );

            col =
                vec3(
                    0.2,
                    0.6,
                    1.0
                ) * glow;

            col +=
                pow(
                    max(n.z,0.0),
                    8.0
                );

            break;
        }

        t += d * 0.7;

        if(t>40.0) break;
    }

    col += vec3(
        0.02,
        0.04,
        0.08
    );

    fragColor = vec4(col,1.0);
}