float hash(vec2 p)
{
    return fract(
        sin(dot(p, vec2(127.1,311.7)))
        * 43758.5453123
    );
}

float noise(vec2 p)
{
    vec2 i = floor(p);
    vec2 f = fract(p);

    vec2 u =
        f*f*(3.0-2.0*f);

    return mix(
        mix(hash(i),
            hash(i+vec2(1,0)),u.x),
        mix(hash(i+vec2(0,1)),
            hash(i+vec2(1,1)),u.x),
        u.y
    );
}

float fbm(vec2 p)
{
    float v = 0.0;
    float a = 0.5;

    for(int i=0;i<5;i++)
    {
        v += a*noise(p);
        p *= 2.0;
        a *= 0.5;
    }

    return v;
}

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

    vec2 mouse =
        (2.0*iMouse.xy-iResolution.xy)
        / iResolution.y;

    if(iMouse.z<=0.0)
    {
        mouse =
            vec2(
                sin(iTime*0.15),
                cos(iTime*0.12)
            )*0.5;
    }

    float d =
        length(uv-mouse);

    float dent =
        exp(-d*6.0);

    float ripple =
        sin(
            d*30.0
            - iTime*4.0
        );

    ripple *= dent;

    vec2 flow =
        uv
        + normalize(
            uv-mouse
        )*ripple*0.03;

    float n =
        fbm(flow*4.0);

    float stars =
        smoothstep(
            0.82,
            1.0,
            n
        );

    vec3 col =
        vec3(
            0.02,
            0.05,
            0.12
        );

    col +=
        vec3(
            0.1,
            0.4,
            1.0
        )*dent*0.7;

    col +=
        vec3(
            0.3,
            0.7,
            1.0
        )*abs(ripple)*0.2;

    col +=
        vec3(1.0)
        * stars;

    float vignette =
        smoothstep(
            1.4,
            0.1,
            length(uv)
        );

    col *= vignette;

    fragColor =
        vec4(col,1.0);
}