Cloudy Tunnel Tweet Shader

#version 150
uniform float time;
uniform vec2 resolution;
in vec4 v_texcoord;
out vec4 FragColor;
 
#define PI 3.14159265
#define FC gl_FragCoord
 
mat2 rotate2D(float r)
{
    return mat2(cos(r), sin(r), -sin(r), cos(r));
}
 
mat3 rotate3D(float angle, vec3 axis)
{
    vec3 a = normalize(axis);
    float s = sin(angle);
    float c = cos(angle);
    float r = 1.0 - c;
    return mat3(
        a.x * a.x * r + c,
        a.y * a.x * r + a.z * s,
        a.z * a.x * r - a.y * s,
        a.x * a.y * r - a.z * s,
        a.y * a.y * r + c,
        a.z * a.y * r + a.x * s,
        a.x * a.z * r + a.y * s,
        a.y * a.z * r - a.x * s,
        a.z * a.z * r + c
    );
}
 
void main()
{
  vec2 r = resolution;
  float t = time;
 
  vec4 fcolor = vec4(1.0);
  vec3 p = vec3(0.0);
  float i=0,e=0,s=0,g=0,k=.005;
  for(;i++<2e2;g+=max(k,e*.2))
  {
    vec3 v=vec3(sin(e=t+g*.3),cos(e),4), p=vec3((FC.xy-.5*r)/r.y*g,g)*rotate3D(t,v);
    p.z+=t*4.;
    e=.3-dot(p.xy,p.xy);
    for(s=2.;s<2e2;s*=1.6)
    {
      p.yz*=rotate2D(s);
      e+=abs(dot(sin(p*s+t*s*.2)/s,p-p+1.));
    }
    fcolor += fcolor.w*min(e,k)*k;
  }
  FragColor = fcolor;
}