#ifdef GL_ES
precision mediump float;
#endif
uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;
#define PI 3.14159265359

const vec3 uAColor = vec3(.0,.5,.5);
const vec3 uBColor = vec3(.0,.5,.5);
const vec3 uCColor = vec3(0.,.5,.333);
const vec3 uDColor = vec3(.0,.5,.667);

//get colors from http://dev.thi.ng/gradients/
vec3 cosPalette(float t) { return uAColor + uBColor*cos(6.28318*(uCColor*t+uDColor)); }

//2d perlin noise fn via stegu/webgl-noise
vec4 mod289(vec4 x) { return x - floor(x * (1.0 / 289.0)) * 289.0; }

vec4 permute(vec4 x) { return mod289(((x*34.0)+10.0)*x);}

vec4 taylorInvSqrt(vec4 r){ return 1.79284291400159 - 0.85373472095314 * r; }

vec2 fade(vec2 t) { return t*t*t*(t*(t*6.0-15.0)+10.0); }

// Classic Perlin noise
float cnoise(vec2 P)
{
  vec4 Pi = floor(P.xyxy) + vec4(0.0, 0.0, 1.0, 1.0);
  vec4 Pf = fract(P.xyxy) - vec4(0.0, 0.0, 1.0, 1.0);
  Pi = mod289(Pi); // To avoid truncation effects in permutation
  vec4 ix = Pi.xzxz;
  vec4 iy = Pi.yyww;
  vec4 fx = Pf.xzxz;
  vec4 fy = Pf.yyww;

  vec4 i = permute(permute(ix) + iy);

  vec4 gx = fract(i * (1.0 / 41.0)) * 2.0 - 1.0 ;
  vec4 gy = abs(gx) - 0.5 ;
  vec4 tx = floor(gx + 0.5);
  gx = gx - tx;

  vec2 g00 = vec2(gx.x,gy.x);
  vec2 g10 = vec2(gx.y,gy.y);
  vec2 g01 = vec2(gx.z,gy.z);
  vec2 g11 = vec2(gx.w,gy.w);

  vec4 norm = taylorInvSqrt(vec4(dot(g00, g00), dot(g01, g01), dot(g10, g10), dot(g11, g11)));
  g00 *= norm.x;  
  g01 *= norm.y;  
  g10 *= norm.z;  
  g11 *= norm.w;  

  float n00 = dot(g00, vec2(fx.x, fy.x));
  float n10 = dot(g10, vec2(fx.y, fy.y));
  float n01 = dot(g01, vec2(fx.z, fy.z));
  float n11 = dot(g11, vec2(fx.w, fy.w));

  vec2 fade_xy = fade(Pf.xy);
  vec2 n_x = mix(vec2(n00, n01), vec2(n10, n11), fade_xy.x);
  float n_xy = mix(n_x.x, n_x.y, fade_xy.y);
  return 2.3 * n_xy;
}

// Classic Perlin noise, periodic variant
float pnoise(vec2 P, vec2 rep)
{
  vec4 Pi = floor(P.xyxy) + vec4(0.0, 0.0, 1.0, 1.0);
  vec4 Pf = fract(P.xyxy) - vec4(0.0, 0.0, 1.0, 1.0);
  Pi = mod(Pi, rep.xyxy); // To create noise with explicit period
  Pi = mod289(Pi);        // To avoid truncation effects in permutation
  vec4 ix = Pi.xzxz;
  vec4 iy = Pi.yyww;
  vec4 fx = Pf.xzxz;
  vec4 fy = Pf.yyww;

  vec4 i = permute(permute(ix) + iy);

  vec4 gx = fract(i * (1.0 / 41.0)) * 2.0 - 1.0 ;
  vec4 gy = abs(gx) - 0.5 ;
  vec4 tx = floor(gx + 0.5);
  gx = gx - tx;

  vec2 g00 = vec2(gx.x,gy.x);
  vec2 g10 = vec2(gx.y,gy.y);
  vec2 g01 = vec2(gx.z,gy.z);
  vec2 g11 = vec2(gx.w,gy.w);

  vec4 norm = taylorInvSqrt(vec4(dot(g00, g00), dot(g01, g01), dot(g10, g10), dot(g11, g11)));
  g00 *= norm.x;  
  g01 *= norm.y;  
  g10 *= norm.z;  
  g11 *= norm.w;  

  float n00 = dot(g00, vec2(fx.x, fy.x));
  float n10 = dot(g10, vec2(fx.y, fy.y));
  float n01 = dot(g01, vec2(fx.z, fy.z));
  float n11 = dot(g11, vec2(fx.w, fy.w));

  vec2 fade_xy = fade(Pf.xy);
  vec2 n_x = mix(vec2(n00, n01), vec2(n10, n11), fade_xy.x);
  float n_xy = mix(n_x.x, n_x.y, fade_xy.y);
  return 2.3 * n_xy;
}

float stroke(in float x_coor, float s, float width){
  float d = step(s,x_coor+width*.5)-step(s,x_coor-width*.5);
  return clamp(d, 0.,1.);
}

float circleSDF(vec2 st) { return length(st-.5)*2.; }

void main() {
  vec2 st = gl_FragCoord.xy/u_resolution;
  float s = u_time/2.;
  float color = sin(s)*cos(s)/s*st.x;
  float alpha = 1.0;
  vec2 off = vec2(.2);
  float md = sin(u_time);
  int it = 8;
  for (int i = 0; i<it; i++) {
    color += stroke(circleSDF(st+(off*vec2(sin(s/md),cos(s/md)))), .3,(.1*abs(sin(s/md))));
    md *=2.;
  }
  color *= abs(pnoise(st+(10000.*cos(s)),st*sin(s)));
   
  gl_FragColor = vec4(cosPalette(color), alpha);
}