text: // copy.frag
  
  #define SHADER_NAME SIMPLE_TEXTURE
  
  precision highp float;
  varying vec2 vTextureCoord;
  uniform float seed;
  uniform float noiseScale;
  
  vec4 permute(vec4 x) {  return mod(((x*34.0)+1.0)*x, 289.0);    }
  vec4 taylorInvSqrt(vec4 r) {    return 1.79284291400159 - 0.85373472095314 * r; }
  
  float snoise(vec3 v){
      const vec2  C = vec2(1.0/6.0, 1.0/3.0) ;
      const vec4  D = vec4(0.0, 0.5, 1.0, 2.0);
      
      vec3 i  = floor(v + dot(v, C.yyy) );
      vec3 x0 = v - i + dot(i, C.xxx) ;
      
      vec3 g = step(x0.yzx, x0.xyz);
      vec3 l = 1.0 - g;
      vec3 i1 = min( g.xyz, l.zxy );
      vec3 i2 = max( g.xyz, l.zxy );
      
      vec3 x1 = x0 - i1 + 1.0 * C.xxx;
      vec3 x2 = x0 - i2 + 2.0 * C.xxx;
      vec3 x3 = x0 - 1. + 3.0 * C.xxx;
      
      i = mod(i, 289.0 );
      vec4 p = permute( permute( permute( i.z + vec4(0.0, i1.z, i2.z, 1.0 )) + i.y + vec4(0.0, i1.y, i2.y, 1.0 )) + i.x + vec4(0.0, i1.x, i2.x, 1.0 ));
      
      float n_ = 1.0/7.0;
      vec3  ns = n_ * D.wyz - D.xzx;
      
      vec4 j = p - 49.0 * floor(p * ns.z *ns.z);
      
      vec4 x_ = floor(j * ns.z);
      vec4 y_ = floor(j - 7.0 * x_ );
      
      vec4 x = x_ *ns.x + ns.yyyy;
      vec4 y = y_ *ns.x + ns.yyyy;
      vec4 h = 1.0 - abs(x) - abs(y);
      
      vec4 b0 = vec4( x.xy, y.xy );
      vec4 b1 = vec4( x.zw, y.zw );
      
      vec4 s0 = floor(b0)*2.0 + 1.0;
      vec4 s1 = floor(b1)*2.0 + 1.0;
      vec4 sh = -step(h, vec4(0.0));
      
      vec4 a0 = b0.xzyw + s0.xzyw*sh.xxyy ;
      vec4 a1 = b1.xzyw + s1.xzyw*sh.zzww ;
      
      vec3 p0 = vec3(a0.xy,h.x);
      vec3 p1 = vec3(a0.zw,h.y);
      vec3 p2 = vec3(a1.xy,h.z);
      vec3 p3 = vec3(a1.zw,h.w);
      
      vec4 norm = taylorInvSqrt(vec4(dot(p0,p0), dot(p1,p1), dot(p2, p2), dot(p3,p3)));
      p0 *= norm.x;
      p1 *= norm.y;
      p2 *= norm.z;
      p3 *= norm.w;
      
      vec4 m = max(0.6 - vec4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.0);
      m = m * m;
      return 42.0 * dot( m*m, vec4( dot(p0,x0), dot(p1,x1), dot(p2,x2), dot(p3,x3) ) );
  }
  
  float snoise(float x, float y, float z){
      return snoise(vec3(x, y, z));
  }
  
  void main(void) {
  	const float scale = 1.0;
  
  	float noise = snoise(vTextureCoord.x * noiseScale, vTextureCoord.y * noiseScale, seed);
  	noise = abs(noise - 0.5);
  	float d = smoothstep(.4, .35, noise);
  
  
      gl_FragColor = vec4(vec3(0.0), d);
  }