uniform sampler2D u_Tex0;
varying vec2 v_TexCoord;

// some const, tweak for best look
const float sampleDist = 1.0;
const float sampleStrength = 2.2;

void main(void)
{
  // 0.5,0.5 is the center of the screen
  // so substracting v_TexCoord from it will result in
  // a vector pointing to the middle of the screen
  vec2 dir = 0.5 - v_TexCoord;

  // calculate the distance to the center of the screen
  float dist = sqrt(dir.x * dir.x + dir.y * dir.y);

  // normalize the direction (reuse the distance)
  dir = dir / max(dist, 0.001);

  // this is the original colour of this fragment
  // using only this would result in a nonblurred version
  vec4 color = texture2D(u_Tex0, v_TexCoord);

  vec4 sum = color;

  // take 10 additional blur samples in the direction towards
  // the center of the screen
  sum += texture2D(u_Tex0, v_TexCoord - 0.08 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord - 0.05 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord - 0.03 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord - 0.02 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord - 0.01 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord + 0.01 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord + 0.02 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord + 0.03 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord + 0.05 * dir * sampleDist);
  sum += texture2D(u_Tex0, v_TexCoord + 0.08 * dir * sampleDist);

  // we have taken eleven samples
  sum *= 1.0 / 11.0;

  // weighten the blur effect with the distance to the
  // center of the screen ( further out is blurred more)
  float t = dist * sampleStrength;
  t = clamp(t, 0.0, 1.0); //0 &lt;= t &lt;= 1

  //Blend the original color with the averaged pixels
  gl_FragColor = mix(color, sum, t);
}
