precision highp float;

#define MEAN_SAMPLE  8

varying vec2 v_TexCoords;

uniform sampler2D u_Texture;
uniform float u_Alpha;
uniform float u_Value;
uniform vec2 u_RenderSize;

void main()
{
  const int kernelSize = 15;
  int smallKernelSize = ((kernelSize + 1) / MEAN_SAMPLE) + 1;
  float smallKernelSizeRcp = 1.0 / (float(smallKernelSize) * float(smallKernelSize));

  vec2 uv = vec2(v_TexCoords.x, 1.0 - v_TexCoords.y);
  vec2 duv = 1.0 / u_RenderSize;
  vec2 uv0 = uv - duv*0.5*float(smallKernelSize - 1);
  
  vec4 meanIp = vec4(0.0);
  vec4 corrIp = vec4(0.0);
  vec4 meanBA = vec4(0.0);

  for (int j = 0; j < smallKernelSize; j++) {
    for (int i = 0; i < smallKernelSize; i++) {
      vec2 texc = uv0 + duv * vec2(float(i), float(j));
      vec4 tex = texture2D(u_Texture, texc);
      meanBA += tex;
    }
  }
  meanBA *= smallKernelSizeRcp;

  gl_FragColor = meanBA;
}