uniform sampler2D bgl_RenderedTexture;
uniform float bgl_RenderedTextureWidth;
uniform float bgl_RenderedTextureHeight;


float width = bgl_RenderedTextureWidth; //texture width
float height = bgl_RenderedTextureHeight; //texture height

vec2 inverse_buffer_size = vec2(1.0/width, 1.0/height);

float   lumRGB(vec3 v)
{   return dot(v, vec3(0.30, 0.59, 0.11));   }
 
void   main()
{
    vec2    UV = gl_TexCoord[0].st;
 
    float   w = 1.0; // filter width
 
    float   t = lumRGB(texture2D(bgl_RenderedTexture, UV + vec2(0.0, -1.0) * w * inverse_buffer_size).xyz),
          l = lumRGB(texture2D(bgl_RenderedTexture, UV + vec2(-1.0, 0.0) * w * inverse_buffer_size).xyz),
          r = lumRGB(texture2D(bgl_RenderedTexture, UV + vec2(1.0, 0.0) * w * inverse_buffer_size).xyz),
          b = lumRGB(texture2D(bgl_RenderedTexture, UV + vec2(0.0, 1.0) * w * inverse_buffer_size).xyz);
 
    vec2    n = vec2(-(t - b), r - l);
    float   nl = length(n);
 
    if   (nl < (1.0 / 16.0))
   gl_FragColor = texture2D(bgl_RenderedTexture, UV);
 
    else
    {
   n *= inverse_buffer_size / nl;
 
   vec4   o = texture2D(bgl_RenderedTexture, UV),
         t0 = texture2D(bgl_RenderedTexture, UV + n * 0.5) * 0.9,
         t1 = texture2D(bgl_RenderedTexture, UV - n * 0.5) * 0.9,
         t2 = texture2D(bgl_RenderedTexture, UV + n) * 0.75,
         t3 = texture2D(bgl_RenderedTexture, UV - n) * 0.75;
 
   gl_FragColor = (o + t0 + t1 + t2 + t3) / 4.3;
    }
}