FXAA algorithm

gistfile1.glsl

float FXAA_SPAN_MAX = 8.0;
float FXAA_REDUCE_MUL = 1.0/8.0;
float FXAA_REDUCE_MIN = 1.0/128.0;

vec3 rgbNW=texture2D(buf0,texCoords+(vec2(-1.0,-1.0)/frameBufSize)).xyz;
vec3 rgbNE=texture2D(buf0,texCoords+(vec2(1.0,-1.0)/frameBufSize)).xyz;
vec3 rgbSW=texture2D(buf0,texCoords+(vec2(-1.0,1.0)/frameBufSize)).xyz;
vec3 rgbSE=texture2D(buf0,texCoords+(vec2(1.0,1.0)/frameBufSize)).xyz;
vec3 rgbM=texture2D(buf0,texCoords).xyz;

vec3 luma=vec3(0.299, 0.587, 0.114);
float lumaNW = dot(rgbNW, luma);
float lumaNE = dot(rgbNE, luma);
float lumaSW = dot(rgbSW, luma);
float lumaSE = dot(rgbSE, luma);
float lumaM  = dot(rgbM,  luma);

float lumaMin = min(lumaM, min(min(lumaNW, lumaNE), min(lumaSW, lumaSE)));
float lumaMax = max(lumaM, max(max(lumaNW, lumaNE), max(lumaSW, lumaSE)));

vec2 dir;
dir.x = -((lumaNW + lumaNE) - (lumaSW + lumaSE));
dir.y =  ((lumaNW + lumaSW) - (lumaNE + lumaSE));

float dirReduce = max(
                      (lumaNW + lumaNE + lumaSW + lumaSE) * (0.25 * FXAA_REDUCE_MUL),
                      FXAA_REDUCE_MIN);

float rcpDirMin = 1.0/(min(abs(dir.x), abs(dir.y)) + dirReduce);

dir = min(vec2( FXAA_SPAN_MAX,  FXAA_SPAN_MAX),
          max(vec2(-FXAA_SPAN_MAX, -FXAA_SPAN_MAX),
              dir * rcpDirMin)) / frameBufSize;

vec3 rgbA = (1.0/2.0) * (
                         texture2D(buf0, texCoords.xy + dir * (1.0/3.0 - 0.5)).xyz +
                         texture2D(buf0, texCoords.xy + dir * (2.0/3.0 - 0.5)).xyz);
vec3 rgbB = rgbA * (1.0/2.0) + (1.0/4.0) * (
                                            texture2D(buf0, texCoords.xy + dir * (0.0/3.0 - 0.5)).xyz +
                                            texture2D(buf0, texCoords.xy + dir * (3.0/3.0 - 0.5)).xyz);
float lumaB = dot(rgbB, luma);

if((lumaB < lumaMin) || (lumaB > lumaMax)) {
    gl_FragColor.xyz=rgbA;
} else {
    gl_FragColor.xyz=rgbB;
}

I'm not an author of this. It was copied from somewhere. just search for FXAA on github, plenty examples.