precision highp float;

uniform sampler2D tInput;

varying highp vec2 j;

void main(void)
{
    float o=0.25/256.0;

    gl_FragColor = 0.25 * (
        texture2D(tInput,j+vec2(o,o))
        +texture2D(tInput,j+vec2(o,-o))
        +texture2D(tInput,j+vec2(-o,o))
        +texture2D(tInput,j+vec2(-o,-o))
    ); 
}