#ifdef GL_ES
precision highp float;
#endif

varying vec2 vTexCoord;

uniform sampler2D image;
uniform vec2 imageSize;

void main() {
    vec2 texel = vec2(1.0 / imageSize.x, 1.0 / imageSize.y);
    vec4 color = vec4(0.0);
    color += texture2D(image, vTexCoord + vec2(texel.x * -1.0, texel.y * -1.0));
    color += texture2D(image, vTexCoord + vec2(texel.x *  0.0, texel.y * -1.0));
    color += texture2D(image, vTexCoord + vec2(texel.x * -1.0, texel.y *  0.0));
    color += texture2D(image, vTexCoord + vec2(texel.x *  0.0, texel.y *  0.0));
    gl_FragColor = color / 4.0;
}