void main() {
    float t_00 = rgb_2_luma(textureOffset(tex, uv, ivec2(-1,-1)).rgb);
    float t_01 = rgb_2_luma(textureOffset(tex, uv, ivec2(0,-1)).rgb);
    float t_02 = rgb_2_luma(textureOffset(tex, uv, ivec2(1,-1)).rgb);

    float t_10 = rgb_2_luma(textureOffset(tex, uv, ivec2(-1,0)).rgb);
    float t_11 = rgb_2_luma(textureOffset(tex, uv, ivec2(0,0)).rgb);
    float t_12 = rgb_2_luma(textureOffset(tex, uv, ivec2(1,0)).rgb);

    float t_20 = rgb_2_luma(textureOffset(tex, uv, ivec2(-1,1)).rgb);
    float t_21 = rgb_2_luma(textureOffset(tex, uv, ivec2(0,1)).rgb);
    float t_22 = rgb_2_luma(textureOffset(tex, uv, ivec2(1,1)).rgb);

    float gxin = -1*t_00 -2*t_01 -1*t_02 + 0*t_10 + 0*t_11 + 0*t_12 + 1*t_20 + 2*t_21 + 1*t_22;
    float gyin = -1*t_00 + 0*t_01 + 1*t_02 -2*t_10 + 0*t_11 + 2*t_12 -1*t_20 + 0*t_21 + 1*t_22;



    color = vec3(1.0 - sqrt(gxin*gxin + gyin*gyin));//texture(tex,uv).rgb;
}