#version 300 es
precision highp float;

in vec2 v_texcoord;
uniform sampler2D tex;
out vec4 fragColor;

float blur_channel_r(vec2 center) {
    float o = 0.003;
    float c = 0.0;
    c += texture(tex, center + vec2(-o, -o)).r * 0.0625;
    c += texture(tex, center + vec2( 0, -o)).r * 0.125;
    c += texture(tex, center + vec2( o, -o)).r * 0.0625;
    c += texture(tex, center + vec2(-o,  0)).r * 0.125;
    c += texture(tex, center             ).r * 0.25;
    c += texture(tex, center + vec2( o,  0)).r * 0.125;
    c += texture(tex, center + vec2(-o,  o)).r * 0.0625;
    c += texture(tex, center + vec2( 0,  o)).r * 0.125;
    c += texture(tex, center + vec2( o,  o)).r * 0.0625;
    return c;
}

float blur_channel_g(vec2 center) {
    float o = 0.003;
    float c = 0.0;
    c += texture(tex, center + vec2(-o, -o)).g * 0.0625;
    c += texture(tex, center + vec2( 0, -o)).g * 0.125;
    c += texture(tex, center + vec2( o, -o)).g * 0.0625;
    c += texture(tex, center + vec2(-o,  0)).g * 0.125;
    c += texture(tex, center             ).g * 0.25;
    c += texture(tex, center + vec2( o,  0)).g * 0.125;
    c += texture(tex, center + vec2(-o,  o)).g * 0.0625;
    c += texture(tex, center + vec2( 0,  o)).g * 0.125;
    c += texture(tex, center + vec2( o,  o)).g * 0.0625;
    return c;
}

float blur_channel_b(vec2 center) {
    float o = 0.003;
    float c = 0.0;
    c += texture(tex, center + vec2(-o, -o)).b * 0.0625;
    c += texture(tex, center + vec2( 0, -o)).b * 0.125;
    c += texture(tex, center + vec2( o, -o)).b * 0.0625;
    c += texture(tex, center + vec2(-o,  0)).b * 0.125;
    c += texture(tex, center             ).b * 0.25;
    c += texture(tex, center + vec2( o,  0)).b * 0.125;
    c += texture(tex, center + vec2(-o,  o)).b * 0.0625;
    c += texture(tex, center + vec2( 0,  o)).b * 0.125;
    c += texture(tex, center + vec2( o,  o)).b * 0.0625;
    return c;
}

void main() {
    float chroma = 0.004;
    float a = texture(tex, v_texcoord).a;

    float r = blur_channel_r(v_texcoord + vec2( chroma, 0.0));
    float g = blur_channel_g(v_texcoord);
    float b = blur_channel_b(v_texcoord - vec2( chroma, 0.0));

    fragColor = vec4(r, g, b, a);
}