shader_type canvas_item;

uniform float sigma: hint_range(0.0, 20.0) = 3.3;

float gaussian(float x, float std) {
    return exp(x * x / (-2.0 * std * std)) / (sqrt(2.0 * PI) * std);
}

void fragment() {
    float ksize = round(3.0 * sigma);
    float std = (sigma != 0.0 ? sigma : 1.0);
    vec4 col = vec4(0.0);
    float total_weight = 0.0;
    for(float i = -ksize ; i <= ksize; ++i) {
        for(float j = -ksize; j <= ksize; ++j) {
            float weight = gaussian(i, std) * gaussian(j, std);
            col += texture(TEXTURE, UV + vec2(i, j) * SCREEN_PIXEL_SIZE) * weight;
            total_weight += weight;
        }
    }
    COLOR = col / total_weight;
}