Gaussian Shader Test

//Toggle Effects
#define DO_VIGNETTE 1
#define DO_GAUSSIANBLUR 1

//Effect Configurations
#define GAUSSIAN_SAMPLES 6

const float double_pi = 6.283185307179586476925286766559;
const float sigma = float(GAUSSIAN_SAMPLES) / 2.0;
const vec2 image_res = vec2(3860, 2160);
vec2 ps = vec2(1.0) / iResolution.xy;
float ar = iResolution.x / iResolution.y;

//Functions
vec2 scaleUV(vec2, vec2);
vec3 crop(sampler2D, vec2);
float gaussian_function(float);
float gaussian_function(vec2);
float gaussian_get_accum();

//Effects
vec3 GaussianBlur(sampler2D, vec2, vec2);
vec3 GaussianBlur(sampler2D, vec2);
void Vignette(inout vec3, vec2);

//Main Function
void main() {
    vec2 uv = gl_FragCoord.xy * ps;
    vec3 col = GaussianBlur(iChannel0, uv);
    Vignette(col, uv);
    gl_FragColor = vec4(col, 1.0);
}

vec2 scaleUV(vec2 uv, vec2 scale) {
    return (uv - 0.5) * scale + 0.5;
}

vec3 crop(sampler2D sp, vec2 uv) {
    return vec3(0.0);
}

float gaussian_function(float x) {
    const float first_part = 1.0 / sqrt(double_pi * pow(sigma, 2.0));
    const float second_part_a = 1.0 / (2.0 * pow(sigma, 2.0));
    float second_part_b = pow(x, 2.0) * second_part_a;
    return first_part * exp(-second_part_a);
}

float gaussian_function(vec2 i) {
    const float first_part = 1.0 / (double_pi * pow(sigma, 2.0));
    const float second_part_a = 1.0 / (2.0 * pow(sigma, 2.0));
    float second_part_b = (pow(i.x, 2.0) + pow(i.y, 2.0)) * second_part_a;
    return first_part * exp(-second_part_b);
}

float gaussian_get_accum() {
    float accum = 0.0;
    for (int i = -GAUSSIAN_SAMPLES; i <= GAUSSIAN_SAMPLES; ++i)
        accum += gaussian_function(float(i));
    return 1.0 / accum;
}

vec3 GaussianBlur(sampler2D sp, vec2 uv, vec2 dir) {
    #if !DO_GAUSSIANBLUR
    return texture2D(sp, uv).rgb;
    #endif
    vec3 col = vec3(0.0);
    float gauss_weight = 0.0;
    float accum = 0.0;
    for (int i = -GAUSSIAN_SAMPLES; i <= GAUSSIAN_SAMPLES; ++i) {
        gauss_weight = gaussian_function(float(i));
        col += texture2D(sp, uv + ps * dir * vec2(i)).rgb * gauss_weight;
        accum += gauss_weight;
    }
    return col / accum;
}

vec3 GaussianBlur(sampler2D sp, vec2 uv) {
    #if !DO_GAUSSIANBLUR
    return texture2D(sp, uv).rgb;
    #endif
    vec3 col = vec3(0.0);
    float gauss_weight = 0.0;
    float accum = 0.0;
    for (int x = -GAUSSIAN_SAMPLES; x <= GAUSSIAN_SAMPLES; ++x) {
        for (int y = -GAUSSIAN_SAMPLES; y <= GAUSSIAN_SAMPLES; ++y) {
            gauss_weight = gaussian_function(vec2(x, y));
            col += texture2D(sp, uv + ps * vec2(x, y)).rgb * gauss_weight;
            accum += gauss_weight;
        }
    }
    return col / accum;
}

void Vignette(inout vec3 col, vec2 uv) {
    #if DO_VIGNETTE
    col *= 1.0 - distance(uv, vec2(0.5));
    #endif
}