#ifdef GL_ES
precision mediump float;
#endif

const float pi = 3.141592653589793238462643383279502884; // atan(1.0) * 4.0;
uniform vec2 resolution;
uniform sampler2D iChannel0;

varying vec2 fragCoord;

float normpdf(in float x, in float sigma) {
    return 0.39894 * exp(-0.5 * x * x / (sigma * sigma)) / sigma;
}

vec4 texture(sampler2D s, vec2 c) {
  return texture2D(s, c);
}

void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    vec4 c = texture(iChannel0, fragCoord.xy / resolution.xy);

    //declare stuff
    const int mSize = 7;
    const int kSize = (mSize - 1) / 2;
    float kernel[mSize];
    vec4 final_colour = vec4(0.0);

    //create the 1-D kernel
    float sigma = 7.0;
    float Z = 0.0;
    for (int j = 0; j <= kSize; ++j) {
        kernel[kSize + j] = kernel[kSize - j] = normpdf(float(j), sigma);
    }

    //get the normalization factor (as the gaussian has been clamped)
    for (int j = 0; j < mSize; ++j) {
        Z += kernel[j];
    }

    //read out the texels
    for (int i = -kSize; i <= kSize; ++i) {
        for (int j=-kSize; j <= kSize; ++j) {
            final_colour += kernel[kSize + j] * kernel[kSize + i] * texture(iChannel0, (fragCoord.xy + vec2(float(i), float(j))) / resolution.xy);
        }
    }

    fragColor = (final_colour / (Z * Z));
}

void main(void) {
    mainImage(gl_FragColor, fragCoord.xy);
}