Separable Gaussian

static const int iBlurSamples = 21;

inline float GetGaussAccum() {
    int n = iBlurSamples;
    for (int i = 0; i < iBlurSamples; ++i) {
        n += i + i;
    }
    return 1.0 / float(n);
}

float3 Gauss(sampler sp, float2 uv, float2 dir) {
    float3 col = tex2D(sp, uv).rgb * float(iBlurSamples);
    static const float accum = GetGaussAccum();
    for (int i = 1; i < iBlurSamples; ++i) {
        float weight = float(iBlurSamples - i);
        col += tex2D(sp, uv + PixelSize * dir * float(i)).rgb * weight;
        col += tex2D(sp, uv - PixelSize * dir * float(i)).rgb * weight;
    }
    return col * accum;
}