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#include <octane-oslintrin.h>

#define MAX_ITERATIONS  10
#define MAX_KERNEL_SIZE 11 // MAX_ITERATIONS + 1

// OSL sample implementation of gaussian blur for Octane Render
shader GaussianBlur(
    color in = 0
        [[string label = "Input texture"]],
    int iterations = 5
        [[int min = 0, int max = MAX_ITERATIONS,
          string label = "Step count",
          string description = "Number of steps"]],
    float stepSize = 0.001
        [[float min = 0.00001, float max = 0.01,
          string label = "Step size",
          string description = "UV distance between steps"]],
    output color out = 0)
{
    if (iterations == 0)
    {
        // just return the input with the right UV mapping
        out =  _evaluateDelayed(in, u, v);
    }
    else
    {
        float kernel[MAX_KERNEL_SIZE];

        // initialize the kernel
        float normFactor = 0;
        for (int i = 0; i <= iterations; ++i)
        {
            // use normal probability density function with sigma = 7
            float n  = 0.05699175 * exp(-0.01020408 * i * i);
            normFactor += i == 0 ? n : 2*n;
            kernel[i] = n;
        }

        // average the neighbours
        color c  = 0;
        for (int i = -iterations; i <= iterations; ++i)
        {
            float n = kernel[iterations - abs(i)];
            for (int j = -iterations; j <= iterations; ++j)
            {
                float f = n * kernel[iterations - abs(j)];
                c += f * _evaluateDelayed(in, u + i * stepSize, v + j * stepSize);
            }
        }

        // calculate the final value
        out = c/(normFactor*normFactor);
    }
}