alligator/alligator.C

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/// Alligator Noise is provided by Side Effects Software Inc. and is licensed
/// under a Creative Commons Attribution-ShareAlike 4.0 International License.
///
/// {
///  "dct:Title"  : "Alligator Noise",
///  "dct:Source" : "http://www.sidefx.com/docs/hdk15.0/alligator_2alligator_8_c-example.html"
///  "license"    : "http://creativecommons.org/licenses/by-sa/4.0/",
///  "cc:attributionName" : "Side Effects Software Inc",
/// }
/// 

///
/// This code is intended to be reference implementation of Houdini's Alligator
/// Noise algorithm.  It is not an optimal implementation by any means.
///
/// @note When using the Houdini's HDK, it's much easier to simply call @code
/// #include <UT/UT_Noise.h>
/// static UT_Noise     alligatorNoise(0, UT_Noise::ALLIGATOR);
/// static double
/// alligator(const UT_Vector3 &pos)
/// {
///    return alligatorNoise.turbulence(pos, 0);
/// }
/// @endcode

#include <math.h>
#include <queue>
#include <hboost/functional/hash.hpp>
#include <stdlib.h>
#include <UT/UT_DSOVersion.h>
#include <UT/UT_Vector3.h>
#include <VEX/VEX_VexOp.h>

namespace HDK_Sample {

static double
frandom(std::size_t hash)
{
#if 1
    // For VEX, we need something that produces the same results in a
    // thread-safe fashion (thus random() and even random_r() are not
    // possibilities).
    uint        seed = hash & (0xffffffff);
    return SYSfastRandom(seed);
#else
    srandom(hash);
    return double(random()) * (1.0/RAND_MAX);
#endif
}

static double
hash(int ix, int iy, int iz)
{
    std::size_t hash = 0;
    hboost::hash_combine(hash, ix);
    hboost::hash_combine(hash, iy);
    hboost::hash_combine(hash, iz);
    return frandom(hash);
}

// These hash functions permute indices differently to make different values
static double hash_1(int ix, int iy, int iz) { return hash(ix, iy, iz); }
static double hash_2(int ix, int iy, int iz) { return hash(iy, iz, ix); }
static double hash_3(int ix, int iy, int iz) { return hash(iz, ix, iy); }
static double hash_4(int ix, int iy, int iz) { return hash(ix, iz, iy); }

static double
rbf(double d)
{
    // Radial basis function
    auto smooth = [](double d) { return d*d*(3 - 2*d); };
    return d < 1 ? smooth(1-d) : 0;
}

static void
getCenter(int ix, int iy, int iz, const int ipos[3], double center[3])
{
    // Compute the center point for the given noise cell
    // hash_* is a function which takes the seeds and returns a random double
    // between 0 and 1.
    center[0] = hash_1(ix+ipos[0], iy+ipos[1], iz+ipos[2]) + ix;
    center[1] = hash_2(ix+ipos[0], iy+ipos[1], iz+ipos[2]) + iy;
    center[2] = hash_3(ix+ipos[0], iy+ipos[1], iz+ipos[2]) + iz;
}

double
noiseValue(int ix, int iy, int iz, const int ipos[3])
{
    return hash_4(ix+ipos[0], iy+ipos[1], iz+ipos[2]);
}

static double
distance(const double *p0, const double *p1)
{
    // Distance from one point to another
    double      sum = 0;
    for (int i = 0; i < 3; ++i)
        sum += (p0[i]-p1[i]) * (p0[i]-p1[i]);
    return SYSsqrt(sum);
}

static double
alligator(const double pos[3])
{
    int                         ipos[3]; // Integer coordinates
    double                      fpos[3]; // Fractional coordinates
    double                      vpos[3]; // Sparse point
    int                         idx = 0;
    std::priority_queue<double> nvals;

    for (int i = 0; i < 3; ++i)
    {
        ipos[i] = floor(pos[i]);
        fpos[i] = pos[i] - ipos[i];
    }
    for (int ix = -1; ix <= 1; ++ix)
    {
        for (int iy = -1; iy <= 1; ++iy)
        {
            for (int iz = -1; iz <= 1; ++iz, ++idx)
            {
                getCenter(ix, iy, iz, ipos, vpos);
                double  d = distance(fpos, vpos);
                if (d < 1)
                {
                    // Scale value by noise associated with the point.
                    double      v = noiseValue(ix, iy, iz, ipos) * rbf(d);
                    nvals.push(v);
                }
            }
        }
    }
    if (!nvals.size())
        return 0;

    double max = nvals.top();
    nvals.pop();
    if (nvals.size())
        max -= nvals.top();
    return max;
}

/// VEX callback to implement: float alligator(vector pos);
static void
alligator_Evaluate(int, void *argv[], void *)
{
    auto result = (float *)argv[0];
    auto fpos = ((const UT_Vector3 *)argv[1])->data();
    double      pos[3];
    std::copy(fpos, fpos+3, pos);
    *result = alligator(pos);
}

}

using namespace HDK_Sample;

void
newVEXOp(void *)
{
    new VEX_VexOp("alligator@&FV",
                    alligator_Evaluate,
                    VEX_ALL_CONTEXT,
                    nullptr,
                    nullptr);
}