Volume Cloud

#include "math.h"

#pragma opname          v_volumecloud

#pragma oplabel         "Volume Cloud"

#pragma opicon          SHOP_surface

#pragma label   diff            "Diffuse"

#pragma label   clouddensity    "Cloud Density"

#pragma label   shadowdensity   "Shadow Density"

#pragma label   phase           "Scattering Phase"

#pragma label   receiveshadows  "Receive Shadows"

#pragma hint    diff            color

#pragma hint    Cd              hidden

#pragma hint    receiveshadows  toggle

#pragma range   clouddensity    0 10

#pragma range   shadowdensity   0 10

#pragma range   phase           -1 1

// Generated by Mantra

#pragma hint    density hidden

surface

volumecloud(float density = 1;

        vector diff=1;

        vector Cd = 1;

        float clouddensity = 1;

        float shadowdensity = 1;

        float phase = 0;

        int receiveshadows = 1)

{

    vector      clr;

    float       den = density;

    if (phase == 0)

        F = diff * Cd * isotropic();

    else

        F = diff * Cd * henyeygreenstein(phase);

    if (density > 0)

    {

        clr = 0;

        // Allow for different densities for shadowed and non-shadowed

        // surfaces.

        if (isshadowray())

            den *= shadowdensity;

        else

            den *= clouddensity;

        // Clamp the density

        den = max(den, 0);

        // Accumulate light from all directions.

        illuminance(P, {0, 1, 0}, PI, "density", 1.0)

        {

            if (receiveshadows)

                shadow(Cl);

            if (phase != 0)

                clr += Cl * eval_bsdf(F, normalize(-I), normalize(L));

            else

                clr += Cl * 0.5;

        }

        Of = (1 - exp(-den*dPdz));

        Cf = Of * Cd * diff;

        Cf *= clr;

    }

    else

    {

        Of = 0;

        Cf = 0;

    }

}