/*
 * Copyright 2011-2013 Blender Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "stdcycles.h"

shader node_principled_volume(color Color = color(0.5, 0.5, 0.5),
                              float Density = 1.0,
                              float Anisotropy = 0.0,
                              color AbsorptionColor = color(0.0, 0.0, 0.0),
                              float EmissionStrength = 0.0,
                              color EmissionColor = color(1.0, 1.0, 1.0),
                              float BlackbodyIntensity = 0.0,
                              color BlackbodyTint = color(1.0, 1.0, 1.0),
                              float Temperature = 1500.0,
                              string DensityAttribute = "geom:density",
                              string ColorAttribute = "geom:color",
                              string TemperatureAttribute = "geom:temperature",
                              output closure color Volume = 0)
{
  /* Compute density. */
  float primitive_density = 1.0;
  float density = max(Density, 0.0);

  if (density > 1e-5) {
    if (getattribute(DensityAttribute, primitive_density)) {
      density = max(density * primitive_density, 0.0);
    }
  }

  if (density > 1e-5) {
    /* Compute scattering color. */
    color scatter_color = Color;
    color primitive_color;
    if (getattribute(ColorAttribute, primitive_color)) {
      scatter_color *= primitive_color;
    }

    /* Add scattering and absorption closures. */
    color scatter_coeff = scatter_color;
    color absorption_color = sqrt(max(AbsorptionColor, 0.0));
    color absorption_coeff = max(1.0 - scatter_color, 0.0) * max(1.0 - absorption_color, 0.0);
    Volume = scatter_coeff * density * henyey_greenstein(Anisotropy) +
             absorption_coeff * density * absorption();
  }

  /* Compute emission. */
  float emission_strength = max(EmissionStrength, 0.0);
  float blackbody_intensity = BlackbodyIntensity;

  if (emission_strength > 1e-5) {
    Volume += emission_strength * EmissionColor * emission();
  }

  if (blackbody_intensity > 1e-3) {
    float T = Temperature;

    /* Add temperature from attribute if available. */
    float temperature;
    if (getattribute(TemperatureAttribute, temperature)) {
      T *= max(temperature, 0.0);
    }

    T = max(T, 0.0);

    /* Stefan-Boltzman law. */
    float T4 = (T * T) * (T * T);
    float sigma = 5.670373e-8 * 1e-6 / M_PI;
    float intensity = sigma * mix(1.0, T4, blackbody_intensity);

    if (intensity > 1e-5) {
      color bb = blackbody(T);
      float l = luminance(bb);

      if (l != 0.0) {
        bb *= BlackbodyTint * intensity / l;
        Volume += bb * emission();
      }
    }
  }
}