text: // ======================================================================== //
  // Copyright 2009-2018 Intel Corporation                                    //
  //                                                                          //
  // 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 "light.h"
  #include "../math/sampling.h"
  #include "../math/linearspace.h"
  
  namespace embree {
  
  struct AmbientLight
  {
    Light super;      //!< inherited light fields
  
    Vec3fa radiance;   //!< RGB color and intensity of light
  };
  
  
  // Implementation
  //////////////////////////////////////////////////////////////////////////////
  
  // XXX importance sampling is only done into the positive hemisphere
  // ==> poor support for translucent materials
  Light_SampleRes AmbientLight_sample(const Light* super,
                                      const DifferentialGeometry& dg,
                                      const Vec2f& s)
  {
    AmbientLight* self = (AmbientLight*)super;
    Light_SampleRes res;
  
    const Vec3fa localDir = cosineSampleHemisphere(s);
    res.dir = frame(dg.Ns) * localDir;
    res.pdf = cosineSampleHemispherePDF(localDir);
    res.dist = inf;
    res.weight = self->radiance * rcp(res.pdf);
  
    return res;
  }
  
  Light_EvalRes AmbientLight_eval(const Light* super,
                                  const DifferentialGeometry& dg,
                                  const Vec3fa& dir)
  {
    AmbientLight* self = (AmbientLight*)super;
    Light_EvalRes res;
  
    res.value = self->radiance;
    res.dist = inf;
    res.pdf = cosineSampleHemispherePDF(max(dot(dg.Ns, dir), 0.f));
  
    return res;
  }
  
  
  void AmbientLight_Constructor(AmbientLight* self,
                                const Vec3fa& radiance)
  {
    Light_Constructor(&self->super);
    self->radiance = radiance;
    self->super.sample = AmbientLight_sample;
    self->super.eval = AmbientLight_eval;
  }
  
  
  // Exports (called from C++)
  //////////////////////////////////////////////////////////////////////////////
  
  //! Create an ispc-side AmbientLight object
  extern "C" void *AmbientLight_create()
  {
    AmbientLight* self = (AmbientLight*) alignedMalloc(sizeof(AmbientLight));
    AmbientLight_Constructor(self, Vec3fa(1.f));
    return self;
  }
  
  //! Set the parameters of an ispc-side AmbientLight object
  extern "C" void AmbientLight_set(void* super,
                               const Vec3fa& radiance)
  {
    AmbientLight* self = (AmbientLight*)super;
    self->radiance = radiance;
  }
  
  } // namespace embree
  