blender/intern/cycles/kernel/svm/svm_fresnel.h

/*
 * 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.
 */

CCL_NAMESPACE_BEGIN

/* Fresnel Node */

ccl_device void svm_node_fresnel(
    ShaderData *sd, float *stack, uint ior_offset, uint ior_value, uint node)
{
  uint normal_offset, out_offset;
  decode_node_uchar4(node, &normal_offset, &out_offset, NULL, NULL);
  float eta = (stack_valid(ior_offset)) ? stack_load_float(stack, ior_offset) :
                                          __uint_as_float(ior_value);
  float3 normal_in = stack_valid(normal_offset) ? stack_load_float3(stack, normal_offset) : sd->N;

  eta = fmaxf(eta, 1e-5f);
  eta = (sd->flag & SD_BACKFACING) ? 1.0f / eta : eta;

  float f = fresnel_dielectric_cos(dot(sd->I, normal_in), eta);

  stack_store_float(stack, out_offset, f);
}

/* Layer Weight Node */

ccl_device void svm_node_layer_weight(ShaderData *sd, float *stack, uint4 node)
{
  uint blend_offset = node.y;
  uint blend_value = node.z;

  uint type, normal_offset, out_offset;
  decode_node_uchar4(node.w, &type, &normal_offset, &out_offset, NULL);

  float blend = (stack_valid(blend_offset)) ? stack_load_float(stack, blend_offset) :
                                              __uint_as_float(blend_value);
  float3 normal_in = (stack_valid(normal_offset)) ? stack_load_float3(stack, normal_offset) :
                                                    sd->N;

  float f;

  if (type == NODE_LAYER_WEIGHT_FRESNEL) {
    float eta = fmaxf(1.0f - blend, 1e-5f);
    eta = (sd->flag & SD_BACKFACING) ? eta : 1.0f / eta;

    f = fresnel_dielectric_cos(dot(sd->I, normal_in), eta);
  }
  else {
    f = fabsf(dot(sd->I, normal_in));

    if (blend != 0.5f) {
      blend = clamp(blend, 0.0f, 1.0f - 1e-5f);
      blend = (blend < 0.5f) ? 2.0f * blend : 0.5f / (1.0f - blend);

      f = powf(f, blend);
    }

    f = 1.0f - f;
  }

  stack_store_float(stack, out_offset, f);
}

CCL_NAMESPACE_END