text: /*
   * 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
   */
   
  float fresnel_dielectric_cos(float cosi, float eta)
  {
  	/* compute fresnel reflectance without explicitly computing
  	 * the refracted direction */
  	float c = fabs(cosi);
  	float g = eta * eta - 1 + c * c;
  	float result;
  
  	if (g > 0) {
  		g = sqrt(g);
  		float A = (g - c) / (g + c);
  		float B = (c * (g + c) - 1) / (c * (g - c) + 1);
  		result = 0.5 * A * A * (1 + B * B);
  	}
  	else
  		result = 1.0;  /* TIR (no refracted component) */
  
  	return result;
  }
  
  color fresnel_conductor(float cosi, color eta, color k)
  {
  	color cosi2 = color(cosi * cosi);
  	color one = color(1, 1, 1);
  	color tmp_f = eta * eta + k * k;
  	color tmp = tmp_f * cosi2;
  	color Rparl2 = (tmp - (2.0 * eta * cosi) + one) /
  	               (tmp + (2.0 * eta * cosi) + one);
  	color Rperp2 = (tmp_f - (2.0 * eta * cosi) + cosi2) /
  	               (tmp_f + (2.0 * eta * cosi) + cosi2);
  	return (Rparl2 + Rperp2) * 0.5;
  }
  
  