text: // Copyright (c) 2013-2014 Matthew Paul Reid
  
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  // THE SOFTWARE.
  
  #ifndef TEXTURE_PCF_H
  #define TEXTURE_PCF_H
  
  vec4 texturePcf2(sampler3D sampler, vec3 texcoord, vec3 halfTexelOffset)
  {
  	vec4 sum = vec4(0);
  	
  	for (int z = -1; z <= 1; z+=2)
  	{
  		for (int y = -1; y <= 1; y+=2)
  		{		
  			for (int x = -1; x <= 1; x+=2)
  			{
  				sum += texture(sampler, texcoord += halfTexelOffset * vec3(x, y, z));
  			}
  		}
  	}
  	return sum /= 8.0;
  }
  
  #endif