// We want glsl to support some preprocess directives:
// just like: #ifdef...#endif, #include, #error, #warning, #pragma
//
// The following code snippet is an example.
std::string Shader::PreprocessIncludes(const std::string& source, const boost::filesystem::path& filename, int level /*= 0 */)
{
	PrintIndent();
	if(level > 32)
		LogAndThrow(ShaderException,"header inclusion depth limit reached, might be caused by cyclic header inclusion");
	using namespace std;

	static const boost::regex re("^[ ]*#[ ]*include[ ]+[\"<](.*)[\">].*");
	stringstream input;
	stringstream output;
	input << source;

	size_t line_number = 1;
	boost::smatch matches;

	string line;
	while(std::getline(input,line))
	{
		if (boost::regex_search(line, matches, re))
		{
			std::string include_file = matches[1];
			std::string include_string;

			try
			{
				include_string = Core::FileIO::LoadTextFile(include_file);
			} 
			catch (Core::FileIO::FileNotFoundException& e)
			{
				stringstream str;
				str <<  filename.file_string() <<"(" << line_number << ") : fatal error: cannot open include file " << e.File();
				LogAndThrow(ShaderException,str.str())
			}
			output << PreprocessIncludes(include_string, include_file, level + 1) << endl;
		}
		else
		{
			output << "#line "<< line_number << " \"" << filename << "\""  << endl;
			output <<  line << endl;
		}
		++line_number;
	}
	PrintUnindent();
	return output.str();
}