def replace_include(source)
      source.gsub!(/^#include\s+<([^>]*)>/) do
        replace_include File.read(File.expand_path("#{$1}.glsl", INCLUDE_PATH))
      end

      source.gsub(/^#include\s+"([^"]*)"/) do
        replace_include File.read($1)
      end
    end
def replace_include(source)
      source.gsub!(/^#include\s+<([^>]*)>/) do
        replace_include File.read(File.expand_path("#{$1}.glsl", INCLUDE_PATH))
      end

      source.gsub(/^#include\s+"([^"]*)"/) do
        replace_include File.read($1)
      end
    end
Recursively replace #include.

 * Replace '#include <rand>' with the contents of include/rand.glsl
 * Replace '#include "/home/spooner/my_shader_functions/frog.glsl"' with the contents of that file.

 @return [String] Source code that has been expanded.