title: OpenGL Shading Language backwards compatibility
body: <p>I've noticed that my GLSL shaders are not compilable when the GLSL version is lower than 130. </p>
  
  <p>What are the most critical elements for having a backward compatible shader source? I don't want to have a full backward compatibility, but I'd like to understand the main guidelines for having simple (forward compatible) shaders running on GPU with GLSL lower than 130.</p>
  
  <p>Of course the problem could be solved with the preprocessor</p>
  
  <pre><code>#if __VERSION__ &lt; 130
  #define VERTEX_IN attribute
  #else
  #define VERTER_IN in
  #endif
  </code></pre>
  
  <p>But there probably many issues that I ignore.</p>