title: How to get world coordinates from screen coordinates in opengl es2.0?
body: <p>I am new to opengl. I am drawing a map in android using opengl ES2.0. When i touch on screen i am getting screen coordinates. i want these coordinates to be converted into world coordinates. The code i found through research is as follows:</p>
  
  <pre><code>vec3 UnProjectPoint( const vec3&amp; Point, const max4&amp; Projection, const mat4&amp; ModelView )
  {
      vec4 R( Point, 1.0f );
  
      R.x = 2.0f * R.x - 1.0f;
      R.y = 2.0f * R.y - 1.0f;
      R.y = -R.y;
  
      R.z = 1.0f;
  
      R = Projection.GetInversed() * R;
      R = ModelView.GetInversed() * R;
  
      return R.ToVec3();
  }
  </code></pre>
  
  <p>but android is not allowing me to use vec3 and vec4?
  I also use built in gluunproject function but this function is also not giving me correct results.</p>