title: Determining if a polygon is inside the viewing frustum
body: <p>here are my questions. I heard that opengl ignores the vertices which are outside the viewing frustum and doesn't consider them in rendering pipeline. Recently I ran into a same post that said you should check this your self and if a point is not inside, it is you duty to find out not opengl's! Now,</p>
  
  <ol>
  <li>Is this true about opengl? does it understand if a point is not inside, and not to render it?</li>
  <li>I am developing a grass scene which has about 4000 grasses on rectangles. I have awful FPS, and the only solution I came up was to decide which grasses are inside the viewport and then only render them! My question here is that what solution is best for me to find out which rectangle is not inside or which one is?</li>
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  <p>Please consider that my question is not about points mainly but about rectangles. Also I need to sort the grasses based on their distance, so it is better if native on client side memory.</p>
  
  <p>Please let me know if there are any effective and real-time ways to find out if any given mesh is inside or outside the frustum. Thanks.</p>