title: iPhone picking/unproject when in landscape view (projection matrix is rotated)
body: <p>I am trying to get 'picking' working in a 3D scene, where the view is rotated such that the iPhone is being held in a landscape mode. I'm using OpenGL ES 2.0 (so all shaders, no fixed-function pipeline).</p>
  
  <p>I'm performing the unproject from within the rendering code and immediately drawing the resulting ray using GL_LINES (ray only gets calculated the 1st time that I touch the screen, so afterwards I can move the camera around to observe the resulting line from various angles).</p>
  
  <p>My unproject code/call is fine (lots of examples of gluUnproject online). My matrix-inversion code is fine (even compared with excel for a few matrices). However, the resulting ray is off by at least 5-15 degrees from where I actually 'clicked' (in the Simulator it really is a click, so I'm expecting a lot more precision from the unproject).</p>
  
  <p>My view is rotated to landscape (after I create the perspective-projection matrix, I rotate it around the Z by -90 degrees; the aspect ratio remains at a portrait one). I believe that the problem with the math being off lies here.</p>
  
  <p>Does anyone have any experience doing picking/unprojection with specifically a landscape view?</p>