   GPU Volume Rendering 2
  I notice that my volume rendering speed depends on the viewpoint.  This should be expected a little bit since the proxy polygons depend on the viewpoint, but I am getting pretty drastic differences (80-300 FPS differences).1) I get the best frame rate when I'm looking "head-on" the volume, that is the view plane is parallel with the (width x height planes of the volume).2) I get the worst frame rate, when I'm looking at the side of the volume (height x depth plane).I don't know too much about hardware, but in case (2), when a proxy polygon is rendered, the neighboring texels are not "nearby" but instead an entire SlicePitch needs to be skipped.  I'm not sure if that's a big deal or not.   
  I'm not entirely sure as to how you're rendering this cube, but if I had to guess, you're experiencing some nasty texture cache miss issues. Since looking at the side you're going against the grain of the texture, but looking head-on, the memory accesses are more cache friendly since they're being sampled in a way that the card expects it to be.   ;  That's pretty much what I was guessing, too.  Can any experts confirm?The volume is 512x512x256.   