Quote:Original post by discman1028
I realize why they chose [-1, 1] as the mapping for what they call the "pseudodepth", since the range provides a good dynamic range of depth values, since the "pseudodepth" is not linear. But why must it be mapped to [0, 1] before it is stored in the depth buffer?

It's just a convention I imagine, so that you have all non-negative values for the coordinates. They could just have easily made the Z-range in NDC be [0,1] instead of [-1,1] and avoided this extra transformation, but that's just the way things are :)

Quote:2) Am I correct that Z and W do not matter once we are in NDC (IF I don't care about depth buffering)?

I think so. There's a well known trick when rendering skyboxes last (to avoid fillrate waste on something that is probably barely visible a lot of the time) that makes use of this.

1. Clear depth buffer to 1
2. Render scene without skybox (so all parts of scene that the sky will fill have a depth of 1 [as they are untouched])
3. Set ZFunc to less or equal & turn off z writes
4. Render the skybox, but use a vertex shader that places the clip space z co-ord into w, so that after the post-proj divide z will always equal ~1

When I switched between the traditional & new technique, there seemed to be a very slight discrepancy (I was toggling between the two using a key press) but it was virtually unnoticeable. It was like changing between 89 and 90 fov or something. Maybe I had some other variable that changed between the techniques.

Given what I observed, I would say that the depth buffer does indeed store z/w. It's not the easiest thing to understand, really.

Yes, the depth buffer stores Z/W, unless otherwise modified by the fragment shader. This is one of the reasons why you experience Z-fighting if your near/far parameters are ill-conditioned, since Z/W is non-linear and all your precision is near the viewer while fragments far away from the viewer have to fight for those precision bits.

Quote:1. Clear depth buffer to 1
2. Render scene without skybox (so all parts of scene that the sky will fill have a depth of 1 [as they are untouched])
3. Set ZFunc to less or equal & turn off z writes
4. Render the skybox, but use a vertex shader that places the clip space z co-ord into w, so that after the post-proj divide z will always equal ~1

You might be safer using the stencil buffer so you don't have to rely on imprecise division and comparison. But that's just me :)