Using a vertex shader, is it possible to send out the z value of
vertices to a pixel shader which then displays the values as a color,
even if the scene has fixed function fog?

Currently I am doing the above to produce a position texture, which I
then use as the basis for a Z position map. When fog is off,
everything behaves as expected. Objects which are close to the camera
are one color, and those farther away interpolate to another.
However, as soon as I enable the fog renderstate, the values are no
longer accurate.

I have read that pixel fog cannot be used with vertex shaders, however
I get this result just by enabling fixed function fog. I then tested
specifically for vertex and pixel fog, and both produced whacky
results.

Any insight is appreciated. Thanks in advance.

[Please do not mail me a copy of your followup]

Noley Edge gmail.com> spake the secret code
<4feae760-66fc-4d8b-b770-05e608c6bc27@d45g2000hsc.googlegroups.com> thusly:

There are two kinds of fixed function fog: vertex fog and pixel fog.
If you use a vertex shader, you can't use fixed-function vertex fog
(you have to compute the per-vertex fog factor in your shader).

IIRC, fixed-function pixel fog can be used with a vertex shader,
providing you're not also using a pixel shader.

On Jun 6, 6:40 pm, legalize+jee...@mail.xmission.com (Richard
[Microsoft Direct3D MVP]) wrote:

[Please do not mail me a copy of your followup]

Noley Edge gmail.com> spake the secret code
<49bebd17-2fa7-4c48-8c82-d4d3a36dda57@m44g2000hsc.googlegroups.com> thusly:

Go with what the book says then. When I write stuff for the book, its
because I've researched it and identified the corner cases. When I
post to the net, its usually just form memory, which is subject to
corruption :-)

On Jun 10, 3:14 pm, legalize+jee...@mail.xmission.com (Richard
[Microsoft Direct3D MVP]) wrote:

On Jun 10, 4:59 pm, Noley Edge gmail.com> wrote:

[Please do not mail me a copy of your followup]

Noley Edge gmail.com> spake the secret code
<77b45b07-a70c-442d-a539-97e4ef4170df@b1g2000hsg.googlegroups.com> thusly:

Are you going from what HAL does or what REF does? With tricky
manipulation of the fog states here combined with shaders you could
just be exposing a driver bug. REF is supposed to give you the
definitive answer (and to be honest, I've not encountered any bugs in
REF before).

Thanks! I'm glad its helpful to you; that's why I wrote it.