wined3d: Take abs() of vertex z coordinate as FFP fog coordinate and remove oFog clamp for vertex shaders

[Joachim Priesner]

Hi,

thanks for testing -- unfortunately I can only test on one Nvidia system and on VMware.

> I have tested your patches on my various systems. I have replaced
> C_IGNORE in the d3d8 test with C_FOGGED. The test passes on Nvidia
> cards, but fails (also in d3d9) on my AMD cards. As far as I can see
> AMD cards clamp the fog coord.

Okay, so the fog clamp is not wrong. I'll be happy to re-add it and modify the test so it accepts both variants.

> I haven't quite understood yet what you're doing with quad2/quad3, so
> I can't comment on the code yet.

These are not strictly necessary, but the idea is to make sure quad1 being fully fogged when using vertex fog is not some kind of artifact. Basically, I "split" quad1 at z=0, so quad2/quad3 should have a gradient FOGGED -> UNFOGGED -> FOGGED.

If you think they do more harm than good by cluttering the test, I can remove it without the abs() bug not being detected.

Joachim