RE: [Algorithms] view dependant fog error

[Tom F. <tom...@ee...>]

Indeed - see the docs on D3DRS_RANGEFOGENABLE for example.

However, fog is a special-cased hack (and not a very good one at that) =
that
will go away shortly and be entirely replaced by just doing whatever =
shader
instructions you feel like to get a similar effect.

TomF.

> -----Original Message-----
> From: gda...@li...=20
> [mailto:gda...@li...] On=20
> Behalf Of Ignacio Casta=F1o
> Sent: 23 April 2004 17:38
> To: gda...@li...
> Subject: Re: [Algorithms] view dependant fog error
>=20
>=20
> Hi Ian,
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> Depth fog is sometimes preferred over distance fog, because depth=20
> changes linearly along triangles, while distance does not. For this=20
> reason depth fog is independant of tesellation. Distance fog=20
> can cause=20
> artifacts on meshes with low tesselation or during lod changes. There=20
> are OpenGL extensions to switch between the two, and I wouldn't be=20
> surprised if Direct3D provided the same feature.
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> --=20
> Ignacio Casta=F1o
> cas...@ya...
>=20
>=20
>=20
> Ian McMeans wrote:
> > This is kind of a minor issue, but I thought maybe some=20
> people will be=20
> > interested in it and will fix it in their games. I've noticed it in=20
> > plenty of games, I'm sure other people have noticed it too.=20
> I searched=20
> > the archives in case this had been discussed before, and=20
> found nothing.
> > =20
> > The error is how the fog is view-direction-dependant. Look at the=20
> > central tower in this screenshot of ONS-Torlan:
> > http://img9.imageshack.us/my.php?loc=3Dimg9&image=3DShot00000.jpg=20
> > <http://img9.imageshack.us/my.php?loc=3Dimg9&image=3DShot00000.jpg>
> > =20
> > and then this screenshot, taken facing a slightly different=20
> direction:
> > http://img9.imageshack.us/my.php?loc=3Dimg9&image=3DShot00001.jpg=20
> > <http://img9.imageshack.us/my.php?loc=3Dimg9&image=3DShot00001.jpg>
> > =20
> > Now, my guess is that it's caused by how the fog is computed using=20
> > depth, and depth in turn is computed based on the view=20
> frustrum. And=20
> > when you're looking at something in the corner of your view=20
> frustrum,=20
> > then the fog is less intense there because the object=20
> you're looking at=20
> > is then further from the far plane. (Sorry if this=20
> explanation isn't too=20
> > clear).
> > =20
> > Is it just not worth fixing because it's a minor issue? I=20
> imagine you=20
> > could fix it by weighting the fog based on the view vector=20
> compared to=20
> > the lookat vector, but perhaps the cost in shader=20
> instructions isn't=20
> > worth the benefit in this case.
>=20
>=20
>=20
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