RE: [Algorithms] normal map mipmaps

[Tom F. <to...@mu...>]

Oh, yes - bigger kernels are better. I was just throwing that one into =
code
because it's quick to type :-) It's not actually very good because it =
gives
an off-by-half error.

I usually use this one:
>     0 -1 0
>     0  0 0
>     0  1 0
...and the corresponding one.

I have thought about using other kernels, because this one is a bit =
harsh,
and is very sensitive to the fact that there are usually only 8 bits of
precision in the bumpmap, but never got around to experimenting with =
any. I
might give your other two a go - they look promising.


Tom Forsyth - purely hypothetical Muckyfoot bloke.

This email is the product of your deranged imagination,
and does not in any way imply existence of the author.

> -----Original Message-----
> From: Evan Hart [mailto:eh...@at...]
> Sent: 13 February 2002 20:07
> To: Algorithms
> Subject: RE: [Algorithms] normal map mipmaps
>=20
>=20
>=20
> Actually, this brings up another good question of what is the=20
> best way to
> compute the normals from the bumpmap?=20
>=20
> I notice that you are only using 3 height map texels to=20
> compute a normal. I
> typically use  4 or 8. What are the tradeoffs of the=20
> different filters, and
> do they effect how it mipmaps?
>=20
> Here are your filter kernels:
>=20
>   X:
>      0 -1 0
>      0  1 0
>      0  0 0
>=20
>   Y:
>      0 0  0
>      0 1 -1
>      0 0  0
>=20
> The ones I typically use are:
>=20
>   X:
>     0 -1 0
>     0  0 0
>     0  1 0
>   or
>     -1 -2 -1
>      0  0  0
>      1  2  1
>=20
>   Y:
>     0 0 0
>     1 0 -1
>     0 0 0
>   or
>     1 0 -1
>     2 0 -2
>     1 0 -1
>=20
>=20
>=20
> -----Original Message-----
> From: Tom Forsyth [mailto:to...@mu...]
> Sent: Wednesday, February 13, 2002 1:09 PM
> To: Ignacio Casta=F1o; Algorithms
> Subject: RE: [Algorithms] normal map mipmaps
>=20
>=20
> There is no "right" way as far as I know. It's a big research=20
> topic. If you
> find a solution, could you let the DX9 chaps know - it's incredibly
> important for displacement mapping :-)
>=20
> You're calculating the normal mipmaps wrong. Remember that=20
> lower levels not
> only have fewer pixels, but they are _further apart_. So on=20
> the top level
> you would do this:
>=20
> Vec3 norm;
> norm.x =3D height[x][y] - height[x][y+1];
> norm.y =3D height[x][y] - height[x+1][y];
> norm.z =3D z_scale;
> norm =3D norm.Normalise();
>=20
>=20
> But on the next level down, you need to do:
>=20
>=20
> Vec3 norm;
> norm.x =3D height[x][y] - height[x][y+1];
> norm.y =3D height[x][y] - height[x+1][y];
> norm.z =3D z_scale * 2.0f;
> norm =3D norm.Normalise();
>=20
>=20
> Otherwise you will get images that are far too crisp.
>=20
>=20
> Tom Forsyth - purely hypothetical Muckyfoot bloke.
>=20
> This email is the product of your deranged imagination,
> and does not in any way imply existence of the author.
>=20
>=20
>=20
> > -----Original Message-----
> > From: Ignacio Casta=F1o [mailto:cas...@ya...]
> > Sent: 13 February 2002 17:57
> > To: Algorithms
> > Subject: [Algorithms] normal map mipmaps
> >=20
> >=20
> > Hi,
> > which is the way of correctly calculating normal maps=20
> > mipmaps? I've been
> > doing that by turning the bumpmap into a normalmap,=20
> > calculating the mipmaps
> > and renormalizing them. That worked pretty well, but someone=20
> > mentioned that
> > instead of that you should calculate the mipmaps of the=20
> > bumpmap and then
> > turn them into normalmaps, and that doesn't look very good,=20
> > the normal maps
> > of the mipmap chain are very differnt, smaller mipmaps look=20
> > sharper and
> > that's very noticeable. Does somebody have any suggestion?
> >=20
> > Thanks in advance,
> >=20
> > Ignacio Casta=F1o
> > ca...@as...
> >=20
> >=20
> >=20
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