Next: Image Texturing
- blotch BlendFactor surface
Produces a mildly interesting blotchy-looking surface.
BlendFactor is used to control the interpolation between
the default surface characteristics and the characteristics of
the given surface. A value of 0 results in a roughly 50-50 mix
of the two surfaces. Higher values result in a greater portion of
the default surface characteristics while lower values result in a greater
portion of the blotch surface.
Using an image texture applied to the ``bump'' component offers a more
direct way to control the modification of surface normals (see below).
- bump scale
Apply a random bump map. The point of intersection is passed to
The returned normalized vector is weighted by scale
and the result is added to the normal vector at the point of intersection.
- checker <Surface>
Applies a 3D checkerboard texture. Every point that falls within an
``even'' unit cube will be assigned the characteristics of the named surface
applied to it, while points that fall within ``odd'' cubes will have
its usual surface characteristics. Be wary of strange effects due
to roundoff error that occur when a planar checkered surface lies
in a plane of constant integral value (e.g., z=0) in texture space.
In such cases,
simply translate the texture to ensure that the planar surface is not
coincident with an integral plane in texture space
(e.g., translate 0 0 0.1).
- cloud scale H octaves cthresh lthresh tscale
This texture is a variant on Geoff Gardner's ellipsoid-texturing
algorithm. It should be applied to unit spheres centered
at the origin. These spheres may, of course, be transformed
at will to form the appropriately-shaped cloud or tree.
A sample of normalized fBm (see the
fbm texture) is generated
at the point of intersection. This sample is used to
modulate the surface transparency. The final transparency
if a function of the sample value, the
the proximity of the point of intersection to the edge of
the sphere (as seen from the ray origin), and three parameters
to control the overall ``density.'' The proximity of the point
to the sphere edge is determined by evaluating a limb function,
which varies from 0 on the limb to 1 at the center of the sphere.
- fbm offset scale H octaves thresh
Generate a sample of discretized fractional Brownian motion (fBm) and
uses it to scale the diffuse and ambient component of an object's surface.
Scale is used to scale the value
returned by the fBm function. Offset allows one to control the minimum
value of the fBm function. H is the Holder exponent
used in the fBm function (a value of 0.5 works well). is
used to control lacunarity, and specifies the the frequency
difference between successive samples of the fBm basis function (a
value of 2.0 will suffice). Octaves specifies the number of
octaves (samples) to take of the fBm basis function (in this case, Noise()).
Between five and seven octaves usually works well. Thresh is used
to specify a lower bound on the output of the fBm function. Any
value lower than thresh is set to zero.
If a colormap is named, a 256-entry colormap is read from the named
file, and the sample of fBm is scaled by 255 and is used as an index into
the colormap. The resulting colormap entry
is used to scale the ambient and diffuse components of the
- fbmbump offset scale H octaves
Similar to the fbm texture. Rather than modifying the color of
a surface, this texture acts as a bump map.
- gloss glossiness
Gives reflective surfaces a glossy appearance. This texture perturbs
the object's surface normal such that the normal ``samples'' a cone of
unit height with radius 1. - glossiness. A value of 1 results
in perfect mirror-like reflections, while a value of 0 results
in extremely fuzzy reflections. For best results, jittered sampling
should be used to render scenes that make use of this texture.
- marble [colormap]
Gives a surface a marble-like appearance. The texture is implemented as
roughly parallel alternating veins of marble, each of which is
separated by 1/7 of a unit and runs perpendicular to the Z axis.
If a colormap is named, the surface's ambient and diffuse colors
will be scaled using the RGB values in the colormap. If no colormap is
given, the diffuse and ambient components are simply scaled by the
value of the marble function. One may transform the texture to
control the density and orientation of the marble veins.
- sky scale H octaves cthresh ltresh
Similar to the fbm texture. Rather than modifying the
color of a surface, this texture modulates its transparency.
cthresh is the value of the fBm function above
which the surface is totally opaque. Below lthresh,
the surface is totally transparent.
Mapping functions are described below.
- stripe <Surface> size bump <Mapping>
Apply a ``raised'' stripe pattern to the surface.
The surface properties used to color the stripe are those
of the given surface. The width of the stripe, as compared
to the unit interval, is given by size. The magnitude
of bump controls the extent to which the bump appears
to be displaced from the rest of the surface. If negative,
the stripe will appear to
sink into the surface; if positive, it will appear to stand
out of the surface.
The gradient texture is used to blend two surfaces
Gives a surface a wood-like appearance. The feature size of this texture
is approximately 0.01 of a unit, making it often necessary to
scale the texture in order to achieve the desired appearance.
The default is to blend between two planes, starting at z = 0 and
stopping at z = 1. The default is a linear blend between planes so
that at z = 0.75 the surface will be
0.25*surf1 + 0.75*surf2.
- gradient <Surface1> <Surface2> [shape] [start [stop]] [type] [random]
This texture blends the two surfaces between two shapes in space.
The shape option specifies the "shape" of the volume to which the texture
will be applied. The default planar designates that the blend will be
between two planes perpendicular to z axis. radial designates that the
blend will be between two cylinders parallel to the z axis. spherical
designates that the blend will be between two spheres centered at the origin.
start and em stop define the starting and stopping distances for the
For the planar designation, the gradient will be applied from the z =
start to the z = stop planes.
For the radial designation, the gradient will be applied from the cylinders
r = start to r = stop where r equals the distance
from the z axis.
For the spherical designation, the gradient will be applied for the spheres
r = start to r = stop where r equals the distance
from the origin.
The type specifies the type of blend.
The default planar will produce a linear blend between the two surfaces.
log will produce a logarithmic looking blend where the first surface is
quickly changed to the second.
revlog will produce the opposite of log and will slowly change the
first surface to the second.
random produces a blotchy gradient texture that is similar to the
- mount colormap Turb Slope
This texture is a simple means of mapping a texture map onto a
heightfield in a way that is dependent upon the "altitude" of the
point in question and the "slope" at the point in question. The
texture computes an index into the colormap based on the Z value of
the point of intersection and the Z component of the normal at that
Turb is a scalar that is used to control how much 'randomness' is
thrown into the mix.
Next: Image Texturing
Jelle van Zeijl (email@example.com)
Wed Jun 15 16:19:08 MET DST 1994