vpSetMaterial - set material properties
vpSetMaterial(vpc, material, property, surface_side, r, g, b)
double r, g, b;
vpc VolPack context from vpCreateContext.
A constant specifying a particular material number
(VP_MATERIAL0, VP_MATERIAL1, ..., VP_MATERIAL5).
A constant specifying one material property (VP_AMBIENT,
VP_DIFFUSE, VP_SPECULAR or VP_SHINYNESS).
A constant specifying which side of the material surface the
properties apply to (VP_EXTERIOR, VP_INTERIOR or VP_BOTH_SIDES).
r, g, b
RGB components of the color associated with the property. For
VP_SHINYNESS, g and b are not used.
vpSetMaterial is used to set the properties of a material type. Each
voxel may be composed of a mixture of several different material types,
as described in vpSetLookupShader(3). Each material type has its own
color and light reflection properties. The properties are used as
parameters to the Phong shading equation for computing the color of the
material given a set of light sources and a viewing direction (see
To initialize the material parameters, call vpSetMaterial for each
property of each material type to be used. The total number of
materials is specified as an argument to vpSetLookupShader. The first
material is specified by the constant VP_MATERIAL0, the second is
VP_MATERIAL1, and so on.
The VP_AMBIENT property specifies the RGB ambient light coefficients of
the material. This term represents the intensity of background light
reflected by the material. Each of the RGB components specifies the
coefficient for the corresponding light basis function. The values of
the coefficients should be in the range 0.0-1.0. Default: 0.1
The VP_DIFFUSE property specifies the RGB diffuse light coefficients of
the material. This term represents the fraction of incident light
intensity that is reflected diffusely (with a dull, matte appearance).
The values of the coefficients should be in the range 0.0-1.0.
The VP_SPECULAR property specifies the RGB specular light coefficients
of the material. This term represents the fraction of incident light
intensity that is reflected specularly (with a shiny, mirror-like
appearance). The values of the coefficients should be in the range
0.0-1.0. Default: 0.5
The VP_SHINYNESS property specifies a single exponent that modifies the
spread of specular highlights. The higher the number, the smaller and
more intense the specular highlights. The exponent is specified with
the r argument and can have any value; the generally-useful range is
1.0 to 100.0. The g and b arguments are ignored for this property.
The surface_side argument specifies which side of the material surface
the properties apply to. By default, the "interior" side of a voxel is
the side in the direction of the surface normal. During rendering, if
the normal points closer to the direction of the viewer than the
opposite of the normal then the viewer is looking at the exterior side
of the voxel rather than the interior. Different material parameters
can be applied to the two surface sides by calling vpSetMaterial
separately for each side. The option VP_BOTH_SIDES allows the same
property to be set for both sides with only one function call. It is
possible to reverse the definition of interior and exterior sides by
calling vpEnable with the VP_REVERSE_SURFACE_SIDES option.
Voxels are shaded using the following equation:
I = A + L * (D * n_dot_l + S * pow(n_dot_h, E))
I intensity for one color channel
A ambient intensity coefficient
D diffuse reflection coefficient
S specular reflection coefficient
L light intensity
n_dot_l dot product of normal and light vectors
n_dot_h dot product of normal and highlight vectors
This equation is evaluated separately for each color channel. If
multiple light sources are enabled an additional term identical to the
second term above is added for each light source (with different values
for L, n_dot_l and n_dot_h corresponding to the particular light
Information about the current material properties can be retrieved with
the following state variable codes (see vpGeti(3)): VP_MATERIAL_COUNT,
The normal return value is VP_OK. The following error return values
Either the material number or the RGB components are invalid.
Either the surface_side or property arguments are invalid.
VolPack(3), vpCreateContext(3), vpSetLookupShader(3), vpShadeTable(3),