Ubuntu Manpage: vpSetMaterial - set material properties

Provided by: libvolpack1-dev_1.0b3-9_amd64

NAME

       vpSetMaterial - set material properties

SYNOPSIS

       #include <volpack.h>

       vpResult
       vpSetMaterial(vpc, material, property, surface_side, r, g, b)
           vpContext *vpc;
           int material;
           int property;
           int surface_side;
           double r, g, b;

ARGUMENTS

       vpc    VolPack context from vpCreateContext.

       material
              A  constant  specifying  a  particular material number (VP_MATERIAL0, VP_MATERIAL1,
              ..., VP_MATERIAL5).

       property
              A constant specifying one material property (VP_AMBIENT, VP_DIFFUSE, VP_SPECULAR or
              VP_SHINYNESS).

       surface_side
              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.

DESCRIPTION

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 vpShadeTable(3)).

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. Default: 0.4

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. Default:
10.0

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
E shinyness
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 source).

STATE VARIABLES

       Information about the current material properties can  be  retrieved  with  the  following
       state variable codes (see vpGeti(3)): VP_MATERIAL_COUNT, VP_REVERSE_SURFACE_SIDES

ERRORS