vpSetLight - set lighting properties
vpSetLight(vpc, light_num, property, n0, n1, n2)
double n0, n1, n2;
vpc VolPack context from vpCreateContext.
A constant specifying a particular light source (VP_LIGHT0,
VP_LIGHT1, ..., VP_LIGHT5).
A constant specifying one lighting property (VP_COLOR or
n0, n1, n2
Components of an RGB color (for VP_COLOR) or a direction vector
vpSetLight is used to set the properties of a light source. VolPack
currently only supports directional light sources: each light is
infinitely distant, so it can be fully characterized by a direction
vector and a color. The lighting properties are used by vpShadeTable
to compute the shading lookup table, which is then used to compute a
color for each voxel.
To initialize the lighting environment, call vpSetLight twice for each
light source which will be enabled. One call should set the RGB
components of the light color (by using the VP_COLOR code for the
property parameter), and one call should set the XYZ components of the
light direction vector (by using the VP_DIRECTION code for the property
parameter). The particular light source is specified with one of the
light source codes defined in volpack.h: VP_LIGHT0, VP_LIGHT1, ...,
VP_LIGHT5. In the current implementation, at most six light sources
may be specified.
The RGB components of a light color should be numbers in the range 0.0
(zero intensity) to 1.0 (full intensity). For grayscale renderings
only the first (red) component is used and the other components may be
set to any legal value. The default is white light (1.0, 1.0, 1.0).
The light direction vector points from the light source towards the lit
object. It is transformed by the current contents of the modeling
matrix (see vpCurrentMatrix). This allows the direction vector to be
specified in an arbitrary coordinate system, provided the current
modeling matrix properly transforms the vector into world coordinates.
The default is the vector (1,1,1).
Each light source contributes to the shading computation only if it is
enabled by calling vpEnable. By default, VP_LIGHT0 is enabled and all
other lights are disabled. The more light sources that are enabled,
the longer it takes to precompute the contents of the shading lookup
One additional property of the light sources can be set with vpEnable:
VP_LIGHT_BOTH_SIDES. With this option enabled each light source shines
in two opposing directions, as if there were two light sources facing
each other with opposite direction vectors. No additional computation
is required when this option is enabled.
Information about the current lighting properties can be retrieved with
the following state variable codes (see vpGeti(3)):
The normal return value is VP_OK. The following error return values
The light number is invalid or exceeds an implementation limit.
The light direction vector is a zero vector.
The RGB color components are out of range.
The property argument is invalid.
VolPack(3), vpCreateContext(3), vpSetLookupShader(3), vpShadeTable(3),