Provided by: libvolpack1-dev_1.0b3-10_amd64 
NAME
vpSetLight - set lighting properties
SYNOPSIS
#include <volpack.h>
vpResult
vpSetLight(vpc, light_num, property, n0, n1, n2)
vpContext *vpc;
int light_num;
int property;
double n0, n1, n2;
ARGUMENTS
vpc VolPack context from vpCreateContext.
light_num
A constant specifying a particular light source (VP_LIGHT0, VP_LIGHT1, ..., VP_LIGHT5).
property
A constant specifying one lighting property (VP_COLOR or VP_DIRECTION).
n0, n1, n2
Components of an RGB color (for VP_COLOR) or a direction vector (for VP_DIRECTION).
DESCRIPTION
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 table.
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.
STATE VARIABLES
Information about the current lighting properties can be retrieved with the following state variable
codes (see vpGeti(3)): VP_LIGHT_BOTH_SIDES.
ERRORS
The normal return value is VP_OK. The following error return values are possible:
VPERROR_LIMIT_EXCEEDED
The light number is invalid or exceeds an implementation limit.
VPERROR_SINGULAR
The light direction vector is a zero vector.
VPERROR_BAD_VALUE
The RGB color components are out of range.
VPERROR_BAD_OPTION
The property argument is invalid.
SEE ALSO
VolPack(3), vpCreateContext(3), vpSetLookupShader(3), vpShadeTable(3), vpGetLight(3)