NAME
vpSetVoxelSize - define the size of a voxel
SYNOPSIS
#include <volpack.h>
vpResult
vpSetVoxelSize(vpc, bytes_per_voxel, num_voxel_fields,
num_shade_fields, num_classify_fields)
vpContext *vpc;
int bytes_per_voxel;
int num_voxel_fields;
int num_shade_fields;
int num_classify_fields;
ARGUMENTS
vpc VolPack context from vpCreateContext.
bytes_per_voxel
Size of one voxel in bytes.
num_voxel_fields
Number of fields in a voxel.
num_shade_fields
Number of voxel fields that are arguments to the shading
function.
num_classify_fields
Number of voxel fields that are arguments to the opacity
transfer function.
DESCRIPTION
vpSetVoxelSize is used to define the size in bytes and the number of
fields in a voxel. Each voxel field is analogous to a field in a C
structure and the contents of each field is user-defined. See the
vpSetVoxelField function (vpSetVoxelField(3)) for setting the size and
offset of each field. vpSetVoxelSize should be called before
vpSetVoxelField and before any functions that access the contents of a
voxel.
Typically, some of the voxel fields are used as arguments to a shading
function and some (possibly the same) fields are used as arguments to
an opacity transfer function (for classification). The fields that are
used for shading should come first, i.e. they should have the smallest
offsets, followed by any fields that are only used for classification.
The classification fields can then be stripped off to save space during
the precomputation stage for the fast rendering algorithm. The
parameter num_shade_fields indicates the number of fields (starting
from the first) that must not be stripped off.
The parameter num_clsfy_fields indicates the total number of fields
that are used as parameters to the opacity transfer function. These
fields do not necessarily have to be contiguous, although any fields
that are not also used for shading should be the last fields in the
voxel.
If the call to vpSetVoxelSize succeeds, any existing precomputed volume
data structures in the context are destroyed.
STATE VARIABLES
The current voxel size parameters can be retrieved with the following
state variable codes (see vpGeti(3)): VP_BYTES_PER_VOXEL,
VP_VOXEL_FIELD_COUNT, VP_SHADE_FIELD_COUNT, VP_CLASSIFY_FIELD_COUNT.
ERRORS
The normal return value is VP_OK. The following error return values
are possible:
VPERROR_LIMIT_EXCEEDED
The number of voxel fields exceeds the implementation limit.
This limit can be increased by editing volpack.h and recompiling
the library.
VPERROR_BAD_VALUE
Either num_clsfy_fields or num_shade_fields is out of range.
SEE ALSO
VolPack(3), vpCreateContext(3), vpSetVoxelField(3)