NAME
vpNormalIndex, vpNormal - encode/decode a surface normal vector
SYNOPSIS
#include <volpack.h>
int
vpNormalIndex(nx, ny, nz)
double nx, ny, nz;
vpResult
vpNormal(n, nx_ptr, ny_ptr, nz_ptr)
int n;
double *nx_ptr, *ny_ptr, *nz_ptr;
ARGUMENTS
nx X component of surface normal vector.
ny Y component of surface normal vector.
nz Z component of surface normal vector.
n Encoded surface normal vector.
nx_ptr Pointer to storage for returning X component of surface normal
vector.
ny_ptr Pointer to storage for returning Y component of surface normal
vector.
nz_ptr Pointer to storage for returning Z component of surface normal
vector.
DESCRIPTION
These two routines are used to convert surface normal vectors between
encoded and unencoded forms. An unencoded vector is described by its
three components (stored as double-precision floating point numbers) in
an orthogonal coordinate system. An encoded vector is described by a
single integer that is suitable for use as an index in a shading lookup
table. VolPack’s built-in shading routines require the use of surface
normal vectors encoded using vpNormalIndex (or one of the higher-level
normal vector computation routines, vpVolumeNormals or
vpScanlineNormals). User-defined shading routines or lookup tables are
not required to use encoded normal vectors.
vpNormalIndex computes an encoded vector from the components of an
unencoded vector. The vector must be normalized (nx*nx + ny*ny + nz*nz
= 1). The maximum possible value of an encoded normal is given by the
constant VP_NORM_MAX.
vpNormal computes the components of a vector from the encoded integer
form. The encoded normal has less resolution than the unencoded form,
so the vector computed by vpNormal may not be equal to the original
vector passed to vpNormalIndex.
ERRORS
vpNormalIndex always returns a valid encoded normal vector.
vpNormal normally returns the value VP_OK. The following return value
is possible:
VPERROR_BAD_VALUE
The encoded normal vector is invalid.
SEE ALSO
VolPack(3), vpVolumeNormals(3), vpScanlineNormals(3)