vpNormalIndex, vpNormal - encode/decode a surface normal vector
vpNormalIndex(nx, ny, nz)
- double nx, ny, nz;
vpNormal(n, nx_ptr, ny_ptr, nz_ptr)
- int n;
- double *nx_ptr, *ny_ptr, *nz_ptr;
- X component of surface normal vector.
- Y component of surface normal vector.
- Z component of surface normal vector.
- Encoded surface normal vector.
- Pointer to storage for returning X component of surface normal
- Pointer to storage for returning Y component of surface normal
- Pointer to storage for returning Z component of surface normal
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
(or one of the higher-level normal vector computation
shading routines or lookup tables are not required to use encoded normal
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.
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
always returns a valid encoded normal vector.
normally returns the value VP_OK. The following return value is
- The encoded normal vector is invalid.
VolPack(3), vpVolumeNormals(3), vpScanlineNormals(3)