1vpNormalIndex(3)           Library Functions Manual           vpNormalIndex(3)
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NAME

6       vpNormalIndex, vpNormal - encode/decode a surface normal vector
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SYNOPSIS

9       #include <volpack.h>
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11       int
12       vpNormalIndex(nx, ny, nz)
13           double nx, ny, nz;
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15       vpResult
16       vpNormal(n, nx_ptr, ny_ptr, nz_ptr)
17           int n;
18           double *nx_ptr, *ny_ptr, *nz_ptr;
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ARGUMENTS

21       nx     X component of surface normal vector.
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23       ny     Y component of surface normal vector.
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25       nz     Z component of surface normal vector.
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27       n      Encoded surface normal vector.
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29       nx_ptr Pointer  to  storage for returning X component of surface normal
30              vector.
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32       ny_ptr Pointer to storage for returning Y component of  surface  normal
33              vector.
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35       nz_ptr Pointer  to  storage for returning Z component of surface normal
36              vector.
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DESCRIPTION

39       These two routines are used to convert surface normal  vectors  between
40       encoded  and  unencoded forms.  An unencoded vector is described by its
41       three components (stored as double-precision floating point numbers) in
42       an  orthogonal  coordinate system.  An encoded vector is described by a
43       single integer that is suitable for use as an index in a shading lookup
44       table.   VolPack's built-in shading routines require the use of surface
45       normal vectors encoded using vpNormalIndex (or one of the  higher-level
46       normal  vector  computation routines, vpVolumeNormals or vpScanlineNor‐
47       mals).  User-defined shading routines or lookup tables are not required
48       to use encoded normal vectors.
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50       vpNormalIndex  computes  an  encoded  vector  from the components of an
51       unencoded vector.  The vector must be normalized (nx*nx + ny*ny + nz*nz
52       =  1).  The maximum possible value of an encoded normal is given by the
53       constant VP_NORM_MAX.
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55       vpNormal computes the components of a vector from the  encoded  integer
56       form.   The encoded normal has less resolution than the unencoded form,
57       so the vector computed by vpNormal may not be  equal  to  the  original
58       vector passed to vpNormalIndex.
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ERRORS

61       vpNormalIndex always returns a valid encoded normal vector.
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63       vpNormal  normally returns the value VP_OK.  The following return value
64       is possible:
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66       VPERROR_BAD_VALUE
67              The encoded normal vector is invalid.
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SEE ALSO

70       VolPack(3), vpVolumeNormals(3), vpScanlineNormals(3)
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74VolPack                                                       vpNormalIndex(3)
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