.\" @(#)PEXGeoNormTriangleStrip.3 1.5 95/03/24 SMI;
.so man3/pex.macs
.TH PEXGeoNormTriangleStrip 3 "May 1995" "Solaris PEXlib Reference Manual" ""
.SH NAME
PEXGeoNormTriangleStrip - utility function
.SH SYNTAX
.HP
int PEXGeoNormTriangleStrip\^(\^unsigned int \fIfacet_attributes\fP, unsigned int \fIvertex_attributes\fP, int \fIcolor_type\fP, PEXArrayOfFacetData \fIfacet_data\fP, unsigned int \fIcount\fP, PEXArrayOfVertex \fIvertices\fP)
.SH PARAMETERS
.IP \fIfacet_attributes\fP 1i
A mask indicating the facet attributes provided.  It should contain the bit
.B PEXGANormal.
.IP \fIvertex_attributes\fP 1i
A mask indicating the vertex attributes provided.
.IP \fIcolor_type\fP 1i
The type of color data provided.
.IP \fIfacet_data\fP 1i
An array of facet data.  This function adds the geometric normals to this data.
.IP \fIcount\fP 1i
The number of vertices.
.IP \fIvertices\fP 1i
An array of vertices defining the triangle strip.
.SH RETURNS
Zero if successful; otherwise, one of the following:
.TP
.B PEXBadPrimitive
A normal cannot be computed for one or more triangles in the strip.
.SH DESCRIPTION
.\" indexing
.IX PEXGeoNormTriangleStrip
.IX "Utility Functions" PEXGeoNormTriangleStrip
.LP
This function computes the geometric normals of a triangle
strip and stores them in the specified facet data.
.LP
The geometric normal of each triangle is computed by forming
two vectors from two of its sides, and computing the cross
product of those two vectors.  The geometric normal is the
normalized cross product:
.LP
.RS
Ng = (V1 x V2) / |V1 X V2|
.RE
.LP
For the first, third, and subsequent odd-numbered triangles,
the first vector (V1) is from the first point (Pi) of the
triangle to the second point (Pi+1), and the second vector
(V2) is from the first point of the triangle to the third point
(Pi+2).  For the second, fourth, and subsequent even-numbered
triangles, the first vector is from the first point (Pi) of the
triangle to the third point (Pi+2), and the second vector is
from the first point of the triangle to the second point (Pi+1).
.LP
If the facet attributes does not contain the bit
.B PEXGANormal,
the geometric normal is not computed.  However, the function still returns
successfully.
.LP
A geometric normal is computed for all triangles where
it is possible to compute one, even if a normal cannot be
computed for some other triangles.  An error is returned
if a normal cannot be computed for one or more of the
triangles in the strip.
.SH ERRORS
None