/* normals, Copyright (c) 2002-2004 Jamie Zawinski <jwz@jwz.org>
*
* Permission to use, copy, modify, distribute, and sell this software and its
* documentation for any purpose is hereby granted without fee, provided that
* the above copyright notice appear in all copies and that both that
* copyright notice and this permission notice appear in supporting
* documentation. No representations are made about the suitability of this
* software for any purpose. It is provided "as is" without express or
* implied warranty.
*
* Compute normal vectors for arbitrary triangles.
*/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#include "normals.h"
/* Calculate the unit normal at p given two other points p1,p2 on the
surface. The normal points in the direction of p1 crossproduct p2
*/
XYZ
calc_normal (XYZ p, XYZ p1, XYZ p2)
{
XYZ n, pa, pb;
pa.x = p1.x - p.x;
pa.y = p1.y - p.y;
pa.z = p1.z - p.z;
pb.x = p2.x - p.x;
pb.y = p2.y - p.y;
pb.z = p2.z - p.z;
n.x = pa.y * pb.z - pa.z * pb.y;
n.y = pa.z * pb.x - pa.x * pb.z;
n.z = pa.x * pb.y - pa.y * pb.x;
return (n);
}
/* Call glNormal3f() with a normal of the indicated triangle.
*/
void
do_normal(GLfloat x1, GLfloat y1, GLfloat z1,
GLfloat x2, GLfloat y2, GLfloat z2,
GLfloat x3, GLfloat y3, GLfloat z3)
{
XYZ p1, p2, p3, p;
p1.x = x1; p1.y = y1; p1.z = z1;
p2.x = x2; p2.y = y2; p2.z = z2;
p3.x = x3; p3.y = y3; p3.z = z3;
p = calc_normal (p1, p2, p3);
glNormal3f (p.x, p.y, p.z);
}
