http://ftp.ksu.edu.tw/FTP/FreeBSD/distfiles/xscreensaver-4.20.tar.gz

[xscreensaver] / hacks / glx / normals.c

diff --git a/hacks/glx/normals.c b/hacks/glx/normals.c
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+/* 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.
+ */
+
+#include "config.h"
+#include <GL/gl.h>
+#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);
+}