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+/*
+ * (c) Copyright 1993, 1994, Silicon Graphics, Inc.
+ * ALL RIGHTS RESERVED
+ * Permission to use, copy, modify, and distribute this software for
+ * any purpose and without fee is hereby granted, provided that the above
+ * copyright notice appear in all copies and that both the copyright notice
+ * and this permission notice appear in supporting documentation, and that
+ * the name of Silicon Graphics, Inc. not be used in advertising
+ * or publicity pertaining to distribution of the software without specific,
+ * written prior permission.
+ *
+ * THE MATERIAL EMBODIED ON THIS SOFTWARE IS PROVIDED TO YOU "AS-IS"
+ * AND WITHOUT WARRANTY OF ANY KIND, EXPRESS, IMPLIED OR OTHERWISE,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY OR
+ * FITNESS FOR A PARTICULAR PURPOSE.  IN NO EVENT SHALL SILICON
+ * GRAPHICS, INC.  BE LIABLE TO YOU OR ANYONE ELSE FOR ANY DIRECT,
+ * SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY
+ * KIND, OR ANY DAMAGES WHATSOEVER, INCLUDING WITHOUT LIMITATION,
+ * LOSS OF PROFIT, LOSS OF USE, SAVINGS OR REVENUE, OR THE CLAIMS OF
+ * THIRD PARTIES, WHETHER OR NOT SILICON GRAPHICS, INC.  HAS BEEN
+ * ADVISED OF THE POSSIBILITY OF SUCH LOSS, HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE
+ * POSSESSION, USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * US Government Users Restricted Rights
+ * Use, duplication, or disclosure by the Government is subject to
+ * restrictions set forth in FAR 52.227.19(c)(2) or subparagraph
+ * (c)(1)(ii) of the Rights in Technical Data and Computer Software
+ * clause at DFARS 252.227-7013 and/or in similar or successor
+ * clauses in the FAR or the DOD or NASA FAR Supplement.
+ * Unpublished-- rights reserved under the copyright laws of the
+ * United States.  Contractor/manufacturer is Silicon Graphics,
+ * Inc., 2011 N.  Shoreline Blvd., Mountain View, CA 94039-7311.
+ *
+ * OpenGL(TM) is a trademark of Silicon Graphics, Inc.
+ */
+/*
+ * trackball.h
+ * A virtual trackball implementation
+ * Written by Gavin Bell for Silicon Graphics, November 1988.
+ */
+
+#ifndef TRACKBALL_H
+#define TRACKBALL_H
+
+
+/*
+ * Pass the x and y coordinates of the last and current positions of
+ * the mouse, scaled so they are from (-1.0 ... 1.0).
+ *
+ * The resulting rotation is returned as a quaternion rotation in the
+ * first paramater.
+ */
+void
+trackball(float q[4], float p1x, float p1y, float p2x, float p2y);
+
+/*
+ * Given two quaternions, add them together to get a third quaternion.
+ * Adding quaternions to get a compound rotation is analagous to adding
+ * translations to get a compound translation.  When incrementally
+ * adding rotations, the first argument here should be the new
+ * rotation, the second and third the total rotation (which will be
+ * over-written with the resulting new total rotation).
+ */
+void
+add_quats(const float q1[4], const float q2[4], float dest[4]);
+
+/*
+ * A useful function, builds a rotation matrix in Matrix based on
+ * given quaternion.
+ */
+void
+build_rotmatrix(float m[4][4], const float q[4]);
+
+/*
+ * This function computes a quaternion based on an axis (defined by
+ * the given vector) and an angle about which to rotate.  The angle is
+ * expressed in radians.  The result is put into the third argument.
+ */
+void
+axis_to_quat(const float a[3], float phi, float q[4]);
+
+
+#endif /* TRACKBALL_H */