1 /*
2 * The 3D Studio File Format Library
3 * Copyright (C) 1996-2007 by Jan Eric Kyprianidis <www.kyprianidis.com>
4 * All rights reserved.
5 *
6 * This program is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU Lesser General Public License as published by
8 * the Free Software Foundation; either version 2.1 of the License, or (at
9 * your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
13 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
14 * License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public License
17 * along with this program; if not, write to the Free Software Foundation,
18 * Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
19 *
20 * $Id: ease.c,v 1.6 2007/06/15 09:33:19 jeh Exp $
21 */
22 #include <lib3ds/ease.h>
23
24
25 /*!
26 * \defgroup ease Ease
27 */
28
29
30 /*!
31 * \ingroup ease
32 */
33 Lib3dsFloat
lib3ds_ease(Lib3dsFloat fp,Lib3dsFloat fc,Lib3dsFloat fn,Lib3dsFloat ease_from,Lib3dsFloat ease_to)34 lib3ds_ease(Lib3dsFloat fp, Lib3dsFloat fc, Lib3dsFloat fn,
35 Lib3dsFloat ease_from, Lib3dsFloat ease_to)
36 {
37 Lib3dsDouble s,step;
38 Lib3dsDouble tofrom;
39 Lib3dsDouble a;
40
41 s=step=(Lib3dsFloat)(fc-fp)/(fn-fp);
42 tofrom=ease_to+ease_from;
43 if (tofrom!=0.0) {
44 if (tofrom>1.0) {
45 ease_to=(Lib3dsFloat)(ease_to/tofrom);
46 ease_from=(Lib3dsFloat)(ease_from/tofrom);
47 }
48 a=1.0/(2.0-(ease_to+ease_from));
49
50 if (step<ease_from) s=a/ease_from*step*step;
51 else {
52 if ((1.0-ease_to)<=step) {
53 step=1.0-step;
54 s=1.0-a/ease_to*step*step;
55 }
56 else {
57 s=((2.0*step)-ease_from)*a;
58 }
59 }
60 }
61 return((Lib3dsFloat)s);
62 }
63