54 lines
1.8 KiB
C++
54 lines
1.8 KiB
C++
|
// util.cxx - general-purpose utility functions.
|
||
|
|
// Copyright (C) 2002 Curtis L. Olson - curt@me.umn.edu
|
||
|
|
//
|
||
|
|
// This program is free software; you can redistribute it and/or
|
||
|
|
// modify it under the terms of the GNU General Public License as
|
||
|
|
// published by the Free Software Foundation; either version 2 of the
|
||
|
|
// License, or (at your option) any later version.
|
||
|
|
//
|
||
|
|
// This program is distributed in the hope that it will be useful, but
|
||
|
|
// WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
|
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||
|
|
// General Public License for more details.
|
||
|
|
//
|
||
|
|
// You should have received a copy of the GNU General Public License
|
||
|
|
// along with this program; if not, write to the Free Software
|
||
|
|
// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
|
||
|
|
//
|
||
|
|
// $Id$
|
||
|
|
|
||
|
|
|
||
|
|
#include <math.h>
|
||
|
|
#include "util.hxx"
|
||
|
|
|
||
|
|
|
||
|
|
// Originally written by Alex Perry.
|
||
|
|
double
|
||
|
|
fgGetLowPass (double current, double target, double timeratio)
|
||
|
|
{
|
||
|
|
if ( timeratio < 0.0 ) {
|
||
|
|
if ( timeratio < -1.0 ) {
|
||
|
|
// time went backwards; kill the filter
|
||
|
|
current = target;
|
||
|
|
} else {
|
||
|
|
// ignore mildly negative time
|
||
|
|
}
|
||
|
|
} else if ( timeratio < 0.2 ) {
|
||
|
|
// Normal mode of operation; fast
|
||
|
|
// approximation to exp(-timeratio)
|
||
|
|
current = current * (1.0 - timeratio) + target * timeratio;
|
||
|
|
} else if ( timeratio > 5.0 ) {
|
||
|
|
// Huge time step; assume filter has settled
|
||
|
|
current = target;
|
||
|
|
} else {
|
||
|
|
// Moderate time step; non linear response
|
||
|
|
double keep = exp(-timeratio);
|
||
|
|
current = current * keep + target * (1.0 - keep);
|
||
|
|
}
|
||
|
|
|
||
|
|
return current;
|
||
|
|
}
|
||
|
|
|
||
|
|
// end of util.cxx
|
||
|
|
|