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Globally-useful functions, starting with Alex Perry's low-pass

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function from steam.cxx.
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david 2002-09-27 22:01:33 +00:00
parent b81139dab3
commit 84d2627236
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src/Main/util.cxx Normal file
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// 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

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// util.hxx - 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.
//
// $Id$
#ifndef __UTIL_HXX
#define __UTIL_HXX 1
#ifndef __cplusplus
# error This library requires C++
#endif
/**
* Move a value towards a target.
*
* This function was originally written by Alex Perry.
*
* @param current The current value.
* @param target The target value.
* @param timeratio The percentage of smoothing time that has passed
* (elapsed time/smoothing time)
* @return The new value.
*/
extern double fgGetLowPass (double current, double target, double timeratio);
#endif // __UTIL_HXX