/** 
 * @file llcriticaldamp.cpp
 * @brief Implementation of the critical damping functionality.
 *
 * $LicenseInfo:firstyear=2002&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 * 
 * This library 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
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 * 
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#include "linden_common.h"

#include "llcriticaldamp.h"
#include <algorithm>

//-----------------------------------------------------------------------------
// static members
//-----------------------------------------------------------------------------
LLFrameTimer LLSmoothInterpolation::sInternalTimer;
std::vector<LLSmoothInterpolation::Interpolant> LLSmoothInterpolation::sInterpolants;
F32 LLSmoothInterpolation::sTimeDelta;

// helper functors
struct LLSmoothInterpolation::CompareTimeConstants
{
	bool operator()(const F32& a, const LLSmoothInterpolation::Interpolant& b) const
	{
		return a < b.mTimeScale;
	}

	bool operator()(const LLSmoothInterpolation::Interpolant& a, const F32& b) const
	{
		return a.mTimeScale < b; // bottom of a is higher than bottom of b
	}

	bool operator()(const LLSmoothInterpolation::Interpolant& a, const LLSmoothInterpolation::Interpolant& b) const
	{
		return a.mTimeScale < b.mTimeScale; // bottom of a is higher than bottom of b
	}
};

//-----------------------------------------------------------------------------
// LLSmoothInterpolation()
//-----------------------------------------------------------------------------
LLSmoothInterpolation::LLSmoothInterpolation()
{
	sTimeDelta = 0.f;
}

// static
//-----------------------------------------------------------------------------
// updateInterpolants()
//-----------------------------------------------------------------------------
void LLSmoothInterpolation::updateInterpolants()
{
	sTimeDelta = sInternalTimer.getElapsedTimeAndResetF32();

	for (S32 i = 0; i < sInterpolants.size(); i++)
	{
		Interpolant& interp = sInterpolants[i];
		interp.mInterpolant = calcInterpolant(interp.mTimeScale);
	}
} 

//-----------------------------------------------------------------------------
// getInterpolant()
//-----------------------------------------------------------------------------
F32 LLSmoothInterpolation::getInterpolant(LLUnitImplicit<F32, LLUnits::Seconds> time_constant, bool use_cache)
{
	if (time_constant == 0.f)
	{
		return 1.f;
	}

	if (use_cache)
	{
		interpolant_vec_t::iterator find_it = std::lower_bound(sInterpolants.begin(), sInterpolants.end(), time_constant.value(), CompareTimeConstants());
		if (find_it != sInterpolants.end() && find_it->mTimeScale == time_constant) 
		{
			return find_it->mInterpolant;
		}
		else
		{
			Interpolant interp;
			interp.mTimeScale = time_constant.value();
			interp.mInterpolant = calcInterpolant(time_constant.value());
			sInterpolants.insert(find_it, interp);
			return interp.mInterpolant;
		}
	}
	else
	{
		return calcInterpolant(time_constant.value());

	}
}

//-----------------------------------------------------------------------------
// calcInterpolant()
//-----------------------------------------------------------------------------
F32 LLSmoothInterpolation::calcInterpolant(F32 time_constant)
{
	return llclamp(1.f - powf(2.f, -sTimeDelta / time_constant), 0.f, 1.f);
}