gecko-dev/content/smil/nsSMILKeySpline.cpp

121 lines
3.9 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is the Mozilla SMIL module.
*
* The Initial Developer of the Original Code is Brian Birtles.
* Portions created by the Initial Developer are Copyright (C) 2005
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Brian Birtles <birtles@gmail.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either of the GNU General Public License Version 2 or later (the "GPL"),
* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#include "nsSMILKeySpline.h"
#include <math.h>
#define NEWTON_ITERATIONS 4
const double nsSMILKeySpline::kSampleStepSize =
1.0 / double(kSplineTableSize - 1);
nsSMILKeySpline::nsSMILKeySpline(double aX1,
double aY1,
double aX2,
double aY2)
: mX1(aX1),
mY1(aY1),
mX2(aX2),
mY2(aY2)
{
if (mX1 != mY1 || mX2 != mY2)
CalcSampleValues();
}
double
nsSMILKeySpline::GetSplineValue(double aX) const
{
if (mX1 == mY1 && mX2 == mY2)
return aX;
return CalcBezier(GetTForX(aX), mY1, mY2);
}
void
nsSMILKeySpline::CalcSampleValues()
{
for (int i = 0; i < kSplineTableSize; ++i) {
mSampleValues[i] = CalcBezier(double(i) * kSampleStepSize, mX1, mX2);
}
}
/*static*/ double
nsSMILKeySpline::CalcBezier(double aT,
double aA1,
double aA2)
{
return A(aA1, aA2) * pow(aT,3) + B(aA1, aA2)*aT*aT + C(aA1) * aT;
}
/*static*/ double
nsSMILKeySpline::GetSlope(double aT,
double aA1,
double aA2)
{
double denom = (3.0 * A(aA1, aA2)*aT*aT + 2.0 * B(aA1, aA2) * aT + C(aA1));
return (denom == 0.0) ? 0.0 : 1.0 / denom;
}
double
nsSMILKeySpline::GetTForX(double aX) const
{
int i;
// Get an initial guess.
//
// Note: This is better than just taking x as our initial guess as cases such
// as where the control points are (1, 1), (0, 0) will take some 20 iterations
// to converge to a good accuracy. By taking an initial guess in this way we
// only need 3~4 iterations depending on the size of the table.
for (i = 0; i < kSplineTableSize - 2 && mSampleValues[i] < aX; ++i);
double currentT =
double(i) * kSampleStepSize + (aX - mSampleValues[i]) * kSampleStepSize;
// Refine with Newton-Raphson iteration
for (i = 0; i < NEWTON_ITERATIONS; ++i) {
double currentX = CalcBezier(currentT, mX1, mX2);
double currentSlope = GetSlope(currentT, mX1, mX2);
if (currentSlope == 0.0)
return currentT;
currentT -= (currentX - aX) * currentSlope;
}
return currentT;
}