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import { ZeroCurvatureEnding } from '../../constants.js';
import { Interpolant } from '../Interpolant.js';
import { WrapAroundEnding, ZeroSlopeEnding } from '../../constants.js';
/**
* Fast and simple cubic spline interpolant.
*
* It was derived from a Hermitian construction setting the first derivative
* at each sample position to the linear slope between neighboring positions
* over their parameter interval.
*
* @author tschw
*/
function CubicInterpolant( parameterPositions, sampleValues, sampleSize, resultBuffer ) {
Interpolant.call( this, parameterPositions, sampleValues, sampleSize, resultBuffer );
this._weightPrev = - 0;
this._offsetPrev = - 0;
this._weightNext = - 0;
this._offsetNext = - 0;
}
CubicInterpolant.prototype = Object.assign( Object.create( Interpolant.prototype ), {
constructor: CubicInterpolant,
DefaultSettings_: {
endingStart: ZeroCurvatureEnding,
endingEnd: ZeroCurvatureEnding
},
intervalChanged_: function ( i1, t0, t1 ) {
var pp = this.parameterPositions,
iPrev = i1 - 2,
iNext = i1 + 1,
tPrev = pp[ iPrev ],
tNext = pp[ iNext ];
if ( tPrev === undefined ) {
switch ( this.getSettings_().endingStart ) {
case ZeroSlopeEnding:
// f'(t0) = 0
iPrev = i1;
tPrev = 2 * t0 - t1;
break;
case WrapAroundEnding:
// use the other end of the curve
iPrev = pp.length - 2;
tPrev = t0 + pp[ iPrev ] - pp[ iPrev + 1 ];
break;
default: // ZeroCurvatureEnding
// f''(t0) = 0 a.k.a. Natural Spline
iPrev = i1;
tPrev = t1;
}
}
if ( tNext === undefined ) {
switch ( this.getSettings_().endingEnd ) {
case ZeroSlopeEnding:
// f'(tN) = 0
iNext = i1;
tNext = 2 * t1 - t0;
break;
case WrapAroundEnding:
// use the other end of the curve
iNext = 1;
tNext = t1 + pp[ 1 ] - pp[ 0 ];
break;
default: // ZeroCurvatureEnding
// f''(tN) = 0, a.k.a. Natural Spline
iNext = i1 - 1;
tNext = t0;
}
}
var halfDt = ( t1 - t0 ) * 0.5,
stride = this.valueSize;
this._weightPrev = halfDt / ( t0 - tPrev );
this._weightNext = halfDt / ( tNext - t1 );
this._offsetPrev = iPrev * stride;
this._offsetNext = iNext * stride;
},
interpolate_: function ( i1, t0, t, t1 ) {
var result = this.resultBuffer,
values = this.sampleValues,
stride = this.valueSize,
o1 = i1 * stride, o0 = o1 - stride,
oP = this._offsetPrev, oN = this._offsetNext,
wP = this._weightPrev, wN = this._weightNext,
p = ( t - t0 ) / ( t1 - t0 ),
pp = p * p,
ppp = pp * p;
// evaluate polynomials
var sP = - wP * ppp + 2 * wP * pp - wP * p;
var s0 = ( 1 + wP ) * ppp + ( - 1.5 - 2 * wP ) * pp + ( - 0.5 + wP ) * p + 1;
var s1 = ( - 1 - wN ) * ppp + ( 1.5 + wN ) * pp + 0.5 * p;
var sN = wN * ppp - wN * pp;
// combine data linearly
for ( var i = 0; i !== stride; ++ i ) {
result[ i ] =
sP * values[ oP + i ] +
s0 * values[ o0 + i ] +
s1 * values[ o1 + i ] +
sN * values[ oN + i ];
}
return result;
}
} );
export { CubicInterpolant };
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