animated/lib/bezier.js

Declarative Animations Library for React and React Native

var NEWTON_ITERATIONS=4;
var NEWTON_MIN_SLOPE=0.001;
var SUBDIVISION_PRECISION=0.0000001;
var SUBDIVISION_MAX_ITERATIONS=10;

var kSplineTableSize=11;
var kSampleStepSize=1.0/(kSplineTableSize-1.0);

var float32ArraySupported=typeof Float32Array==='function';

function A(aA1,aA2){return 1.0-3.0*aA2+3.0*aA1;}
function B(aA1,aA2){return 3.0*aA2-6.0*aA1;}
function C(aA1){return 3.0*aA1;}


function calcBezier(aT,aA1,aA2){return((A(aA1,aA2)*aT+B(aA1,aA2))*aT+C(aA1))*aT;}


function getSlope(aT,aA1,aA2){return 3.0*A(aA1,aA2)*aT*aT+2.0*B(aA1,aA2)*aT+C(aA1);}

function binarySubdivide(aX,aA,aB,mX1,mX2){
var currentX,currentT,i=0;
do{
currentT=aA+(aB-aA)/2.0;
currentX=calcBezier(currentT,mX1,mX2)-aX;
if(currentX>0.0){
aB=currentT;
}else{
aA=currentT;
}
}while(Math.abs(currentX)>SUBDIVISION_PRECISION&&++i<SUBDIVISION_MAX_ITERATIONS);
return currentT;
}

function newtonRaphsonIterate(aX,aGuessT,mX1,mX2){
for(var i=0;i<NEWTON_ITERATIONS;++i){
var currentSlope=getSlope(aGuessT,mX1,mX2);
if(currentSlope===0.0){
return aGuessT;
}
var currentX=calcBezier(aGuessT,mX1,mX2)-aX;
aGuessT-=currentX/currentSlope;
}
return aGuessT;
}

module.exports=function bezier(mX1,mY1,mX2,mY2){
if(!(0<=mX1&&mX1<=1&&0<=mX2&&mX2<=1)){
throw new Error('bezier x values must be in [0, 1] range');
}


var sampleValues=float32ArraySupported?new Float32Array(kSplineTableSize):new Array(kSplineTableSize);
if(mX1!==mY1||mX2!==mY2){
for(var i=0;i<kSplineTableSize;++i){
sampleValues[i]=calcBezier(i*kSampleStepSize,mX1,mX2);
}
}

function getTForX(aX){
var intervalStart=0.0;
var currentSample=1;
var lastSample=kSplineTableSize-1;

for(;currentSample!==lastSample&&sampleValues[currentSample]<=aX;++currentSample){
intervalStart+=kSampleStepSize;
}
--currentSample;


var dist=(aX-sampleValues[currentSample])/(sampleValues[currentSample+1]-sampleValues[currentSample]);
var guessForT=intervalStart+dist*kSampleStepSize;

var initialSlope=getSlope(guessForT,mX1,mX2);
if(initialSlope>=NEWTON_MIN_SLOPE){
return newtonRaphsonIterate(aX,guessForT,mX1,mX2);
}else if(initialSlope===0.0){
return guessForT;
}else{
return binarySubdivide(aX,intervalStart,intervalStart+kSampleStepSize,mX1,mX2);
}
}

return function BezierEasing(x){
if(mX1===mY1&&mX2===mY2){
return x;
}

if(x===0){
return 0;
}
if(x===1){
return 1;
}
return calcBezier(getTForX(x),mY1,mY2);
};
};