BSpline.js

var BSpline = function(points,degree,copy){
    if(copy){
        this.points = []
        for(var i = 0;i<points.length;i++){
            this.points.push(points[i]);
        }
    }else{
        this.points = points;
    }
    this.degree = degree;
    this.dimension = points[0].length;
    if(degree == 2){
        this.baseFunc = this.basisDeg2;
        this.baseFuncRangeInt = 2;
    }else if(degree == 3){
        this.baseFunc = this.basisDeg3;
        this.baseFuncRangeInt = 2;
    }else if(degree == 4){
        this.baseFunc = this.basisDeg4;
        this.baseFuncRangeInt = 3;
    }else if(degree == 5){
        this.baseFunc = this.basisDeg5;
        this.baseFuncRangeInt = 3;
    } 
};

BSpline.prototype.seqAt = function(dim){
    var points = this.points;
    var margin = this.degree + 1;
    return function(n){
        if(n < margin){
            return points[0][dim];
        }else if(points.length + margin <= n){
            return points[points.length-1][dim];
        }else{
            return points[n-margin][dim];
        }
    };
};

BSpline.prototype.basisDeg2 = function(x){
    if(-0.5 <= x && x < 0.5){
        return 0.75 - x*x;
    }else if(0.5 <= x && x <= 1.5){
        return 1.125 + (-1.5 + x/2.0)*x;
    }else if(-1.5 <= x && x < -0.5){
        return 1.125 + (1.5 + x/2.0)*x;
    }else{
        return 0;
    }
};

BSpline.prototype.basisDeg3 = function(x){
    if(-1 <= x && x < 0){
        return 2.0/3.0 + (-1.0 - x/2.0)*x*x;
    }else if(1 <= x && x <= 2){
        return 4.0/3.0 + x*(-2.0 + (1.0 - x/6.0)*x);
    }else if(-2 <= x && x < -1){
        return 4.0/3.0 + x*(2.0 + (1.0 + x/6.0)*x);
    }else if(0 <= x && x < 1){
        return 2.0/3.0 + (-1.0 + x/2.0)*x*x;
    }else{
        return 0;
    }
};

BSpline.prototype.basisDeg4 = function(x){
    if(-1.5 <= x && x < -0.5){
        return 55.0/96.0 + x*(-(5.0/24.0) + x*(-(5.0/4.0) + (-(5.0/6.0) - x/6.0)*x));
    }else if(0.5 <= x && x < 1.5){
        return 55.0/96.0 + x*(5.0/24.0 + x*(-(5.0/4.0) + (5.0/6.0 - x/6.0)*x));
    }else if(1.5 <= x && x <= 2.5){
        return 625.0/384.0 + x*(-(125.0/48.0) + x*(25.0/16.0 + (-(5.0/12.0) + x/24.0)*x));
    }else if(-2.5 <= x && x <= -1.5){
        return 625.0/384.0 + x*(125.0/48.0 + x*(25.0/16.0 + (5.0/12.0 + x/24.0)*x));
    }else if(-1.5 <= x && x < 1.5){
        return 115.0/192.0 + x*x*(-(5.0/8.0) + x*x/4.0);
    }else{
        return 0;
    }
};

BSpline.prototype.basisDeg5 = function(x){
    if(-2 <= x && x < -1){
        return 17.0/40.0 + x*(-(5.0/8.0) + x*(-(7.0/4.0) + x*(-(5.0/4.0) + (-(3.0/8.0) - x/24.0)*x)));
    }else if(0 <= x && x < 1){
        return 11.0/20.0 + x*x*(-(1.0/2.0) + (1.0/4.0 - x/12.0)*x*x);
    }else if(2 <= x && x <= 3){
        return 81.0/40.0 + x*(-(27.0/8.0) + x*(9.0/4.0 + x*(-(3.0/4.0) + (1.0/8.0 - x/120.0)*x)));
    }else if(-3 <= x && x < -2){
        return 81.0/40.0 + x*(27.0/8.0 + x*(9.0/4.0 + x*(3.0/4.0 + (1.0/8.0 + x/120.0)*x)));
    }else if(1 <= x && x < 2){
        return 17.0/40.0 + x*(5.0/8.0 + x*(-(7.0/4.0) + x*(5.0/4.0 + (-(3.0/8.0) + x/24.0)*x)));
    }else if(-1 <= x && x < 0){
        return 11.0/20.0 + x*x*(-(1.0/2.0) + (1.0/4.0 + x/12.0)*x*x);
    }else{
        return 0;
    }
};

BSpline.prototype.getInterpol = function(seq,t){
    var f = this.baseFunc;
    var rangeInt = this.baseFuncRangeInt;
    var tInt = Math.floor(t);
    var result = 0;
    for(var i = tInt - rangeInt;i <= tInt + rangeInt;i++){
        result += seq(i)*f(t-i);
    }
    return result;
};

BSpline.prototype.calcAt = function(t){
    t = t*((this.degree+1)*2+this.points.length);//t must be in [0,1]
    if(this.dimension == 2){
        return [this.getInterpol(this.seqAt(0),t),this.getInterpol(this.seqAt(1),t)];
    }else if(this.dimension == 3){
        return [this.getInterpol(this.seqAt(0),t),this.getInterpol(this.seqAt(1),t),this.getInterpol(this.seqAt(2),t)];
    }else{
        var res = [];
        for(var i = 0;i<this.dimension;i++){
            res.push(this.getInterpol(this.seqAt(i),t));
        }
        return res;
    }
};