( function () {
/**
* NURBS utils
*
* See NURBSCurve and NURBSSurface.
**/
/**************************************************************
* NURBS Utils
**************************************************************/
/*
Finds knot vector span.
p : degree
u : parametric value
U : knot vector
returns the span
*/
function findSpan( p, u, U ) {
const n = U.length - p - 1;
if ( u >= U[ n ] ) {
return n - 1;
}
if ( u <= U[ p ] ) {
return p;
}
let low = p;
let high = n;
let mid = Math.floor( ( low + high ) / 2 );
while ( u < U[ mid ] || u >= U[ mid + 1 ] ) {
if ( u < U[ mid ] ) {
high = mid;
} else {
low = mid;
}
mid = Math.floor( ( low + high ) / 2 );
}
return mid;
}
/*
Calculate basis functions. See The NURBS Book, page 70, algorithm A2.2
span : span in which u lies
u : parametric point
p : degree
U : knot vector
returns array[p+1] with basis functions values.
*/
function calcBasisFunctions( span, u, p, U ) {
const N = [];
const left = [];
const right = [];
N[ 0 ] = 1.0;
for ( let j = 1; j <= p; ++ j ) {
left[ j ] = u - U[ span + 1 - j ];
right[ j ] = U[ span + j ] - u;
let saved = 0.0;
for ( let r = 0; r < j; ++ r ) {
const rv = right[ r + 1 ];
const lv = left[ j - r ];
const temp = N[ r ] / ( rv + lv );
N[ r ] = saved + rv * temp;
saved = lv * temp;
}
N[ j ] = saved;
}
return N;
}
/*
Calculate B-Spline curve points. See The NURBS Book, page 82, algorithm A3.1.
p : degree of B-Spline
U : knot vector
P : control points (x, y, z, w)
u : parametric point
returns point for given u
*/
function calcBSplinePoint( p, U, P, u ) {
const span = findSpan( p, u, U );
const N = calcBasisFunctions( span, u, p, U );
const C = new THREE.Vector4( 0, 0, 0, 0 );
for ( let j = 0; j <= p; ++ j ) {
const point = P[ span - p + j ];
const Nj = N[ j ];
const wNj = point.w * Nj;
C.x += point.x * wNj;
C.y += point.y * wNj;
C.z += point.z * wNj;
C.w += point.w * Nj;
}
return C;
}
/*
Calculate basis functions derivatives. See The NURBS Book, page 72, algorithm A2.3.
span : span in which u lies
u : parametric point
p : degree
n : number of derivatives to calculate
U : knot vector
returns array[n+1][p+1] with basis functions derivatives
*/
function calcBasisFunctionDerivatives( span, u, p, n, U ) {
const zeroArr = [];
for ( let i = 0; i <= p; ++ i ) zeroArr[ i ] = 0.0;
const ders = [];
for ( let i = 0; i <= n; ++ i ) ders[ i ] = zeroArr.slice( 0 );
const ndu = [];
for ( let i = 0; i <= p; ++ i ) ndu[ i ] = zeroArr.slice( 0 );
ndu[ 0 ][ 0 ] = 1.0;
const left = zeroArr.slice( 0 );
const right = zeroArr.slice( 0 );
for ( let j = 1; j <= p; ++ j ) {
left[ j ] = u - U[ span + 1 - j ];
right[ j ] = U[ span + j ] - u;
let saved = 0.0;
for ( let r = 0; r < j; ++ r ) {
const rv = right[ r + 1 ];
const lv = left[ j - r ];
ndu[ j ][ r ] = rv + lv;
const temp = ndu[ r ][ j - 1 ] / ndu[ j ][ r ];
ndu[ r ][ j ] = saved + rv * temp;
saved = lv * temp;
}
ndu[ j ][ j ] = saved;
}
for ( let j = 0; j <= p; ++ j ) {
ders[ 0 ][ j ] = ndu[ j ][ p ];
}
for ( let r = 0; r <= p; ++ r ) {
let s1 = 0;
let s2 = 1;
const a = [];
for ( let i = 0; i <= p; ++ i ) {
a[ i ] = zeroArr.slice( 0 );
}
a[ 0 ][ 0 ] = 1.0;
for ( let k = 1; k <= n; ++ k ) {
let d = 0.0;
const rk = r - k;
const pk = p - k;
if ( r >= k ) {
a[ s2 ][ 0 ] = a[ s1 ][ 0 ] / ndu[ pk + 1 ][ rk ];
d = a[ s2 ][ 0 ] * ndu[ rk ][ pk ];
}
const j1 = rk >= - 1 ? 1 : - rk;
const j2 = r - 1 <= pk ? k - 1 : p - r;
for ( let j = j1; j <= j2; ++ j ) {
a[ s2 ][ j ] = ( a[ s1 ][ j ] - a[ s1 ][ j - 1 ] ) / ndu[ pk + 1 ][ rk + j ];
d += a[ s2 ][ j ] * ndu[ rk + j ][ pk ];
}
if ( r <= pk ) {
a[ s2 ][ k ] = - a[ s1 ][ k - 1 ] / ndu[ pk + 1 ][ r ];
d += a[ s2 ][ k ] * ndu[ r ][ pk ];
}
ders[ k ][ r ] = d;
const j = s1;
s1 = s2;
s2 = j;
}
}
let r = p;
for ( let k = 1; k <= n; ++ k ) {
for ( let j = 0; j <= p; ++ j ) {
ders[ k ][ j ] *= r;
}
r *= p - k;
}
return ders;
}
/*
Calculate derivatives of a B-Spline. See The NURBS Book, page 93, algorithm A3.2.
p : degree
U : knot vector
P : control points
u : Parametric points
nd : number of derivatives
returns array[d+1] with derivatives
*/
function calcBSplineDerivatives( p, U, P, u, nd ) {
const du = nd < p ? nd : p;
const CK = [];
const span = findSpan( p, u, U );
const nders = calcBasisFunctionDerivatives( span, u, p, du, U );
const Pw = [];
for ( let i = 0; i < P.length; ++ i ) {
const point = P[ i ].clone();
const w = point.w;
point.x *= w;
point.y *= w;
point.z *= w;
Pw[ i ] = point;
}
for ( let k = 0; k <= du; ++ k ) {
const point = Pw[ span - p ].clone().multiplyScalar( nders[ k ][ 0 ] );
for ( let j = 1; j <= p; ++ j ) {
point.add( Pw[ span - p + j ].clone().multiplyScalar( nders[ k ][ j ] ) );
}
CK[ k ] = point;
}
for ( let k = du + 1; k <= nd + 1; ++ k ) {
CK[ k ] = new THREE.Vector4( 0, 0, 0 );
}
return CK;
}
/*
Calculate "K over I"
returns k!/(i!(k-i)!)
*/
function calcKoverI( k, i ) {
let nom = 1;
for ( let j = 2; j <= k; ++ j ) {
nom *= j;
}
let denom = 1;
for ( let j = 2; j <= i; ++ j ) {
denom *= j;
}
for ( let j = 2; j <= k - i; ++ j ) {
denom *= j;
}
return nom / denom;
}
/*
Calculate derivatives (0-nd) of rational curve. See The NURBS Book, page 127, algorithm A4.2.
Pders : result of function calcBSplineDerivatives
returns array with derivatives for rational curve.
*/
function calcRationalCurveDerivatives( Pders ) {
const nd = Pders.length;
const Aders = [];
const wders = [];
for ( let i = 0; i < nd; ++ i ) {
const point = Pders[ i ];
Aders[ i ] = new THREE.Vector3( point.x, point.y, point.z );
wders[ i ] = point.w;
}
const CK = [];
for ( let k = 0; k < nd; ++ k ) {
const v = Aders[ k ].clone();
for ( let i = 1; i <= k; ++ i ) {
v.sub( CK[ k - i ].clone().multiplyScalar( calcKoverI( k, i ) * wders[ i ] ) );
}
CK[ k ] = v.divideScalar( wders[ 0 ] );
}
return CK;
}
/*
Calculate NURBS curve derivatives. See The NURBS Book, page 127, algorithm A4.2.
p : degree
U : knot vector
P : control points in homogeneous space
u : parametric points
nd : number of derivatives
returns array with derivatives.
*/
function calcNURBSDerivatives( p, U, P, u, nd ) {
const Pders = calcBSplineDerivatives( p, U, P, u, nd );
return calcRationalCurveDerivatives( Pders );
}
/*
Calculate rational B-Spline surface point. See The NURBS Book, page 134, algorithm A4.3.
p1, p2 : degrees of B-Spline surface
U1, U2 : knot vectors
P : control points (x, y, z, w)
u, v : parametric values
returns point for given (u, v)
*/
function calcSurfacePoint( p, q, U, V, P, u, v, target ) {
const uspan = findSpan( p, u, U );
const vspan = findSpan( q, v, V );
const Nu = calcBasisFunctions( uspan, u, p, U );
const Nv = calcBasisFunctions( vspan, v, q, V );
const temp = [];
for ( let l = 0; l <= q; ++ l ) {
temp[ l ] = new THREE.Vector4( 0, 0, 0, 0 );
for ( let k = 0; k <= p; ++ k ) {
const point = P[ uspan - p + k ][ vspan - q + l ].clone();
const w = point.w;
point.x *= w;
point.y *= w;
point.z *= w;
temp[ l ].add( point.multiplyScalar( Nu[ k ] ) );
}
}
const Sw = new THREE.Vector4( 0, 0, 0, 0 );
for ( let l = 0; l <= q; ++ l ) {
Sw.add( temp[ l ].multiplyScalar( Nv[ l ] ) );
}
Sw.divideScalar( Sw.w );
target.set( Sw.x, Sw.y, Sw.z );
}
THREE.NURBSUtils = {};
THREE.NURBSUtils.calcBSplineDerivatives = calcBSplineDerivatives;
THREE.NURBSUtils.calcBSplinePoint = calcBSplinePoint;
THREE.NURBSUtils.calcBasisFunctionDerivatives = calcBasisFunctionDerivatives;
THREE.NURBSUtils.calcBasisFunctions = calcBasisFunctions;
THREE.NURBSUtils.calcKoverI = calcKoverI;
THREE.NURBSUtils.calcNURBSDerivatives = calcNURBSDerivatives;
THREE.NURBSUtils.calcRationalCurveDerivatives = calcRationalCurveDerivatives;
THREE.NURBSUtils.calcSurfacePoint = calcSurfacePoint;
THREE.NURBSUtils.findSpan = findSpan;
} )();
