69 lines
1.9 KiB
JavaScript
69 lines
1.9 KiB
JavaScript
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/**
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* NURBS curve object
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*
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* Derives from Curve, overriding getPoint and getTangent.
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*
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* Implementation is based on (x, y [, z=0 [, w=1]]) control points with w=weight.
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*
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**/
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var NURBSCurve = function ( degree, knots /* array of reals */, controlPoints /* array of Vector(2|3|4) */, startKnot /* index in knots */, endKnot /* index in knots */ ) {
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THREE.Curve.call( this );
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this.degree = degree;
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this.knots = knots;
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this.controlPoints = [];
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// Used by periodic NURBS to remove hidden spans
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this.startKnot = startKnot || 0;
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this.endKnot = endKnot || ( this.knots.length - 1 );
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for ( var i = 0; i < controlPoints.length; ++ i ) {
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// ensure Vector4 for control points
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var point = controlPoints[ i ];
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this.controlPoints[ i ] = new THREE.Vector4( point.x, point.y, point.z, point.w );
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}
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};
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NURBSCurve.prototype = Object.create( THREE.Curve.prototype );
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NURBSCurve.prototype.constructor = NURBSCurve;
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NURBSCurve.prototype.getPoint = function ( t, optionalTarget ) {
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var point = optionalTarget || new THREE.Vector3();
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var u = this.knots[ this.startKnot ] + t * ( this.knots[ this.endKnot ] - this.knots[ this.startKnot ] ); // linear mapping t->u
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// following results in (wx, wy, wz, w) homogeneous point
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var hpoint = THREE.NURBSUtils.calcBSplinePoint( this.degree, this.knots, this.controlPoints, u );
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if ( hpoint.w != 1.0 ) {
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// project to 3D space: (wx, wy, wz, w) -> (x, y, z, 1)
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hpoint.divideScalar( hpoint.w );
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}
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return point.set( hpoint.x, hpoint.y, hpoint.z );
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};
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NURBSCurve.prototype.getTangent = function ( t, optionalTarget ) {
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var tangent = optionalTarget || new Vector3();
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var u = this.knots[ 0 ] + t * ( this.knots[ this.knots.length - 1 ] - this.knots[ 0 ] );
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var ders = NURBSUtils.calcNURBSDerivatives( this.degree, this.knots, this.controlPoints, u, 1 );
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tangent.copy( ders[ 1 ] ).normalize();
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return tangent;
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};
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THREE.NURBSCurve = NURBSCurve;
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