66 lines
1.7 KiB
JavaScript
66 lines
1.7 KiB
JavaScript
/**
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* @author renej
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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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/**************************************************************
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* NURBS curve
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**************************************************************/
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THREE.NURBSCurve = function ( degree, knots /* array of reals */, controlPoints /* array of Vector(2|3|4) */ ) {
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this.degree = degree;
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this.knots = knots;
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this.controlPoints = [];
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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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THREE.NURBSCurve.prototype = Object.create( THREE.Curve.prototype );
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THREE.NURBSCurve.prototype.constructor = THREE.NURBSCurve;
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THREE.NURBSCurve.prototype.getPoint = function ( t ) {
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var u = this.knots[ 0 ] + t * ( this.knots[ this.knots.length - 1 ] - this.knots[ 0 ] ); // 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 new THREE.Vector3( hpoint.x, hpoint.y, hpoint.z );
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};
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THREE.NURBSCurve.prototype.getTangent = function ( t ) {
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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 = THREE.NURBSUtils.calcNURBSDerivatives( this.degree, this.knots, this.controlPoints, u, 1 );
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var tangent = ders[ 1 ].clone();
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tangent.normalize();
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return tangent;
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};
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