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Im Hintergrund läuft eine Planetensimulation, geschrieben in JavaScript und Three.js.
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80 lines
1.8 KiB
80 lines
1.8 KiB
import { |
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Curve, |
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Vector3, |
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Vector4 |
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} from 'three'; |
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import * as NURBSUtils from '../curves/NURBSUtils.js'; |
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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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class NURBSCurve extends Curve { |
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constructor( |
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degree, |
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knots /* array of reals */, |
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controlPoints /* array of Vector(2|3|4) */, |
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startKnot /* index in knots */, |
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endKnot /* index in knots */ |
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) { |
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super(); |
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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 ( let i = 0; i < controlPoints.length; ++ i ) { |
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// ensure Vector4 for control points |
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const point = controlPoints[ i ]; |
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this.controlPoints[ i ] = new Vector4( point.x, point.y, point.z, point.w ); |
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} |
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} |
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getPoint( t, optionalTarget = new Vector3() ) { |
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const point = optionalTarget; |
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const 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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const hpoint = 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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getTangent( t, optionalTarget = new Vector3() ) { |
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const tangent = optionalTarget; |
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const u = this.knots[ 0 ] + t * ( this.knots[ this.knots.length - 1 ] - this.knots[ 0 ] ); |
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const 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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} |
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export { NURBSCurve };
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