mirror of
https://github.com/jiawanlong/Cesium-Examples.git
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140 lines
2.4 KiB
JavaScript
140 lines
2.4 KiB
JavaScript
/**
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* Parametric Surfaces Geometry
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* based on the brilliant article by @prideout https://prideout.net/blog/old/blog/index.html@p=44.html
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*/
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import {
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BufferGeometry,
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Float32BufferAttribute,
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Vector3
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} from 'three';
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class ParametricGeometry extends BufferGeometry {
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constructor( func = ( u, v, target ) => target.set( u, v, Math.cos( u ) * Math.sin( v ) ), slices = 8, stacks = 8 ) {
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super();
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this.type = 'ParametricGeometry';
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this.parameters = {
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func: func,
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slices: slices,
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stacks: stacks
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};
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// buffers
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const indices = [];
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const vertices = [];
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const normals = [];
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const uvs = [];
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const EPS = 0.00001;
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const normal = new Vector3();
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const p0 = new Vector3(), p1 = new Vector3();
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const pu = new Vector3(), pv = new Vector3();
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// generate vertices, normals and uvs
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const sliceCount = slices + 1;
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for ( let i = 0; i <= stacks; i ++ ) {
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const v = i / stacks;
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for ( let j = 0; j <= slices; j ++ ) {
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const u = j / slices;
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// vertex
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func( u, v, p0 );
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vertices.push( p0.x, p0.y, p0.z );
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// normal
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// approximate tangent vectors via finite differences
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if ( u - EPS >= 0 ) {
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func( u - EPS, v, p1 );
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pu.subVectors( p0, p1 );
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} else {
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func( u + EPS, v, p1 );
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pu.subVectors( p1, p0 );
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}
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if ( v - EPS >= 0 ) {
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func( u, v - EPS, p1 );
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pv.subVectors( p0, p1 );
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} else {
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func( u, v + EPS, p1 );
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pv.subVectors( p1, p0 );
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}
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// cross product of tangent vectors returns surface normal
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normal.crossVectors( pu, pv ).normalize();
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normals.push( normal.x, normal.y, normal.z );
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// uv
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uvs.push( u, v );
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}
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}
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// generate indices
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for ( let i = 0; i < stacks; i ++ ) {
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for ( let j = 0; j < slices; j ++ ) {
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const a = i * sliceCount + j;
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const b = i * sliceCount + j + 1;
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const c = ( i + 1 ) * sliceCount + j + 1;
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const d = ( i + 1 ) * sliceCount + j;
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// faces one and two
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indices.push( a, b, d );
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indices.push( b, c, d );
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}
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}
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// build geometry
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this.setIndex( indices );
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this.setAttribute( 'position', new Float32BufferAttribute( vertices, 3 ) );
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this.setAttribute( 'normal', new Float32BufferAttribute( normals, 3 ) );
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this.setAttribute( 'uv', new Float32BufferAttribute( uvs, 2 ) );
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}
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copy( source ) {
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super.copy( source );
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this.parameters = Object.assign( {}, source.parameters );
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return this;
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}
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}
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export { ParametricGeometry };
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