从 Forge Viewer Mesh 信息创建 THREE.Mesh

如下示例如何从Forge Viewer 的 Mesh 信息创建 THREE.Mesh，函数进入点是 buildComponentMesh：

function getLeafFragIds( model, leafId ) {
  const instanceTree = model.getData().instanceTree;
  const fragIds = [];

  instanceTree.enumNodeFragments( leafId, function( fragId ) {
    fragIds.push( fragId );
  });

  return fragIds;
}

function getModifiedWorldBoundingBox( fragIds, fragList ) {

  const fragbBox = new THREE.Box3();
  const nodebBox = new THREE.Box3();

  fragIds.forEach( function( fragId ) {
    fragList.getWorldBounds( fragId, fragbBox );

    nodebBox.union( fragbBox );
  });

  return nodebBox;
}

function getComponentBoundingBox( model, dbId) {
  const fragIds = getLeafFragIds( model, dbId );
  const fragList = model.getFragmentList();

  return getModifiedWorldBoundingBox( fragIds, fragList );
}

function getMeshGeometry( data, vertexArray ) {

  const offsets = [{
    count: data.indices.length,
    index: 0,
    start: 0
  }];

  for( let oi = 0, ol = offsets.length; oi < ol; ++oi ) {

    let start = offsets[oi].start;
    let count = offsets[oi].count;
    let index = offsets[oi].index;

    for( let i = start, il = start + count; i < il; i += 3) {

      const a = index + data.indices[i];
      const b = index + data.indices[i + 1];
      const c = index + data.indices[i + 2];

      const vA = new THREE.Vector3();
      const vB = new THREE.Vector3();
      const vC = new THREE.Vector3();

      vA.fromArray( data.positions, a * data.stride );
      vB.fromArray( data.positions, b * data.stride );
      vC.fromArray( data.positions, c * data.stride );

      vertexArray.push( vA );
      vertexArray.push( vB );
      vertexArray.push( vC );
    }
  }
}


// Build THREE.Mesh
function buildComponentMesh( viewer, dbId ) {

  const geometry = getComponentGeometry( viewer, dbId );

  const boundingBox =getComponentBoundingBox( viewer.model, dbId );
  const matrixWorld = geometry.matrixWorld;
  const nbMeshes = geometry.meshes.length;

  const vertexArray = [];

  for( let idx=0; idx < nbMeshes; ++idx ) {
    const mesh = geometry.meshes[idx];

    const meshData = {
      positions: mesh.positions,
      indices: mesh.indices,
      stride: mesh.stride
    };

    getMeshGeometry( meshData, vertexArray );
  }

  const geometry = new THREE.Geometry();

  for( let i = 0; i < vertexArray.length; i += 3 ) {

    geometry.vertices.push( vertexArray[i] );
    geometry.vertices.push( vertexArray[i + 1] );
    geometry.vertices.push( vertexArray[i + 2] );

    const face = new THREE.Face3( i, i + 1, i + 2 );

    geometry.faces.push( face );
  }

  const matrixWorld = new THREE.Matrix4();

  matrixWorld.fromArray( matrixWorld );

  const mesh = new THREE.Mesh( geometry );

  mesh.applyMatrix( matrixWorld );

  mesh.boundingBox = boundingBox;

  mesh.dbId = dbId;

  return mesh;
}

// get geometry for all fragments in a component
function getComponentGeometry( viewer, dbId ) {

  const fragIds = getLeafFragIds( viewer.model, dbId );

  let matrixWorld = null;

  const meshes = fragIds.map( function( fragId ) {

    const renderProxy = viewer.impl.getRenderProxy( viewer.model, fragId );

    const geometry = renderProxy.geometry;
    const attributes = geometry.attributes;
    const positions = geometry.vb ? geometry.vb : attributes.position.array;

    const indices = attributes.index.array || geometry.ib;
    const stride = geometry.vb ? geometry.vbstride : 3;
    const offsets = geometry.offsets;

    matrixWorld = matrixWorld || renderProxy.matrixWorld.elements;

    return {
      positions,
      indices,
      offsets,
      stride
    };
  });

  return {
    matrixWorld,
    meshes
  };
}



// 在这边调用 buildComponentMesh 函数取得 THREE.Mesh
var threeMesh = buildComponentMesh( viewer, dbId );
console.log( threeMesh );

参考：Autodesk forge-rcdb.nodejs 工程