Question

按照这里的例子：

http://learningthreejs.com/blog/2011/12/10/constructive-solid-geometry-with-csg-js/

使用带有https://github.com/chandlerprall/ThreeCSG的Three.js，我试图在模型的节点上进行3D布尔运算。例如，如果我有一个带窗口的墙，我想在其上做invert()以获得窗口。

我有一个返回节点多边形顶点的函数，这里是一个没有洞https://pastebin.com/8dhYzPwE的对象顶点的例子。

我正在使用ThreeCSG：

    const geometryThree = new THREE.Geometry();

    geometryThree.vertices.push(
        ...vertices
    );

    const geometryCsg = new ThreeBSP(geometryThree);

但这就是我在geometryCsg中所得到的：

"{
    "matrix": {
        "elements": {
            "0": 1,
            "1": 0,
            "2": 0,
            "3": 0,
            "4": 0,
            "5": 1,
            "6": 0,
            "7": 0,
            "8": 0,
            "9": 0,
            "10": 1,
            "11": 0,
            "12": 0,
            "13": 0,
            "14": 0,
            "15": 1
        }
    },
    "tree": {
        "polygons": []
    }
}"

我认为这是因为the geometry.faces.length is 0。

如何使顶点数组成为正确的Three.Geometry，使得面不会为空？ Geometry.elementsNeedsUpdate不起作用......

是否有一个示例使用形状的多边形作为Vector3的数组并将其转换为csg？

Answer 1

我刚刚使用THREE csg进行了演示：Viewer网格有一个索引的顶点数组，因此您无法直接创建BSP。此外，我的代码使用Web工作程序来处理网格以保持UI响应大型模型，因此我首先需要将网格数据发送给工作者并在工作方重建一个简单的THREE.Mesh，代码看起来如下所示：

// Sends component geometry to the web worker  
postComponent (dbId) {

  const geometry = this.getComponentGeometry(dbId)

  const msg = {
    boundingBox: this.getComponentBoundingBox(dbId),
    matrixWorld: geometry.matrixWorld,
    nbMeshes: geometry.meshes.length,
    msgId: 'MSG_ID_COMPONENT',
    dbId
  }

  geometry.meshes.forEach((mesh, idx) => {

    msg['positions' + idx] = mesh.positions
    msg['indices' + idx] = mesh.indices
    msg['stride' + idx] = mesh.stride
  })

  this.worker.postMessage(msg)
}

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

  const fragIds = Toolkit.getLeafFragIds(
    this.viewer.model, dbId)

  let matrixWorld = null

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

    const renderProxy = this.viewer.impl.getRenderProxy(
      this.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
  }
}


// On the worker side reconstruct THREE.Mesh
// from received data and create ThreeBSP
function buildComponentMesh (data) {

  const vertexArray = []

  for (let idx=0; idx < data.nbMeshes; ++idx) {

    const meshData = {
      positions: data['positions' + idx],
      indices: data['indices' + idx],
      stride: data['stride' + idx]
    }

    getMeshGeometry (meshData, vertexArray)
  }

  const geometry = new THREE.Geometry()

  for (var 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(data.matrixWorld)

  const mesh = new THREE.Mesh(geometry)

  mesh.applyMatrix(matrixWorld)

  mesh.boundingBox = data.boundingBox

  mesh.bsp = new ThreeBSP(mesh)

  mesh.dbId = data.dbId

  return mesh
}

function getMeshGeometry (data, vertexArray) {

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

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

    var start = offsets[oi].start
    var count = offsets[oi].count
    var index = offsets[oi].index

    for (var 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)
    }
  }
}

我的示例的完整代码在那里：Wall Analyzer和现场演示there。

使用三个CSG进行3D布尔运算

1 个答案: