bytev-charts-beta/lib/plugin/three.js/examples/js/renderers/Projector.js

基于echarts和JavaScript及ES6封装的一个可以直接调用的图表组件库，内置主题设计，简单快捷，且支持用户自定义配置； npm 安装方式: npm install bytev-charts 若启动提示还需额外install插件,则运行 npm install @babel/runtime-corejs2 即可;

import _Array$isArray from "@babel/runtime-corejs2/core-js/array/is-array";
import "core-js/modules/es.array.sort.js";
console.warn("THREE.Projector: As part of the transition to ES6 Modules, the files in 'examples/js' were deprecated in May 2020 (r117) and will be deleted in December 2020 (r124). You can find more information about developing using ES6 Modules in https://threejs.org/docs/#manual/en/introduction/Installation.");

THREE.RenderableObject = function () {
  this.id = 0;
  this.object = null;
  this.z = 0;
  this.renderOrder = 0;
}; //


THREE.RenderableFace = function () {
  this.id = 0;
  this.v1 = new THREE.RenderableVertex();
  this.v2 = new THREE.RenderableVertex();
  this.v3 = new THREE.RenderableVertex();
  this.normalModel = new THREE.Vector3();
  this.vertexNormalsModel = [new THREE.Vector3(), new THREE.Vector3(), new THREE.Vector3()];
  this.vertexNormalsLength = 0;
  this.color = new THREE.Color();
  this.material = null;
  this.uvs = [new THREE.Vector2(), new THREE.Vector2(), new THREE.Vector2()];
  this.z = 0;
  this.renderOrder = 0;
}; //


THREE.RenderableVertex = function () {
  this.position = new THREE.Vector3();
  this.positionWorld = new THREE.Vector3();
  this.positionScreen = new THREE.Vector4();
  this.visible = true;
};

THREE.RenderableVertex.prototype.copy = function (vertex) {
  this.positionWorld.copy(vertex.positionWorld);
  this.positionScreen.copy(vertex.positionScreen);
}; //


THREE.RenderableLine = function () {
  this.id = 0;
  this.v1 = new THREE.RenderableVertex();
  this.v2 = new THREE.RenderableVertex();
  this.vertexColors = [new THREE.Color(), new THREE.Color()];
  this.material = null;
  this.z = 0;
  this.renderOrder = 0;
}; //


THREE.RenderableSprite = function () {
  this.id = 0;
  this.object = null;
  this.x = 0;
  this.y = 0;
  this.z = 0;
  this.rotation = 0;
  this.scale = new THREE.Vector2();
  this.material = null;
  this.renderOrder = 0;
}; //


THREE.Projector = function () {
  var _object,
      _objectCount,
      _objectPool = [],
      _objectPoolLength = 0,
      _vertex,
      _vertexCount,
      _vertexPool = [],
      _vertexPoolLength = 0,
      _face,
      _faceCount,
      _facePool = [],
      _facePoolLength = 0,
      _line,
      _lineCount,
      _linePool = [],
      _linePoolLength = 0,
      _sprite,
      _spriteCount,
      _spritePool = [],
      _spritePoolLength = 0,
      _renderData = {
    objects: [],
    lights: [],
    elements: []
  },
      _vector3 = new THREE.Vector3(),
      _vector4 = new THREE.Vector4(),
      _clipBox = new THREE.Box3(new THREE.Vector3(-1, -1, -1), new THREE.Vector3(1, 1, 1)),
      _boundingBox = new THREE.Box3(),
      _points3 = new Array(3),
      _viewMatrix = new THREE.Matrix4(),
      _viewProjectionMatrix = new THREE.Matrix4(),
      _modelMatrix,
      _modelViewProjectionMatrix = new THREE.Matrix4(),
      _normalMatrix = new THREE.Matrix3(),
      _frustum = new THREE.Frustum(),
      _clippedVertex1PositionScreen = new THREE.Vector4(),
      _clippedVertex2PositionScreen = new THREE.Vector4(); //


  this.projectVector = function (vector, camera) {
    console.warn('THREE.Projector: .projectVector() is now vector.project().');
    vector.project(camera);
  };

  this.unprojectVector = function (vector, camera) {
    console.warn('THREE.Projector: .unprojectVector() is now vector.unproject().');
    vector.unproject(camera);
  };

  this.pickingRay = function () {
    console.error('THREE.Projector: .pickingRay() is now raycaster.setFromCamera().');
  }; //


  var RenderList = function RenderList() {
    var normals = [];
    var colors = [];
    var uvs = [];
    var object = null;
    var normalMatrix = new THREE.Matrix3();

    function setObject(value) {
      object = value;
      normalMatrix.getNormalMatrix(object.matrixWorld);
      normals.length = 0;
      colors.length = 0;
      uvs.length = 0;
    }

    function projectVertex(vertex) {
      var position = vertex.position;
      var positionWorld = vertex.positionWorld;
      var positionScreen = vertex.positionScreen;
      positionWorld.copy(position).applyMatrix4(_modelMatrix);
      positionScreen.copy(positionWorld).applyMatrix4(_viewProjectionMatrix);
      var invW = 1 / positionScreen.w;
      positionScreen.x *= invW;
      positionScreen.y *= invW;
      positionScreen.z *= invW;
      vertex.visible = positionScreen.x >= -1 && positionScreen.x <= 1 && positionScreen.y >= -1 && positionScreen.y <= 1 && positionScreen.z >= -1 && positionScreen.z <= 1;
    }

    function pushVertex(x, y, z) {
      _vertex = getNextVertexInPool();

      _vertex.position.set(x, y, z);

      projectVertex(_vertex);
    }

    function pushNormal(x, y, z) {
      normals.push(x, y, z);
    }

    function pushColor(r, g, b) {
      colors.push(r, g, b);
    }

    function pushUv(x, y) {
      uvs.push(x, y);
    }

    function checkTriangleVisibility(v1, v2, v3) {
      if (v1.visible === true || v2.visible === true || v3.visible === true) return true;
      _points3[0] = v1.positionScreen;
      _points3[1] = v2.positionScreen;
      _points3[2] = v3.positionScreen;
      return _clipBox.intersectsBox(_boundingBox.setFromPoints(_points3));
    }

    function checkBackfaceCulling(v1, v2, v3) {
      return (v3.positionScreen.x - v1.positionScreen.x) * (v2.positionScreen.y - v1.positionScreen.y) - (v3.positionScreen.y - v1.positionScreen.y) * (v2.positionScreen.x - v1.positionScreen.x) < 0;
    }

    function pushLine(a, b) {
      var v1 = _vertexPool[a];
      var v2 = _vertexPool[b]; // Clip

      v1.positionScreen.copy(v1.position).applyMatrix4(_modelViewProjectionMatrix);
      v2.positionScreen.copy(v2.position).applyMatrix4(_modelViewProjectionMatrix);

      if (clipLine(v1.positionScreen, v2.positionScreen) === true) {
        // Perform the perspective divide
        v1.positionScreen.multiplyScalar(1 / v1.positionScreen.w);
        v2.positionScreen.multiplyScalar(1 / v2.positionScreen.w);
        _line = getNextLineInPool();
        _line.id = object.id;

        _line.v1.copy(v1);

        _line.v2.copy(v2);

        _line.z = Math.max(v1.positionScreen.z, v2.positionScreen.z);
        _line.renderOrder = object.renderOrder;
        _line.material = object.material;

        if (object.material.vertexColors) {
          _line.vertexColors[0].fromArray(colors, a * 3);

          _line.vertexColors[1].fromArray(colors, b * 3);
        }

        _renderData.elements.push(_line);
      }
    }

    function pushTriangle(a, b, c, material) {
      var v1 = _vertexPool[a];
      var v2 = _vertexPool[b];
      var v3 = _vertexPool[c];
      if (checkTriangleVisibility(v1, v2, v3) === false) return;

      if (material.side === THREE.DoubleSide || checkBackfaceCulling(v1, v2, v3) === true) {
        _face = getNextFaceInPool();
        _face.id = object.id;

        _face.v1.copy(v1);

        _face.v2.copy(v2);

        _face.v3.copy(v3);

        _face.z = (v1.positionScreen.z + v2.positionScreen.z + v3.positionScreen.z) / 3;
        _face.renderOrder = object.renderOrder; // face normal

        _vector3.subVectors(v3.position, v2.position);

        _vector4.subVectors(v1.position, v2.position);

        _vector3.cross(_vector4);

        _face.normalModel.copy(_vector3);

        _face.normalModel.applyMatrix3(normalMatrix).normalize();

        for (var i = 0; i < 3; i++) {
          var normal = _face.vertexNormalsModel[i];
          normal.fromArray(normals, arguments[i] * 3);
          normal.applyMatrix3(normalMatrix).normalize();
          var uv = _face.uvs[i];
          uv.fromArray(uvs, arguments[i] * 2);
        }

        _face.vertexNormalsLength = 3;
        _face.material = material;

        if (material.vertexColors) {
          _face.color.fromArray(colors, a * 3);
        }

        _renderData.elements.push(_face);
      }
    }

    return {
      setObject: setObject,
      projectVertex: projectVertex,
      checkTriangleVisibility: checkTriangleVisibility,
      checkBackfaceCulling: checkBackfaceCulling,
      pushVertex: pushVertex,
      pushNormal: pushNormal,
      pushColor: pushColor,
      pushUv: pushUv,
      pushLine: pushLine,
      pushTriangle: pushTriangle
    };
  };

  var renderList = new RenderList();

  function projectObject(object) {
    if (object.visible === false) return;

    if (object instanceof THREE.Light) {
      _renderData.lights.push(object);
    } else if (object instanceof THREE.Mesh || object instanceof THREE.Line || object instanceof THREE.Points) {
      if (object.material.visible === false) return;
      if (object.frustumCulled === true && _frustum.intersectsObject(object) === false) return;
      addObject(object);
    } else if (object instanceof THREE.Sprite) {
      if (object.material.visible === false) return;
      if (object.frustumCulled === true && _frustum.intersectsSprite(object) === false) return;
      addObject(object);
    }

    var children = object.children;

    for (var i = 0, l = children.length; i < l; i++) {
      projectObject(children[i]);
    }
  }

  function addObject(object) {
    _object = getNextObjectInPool();
    _object.id = object.id;
    _object.object = object;

    _vector3.setFromMatrixPosition(object.matrixWorld);

    _vector3.applyMatrix4(_viewProjectionMatrix);

    _object.z = _vector3.z;
    _object.renderOrder = object.renderOrder;

    _renderData.objects.push(_object);
  }

  this.projectScene = function (scene, camera, sortObjects, sortElements) {
    _faceCount = 0;
    _lineCount = 0;
    _spriteCount = 0;
    _renderData.elements.length = 0;
    if (scene.autoUpdate === true) scene.updateMatrixWorld();
    if (camera.parent === null) camera.updateMatrixWorld();

    _viewMatrix.copy(camera.matrixWorldInverse);

    _viewProjectionMatrix.multiplyMatrices(camera.projectionMatrix, _viewMatrix);

    _frustum.setFromProjectionMatrix(_viewProjectionMatrix); //


    _objectCount = 0;
    _renderData.objects.length = 0;
    _renderData.lights.length = 0;
    projectObject(scene);

    if (sortObjects === true) {
      _renderData.objects.sort(painterSort);
    } //


    var objects = _renderData.objects;

    for (var o = 0, ol = objects.length; o < ol; o++) {
      var object = objects[o].object;
      var geometry = object.geometry;
      renderList.setObject(object);
      _modelMatrix = object.matrixWorld;
      _vertexCount = 0;

      if (object instanceof THREE.Mesh) {
        if (geometry instanceof THREE.BufferGeometry) {
          var material = object.material;

          var isMultiMaterial = _Array$isArray(material);

          var attributes = geometry.attributes;
          var groups = geometry.groups;
          if (attributes.position === undefined) continue;
          var positions = attributes.position.array;

          for (var i = 0, l = positions.length; i < l; i += 3) {
            var x = positions[i];
            var y = positions[i + 1];
            var z = positions[i + 2];

            if (material.morphTargets === true) {
              var morphTargets = geometry.morphAttributes.position;
              var morphTargetsRelative = geometry.morphTargetsRelative;
              var morphInfluences = object.morphTargetInfluences;

              for (var t = 0, tl = morphTargets.length; t < tl; t++) {
                var influence = morphInfluences[t];
                if (influence === 0) continue;
                var target = morphTargets[t];

                if (morphTargetsRelative) {
                  x += target.getX(i / 3) * influence;
                  y += target.getY(i / 3) * influence;
                  z += target.getZ(i / 3) * influence;
                } else {
                  x += (target.getX(i / 3) - positions[i]) * influence;
                  y += (target.getY(i / 3) - positions[i + 1]) * influence;
                  z += (target.getZ(i / 3) - positions[i + 2]) * influence;
                }
              }
            }

            renderList.pushVertex(x, y, z);
          }

          if (attributes.normal !== undefined) {
            var normals = attributes.normal.array;

            for (var i = 0, l = normals.length; i < l; i += 3) {
              renderList.pushNormal(normals[i], normals[i + 1], normals[i + 2]);
            }
          }

          if (attributes.color !== undefined) {
            var colors = attributes.color.array;

            for (var i = 0, l = colors.length; i < l; i += 3) {
              renderList.pushColor(colors[i], colors[i + 1], colors[i + 2]);
            }
          }

          if (attributes.uv !== undefined) {
            var uvs = attributes.uv.array;

            for (var i = 0, l = uvs.length; i < l; i += 2) {
              renderList.pushUv(uvs[i], uvs[i + 1]);
            }
          }

          if (geometry.index !== null) {
            var indices = geometry.index.array;

            if (groups.length > 0) {
              for (var g = 0; g < groups.length; g++) {
                var group = groups[g];
                material = isMultiMaterial === true ? object.material[group.materialIndex] : object.material;
                if (material === undefined) continue;

                for (var i = group.start, l = group.start + group.count; i < l; i += 3) {
                  renderList.pushTriangle(indices[i], indices[i + 1], indices[i + 2], material);
                }
              }
            } else {
              for (var i = 0, l = indices.length; i < l; i += 3) {
                renderList.pushTriangle(indices[i], indices[i + 1], indices[i + 2], material);
              }
            }
          } else {
            if (groups.length > 0) {
              for (var g = 0; g < groups.length; g++) {
                var group = groups[g];
                material = isMultiMaterial === true ? object.material[group.materialIndex] : object.material;
                if (material === undefined) continue;

                for (var i = group.start, l = group.start + group.count; i < l; i += 3) {
                  renderList.pushTriangle(i, i + 1, i + 2, material);
                }
              }
            } else {
              for (var i = 0, l = positions.length / 3; i < l; i += 3) {
                renderList.pushTriangle(i, i + 1, i + 2, material);
              }
            }
          }
        } else if (geometry instanceof THREE.Geometry) {
          var vertices = geometry.vertices;
          var faces = geometry.faces;
          var faceVertexUvs = geometry.faceVertexUvs[0];

          _normalMatrix.getNormalMatrix(_modelMatrix);

          var material = object.material;

          var isMultiMaterial = _Array$isArray(material);

          for (var v = 0, vl = vertices.length; v < vl; v++) {
            var vertex = vertices[v];

            _vector3.copy(vertex);

            if (material.morphTargets === true) {
              var morphTargets = geometry.morphTargets;
              var morphInfluences = object.morphTargetInfluences;

              for (var t = 0, tl = morphTargets.length; t < tl; t++) {
                var influence = morphInfluences[t];
                if (influence === 0) continue;
                var target = morphTargets[t];
                var targetVertex = target.vertices[v];
                _vector3.x += (targetVertex.x - vertex.x) * influence;
                _vector3.y += (targetVertex.y - vertex.y) * influence;
                _vector3.z += (targetVertex.z - vertex.z) * influence;
              }
            }

            renderList.pushVertex(_vector3.x, _vector3.y, _vector3.z);
          }

          for (var f = 0, fl = faces.length; f < fl; f++) {
            var face = faces[f];
            material = isMultiMaterial === true ? object.material[face.materialIndex] : object.material;
            if (material === undefined) continue;
            var side = material.side;
            var v1 = _vertexPool[face.a];
            var v2 = _vertexPool[face.b];
            var v3 = _vertexPool[face.c];
            if (renderList.checkTriangleVisibility(v1, v2, v3) === false) continue;
            var visible = renderList.checkBackfaceCulling(v1, v2, v3);

            if (side !== THREE.DoubleSide) {
              if (side === THREE.FrontSide && visible === false) continue;
              if (side === THREE.BackSide && visible === true) continue;
            }

            _face = getNextFaceInPool();
            _face.id = object.id;

            _face.v1.copy(v1);

            _face.v2.copy(v2);

            _face.v3.copy(v3);

            _face.normalModel.copy(face.normal);

            if (visible === false && (side === THREE.BackSide || side === THREE.DoubleSide)) {
              _face.normalModel.negate();
            }

            _face.normalModel.applyMatrix3(_normalMatrix).normalize();

            var faceVertexNormals = face.vertexNormals;

            for (var n = 0, nl = Math.min(faceVertexNormals.length, 3); n < nl; n++) {
              var normalModel = _face.vertexNormalsModel[n];
              normalModel.copy(faceVertexNormals[n]);

              if (visible === false && (side === THREE.BackSide || side === THREE.DoubleSide)) {
                normalModel.negate();
              }

              normalModel.applyMatrix3(_normalMatrix).normalize();
            }

            _face.vertexNormalsLength = faceVertexNormals.length;
            var vertexUvs = faceVertexUvs[f];

            if (vertexUvs !== undefined) {
              for (var u = 0; u < 3; u++) {
                _face.uvs[u].copy(vertexUvs[u]);
              }
            }

            _face.color = face.color;
            _face.material = material;
            _face.z = (v1.positionScreen.z + v2.positionScreen.z + v3.positionScreen.z) / 3;
            _face.renderOrder = object.renderOrder;

            _renderData.elements.push(_face);
          }
        }
      } else if (object instanceof THREE.Line) {
        _modelViewProjectionMatrix.multiplyMatrices(_viewProjectionMatrix, _modelMatrix);

        if (geometry instanceof THREE.BufferGeometry) {
          var attributes = geometry.attributes;

          if (attributes.position !== undefined) {
            var positions = attributes.position.array;

            for (var i = 0, l = positions.length; i < l; i += 3) {
              renderList.pushVertex(positions[i], positions[i + 1], positions[i + 2]);
            }

            if (attributes.color !== undefined) {
              var colors = attributes.color.array;

              for (var i = 0, l = colors.length; i < l; i += 3) {
                renderList.pushColor(colors[i], colors[i + 1], colors[i + 2]);
              }
            }

            if (geometry.index !== null) {
              var indices = geometry.index.array;

              for (var i = 0, l = indices.length; i < l; i += 2) {
                renderList.pushLine(indices[i], indices[i + 1]);
              }
            } else {
              var step = object instanceof THREE.LineSegments ? 2 : 1;

              for (var i = 0, l = positions.length / 3 - 1; i < l; i += step) {
                renderList.pushLine(i, i + 1);
              }
            }
          }
        } else if (geometry instanceof THREE.Geometry) {
          var vertices = object.geometry.vertices;
          if (vertices.length === 0) continue;
          v1 = getNextVertexInPool();
          v1.positionScreen.copy(vertices[0]).applyMatrix4(_modelViewProjectionMatrix);
          var step = object instanceof THREE.LineSegments ? 2 : 1;

          for (var v = 1, vl = vertices.length; v < vl; v++) {
            v1 = getNextVertexInPool();
            v1.positionScreen.copy(vertices[v]).applyMatrix4(_modelViewProjectionMatrix);
            if ((v + 1) % step > 0) continue;
            v2 = _vertexPool[_vertexCount - 2];

            _clippedVertex1PositionScreen.copy(v1.positionScreen);

            _clippedVertex2PositionScreen.copy(v2.positionScreen);

            if (clipLine(_clippedVertex1PositionScreen, _clippedVertex2PositionScreen) === true) {
              // Perform the perspective divide
              _clippedVertex1PositionScreen.multiplyScalar(1 / _clippedVertex1PositionScreen.w);

              _clippedVertex2PositionScreen.multiplyScalar(1 / _clippedVertex2PositionScreen.w);

              _line = getNextLineInPool();
              _line.id = object.id;

              _line.v1.positionScreen.copy(_clippedVertex1PositionScreen);

              _line.v2.positionScreen.copy(_clippedVertex2PositionScreen);

              _line.z = Math.max(_clippedVertex1PositionScreen.z, _clippedVertex2PositionScreen.z);
              _line.renderOrder = object.renderOrder;
              _line.material = object.material;

              if (object.material.vertexColors) {
                _line.vertexColors[0].copy(object.geometry.colors[v]);

                _line.vertexColors[1].copy(object.geometry.colors[v - 1]);
              }

              _renderData.elements.push(_line);
            }
          }
        }
      } else if (object instanceof THREE.Points) {
        _modelViewProjectionMatrix.multiplyMatrices(_viewProjectionMatrix, _modelMatrix);

        if (geometry instanceof THREE.Geometry) {
          var vertices = object.geometry.vertices;

          for (var v = 0, vl = vertices.length; v < vl; v++) {
            var vertex = vertices[v];

            _vector4.set(vertex.x, vertex.y, vertex.z, 1);

            _vector4.applyMatrix4(_modelViewProjectionMatrix);

            pushPoint(_vector4, object, camera);
          }
        } else if (geometry instanceof THREE.BufferGeometry) {
          var attributes = geometry.attributes;

          if (attributes.position !== undefined) {
            var positions = attributes.position.array;

            for (var i = 0, l = positions.length; i < l; i += 3) {
              _vector4.set(positions[i], positions[i + 1], positions[i + 2], 1);

              _vector4.applyMatrix4(_modelViewProjectionMatrix);

              pushPoint(_vector4, object, camera);
            }
          }
        }
      } else if (object instanceof THREE.Sprite) {
        object.modelViewMatrix.multiplyMatrices(camera.matrixWorldInverse, object.matrixWorld);

        _vector4.set(_modelMatrix.elements[12], _modelMatrix.elements[13], _modelMatrix.elements[14], 1);

        _vector4.applyMatrix4(_viewProjectionMatrix);

        pushPoint(_vector4, object, camera);
      }
    }

    if (sortElements === true) {
      _renderData.elements.sort(painterSort);
    }

    return _renderData;
  };

  function pushPoint(_vector4, object, camera) {
    var invW = 1 / _vector4.w;
    _vector4.z *= invW;

    if (_vector4.z >= -1 && _vector4.z <= 1) {
      _sprite = getNextSpriteInPool();
      _sprite.id = object.id;
      _sprite.x = _vector4.x * invW;
      _sprite.y = _vector4.y * invW;
      _sprite.z = _vector4.z;
      _sprite.renderOrder = object.renderOrder;
      _sprite.object = object;
      _sprite.rotation = object.rotation;
      _sprite.scale.x = object.scale.x * Math.abs(_sprite.x - (_vector4.x + camera.projectionMatrix.elements[0]) / (_vector4.w + camera.projectionMatrix.elements[12]));
      _sprite.scale.y = object.scale.y * Math.abs(_sprite.y - (_vector4.y + camera.projectionMatrix.elements[5]) / (_vector4.w + camera.projectionMatrix.elements[13]));
      _sprite.material = object.material;

      _renderData.elements.push(_sprite);
    }
  } // Pools


  function getNextObjectInPool() {
    if (_objectCount === _objectPoolLength) {
      var object = new THREE.RenderableObject();

      _objectPool.push(object);

      _objectPoolLength++;
      _objectCount++;
      return object;
    }

    return _objectPool[_objectCount++];
  }

  function getNextVertexInPool() {
    if (_vertexCount === _vertexPoolLength) {
      var vertex = new THREE.RenderableVertex();

      _vertexPool.push(vertex);

      _vertexPoolLength++;
      _vertexCount++;
      return vertex;
    }

    return _vertexPool[_vertexCount++];
  }

  function getNextFaceInPool() {
    if (_faceCount === _facePoolLength) {
      var face = new THREE.RenderableFace();

      _facePool.push(face);

      _facePoolLength++;
      _faceCount++;
      return face;
    }

    return _facePool[_faceCount++];
  }

  function getNextLineInPool() {
    if (_lineCount === _linePoolLength) {
      var line = new THREE.RenderableLine();

      _linePool.push(line);

      _linePoolLength++;
      _lineCount++;
      return line;
    }

    return _linePool[_lineCount++];
  }

  function getNextSpriteInPool() {
    if (_spriteCount === _spritePoolLength) {
      var sprite = new THREE.RenderableSprite();

      _spritePool.push(sprite);

      _spritePoolLength++;
      _spriteCount++;
      return sprite;
    }

    return _spritePool[_spriteCount++];
  } //


  function painterSort(a, b) {
    if (a.renderOrder !== b.renderOrder) {
      return a.renderOrder - b.renderOrder;
    } else if (a.z !== b.z) {
      return b.z - a.z;
    } else if (a.id !== b.id) {
      return a.id - b.id;
    } else {
      return 0;
    }
  }

  function clipLine(s1, s2) {
    var alpha1 = 0,
        alpha2 = 1,
        // Calculate the boundary coordinate of each vertex for the near and far clip planes,
    // Z = -1 and Z = +1, respectively.
    bc1near = s1.z + s1.w,
        bc2near = s2.z + s2.w,
        bc1far = -s1.z + s1.w,
        bc2far = -s2.z + s2.w;

    if (bc1near >= 0 && bc2near >= 0 && bc1far >= 0 && bc2far >= 0) {
      // Both vertices lie entirely within all clip planes.
      return true;
    } else if (bc1near < 0 && bc2near < 0 || bc1far < 0 && bc2far < 0) {
      // Both vertices lie entirely outside one of the clip planes.
      return false;
    } else {
      // The line segment spans at least one clip plane.
      if (bc1near < 0) {
        // v1 lies outside the near plane, v2 inside
        alpha1 = Math.max(alpha1, bc1near / (bc1near - bc2near));
      } else if (bc2near < 0) {
        // v2 lies outside the near plane, v1 inside
        alpha2 = Math.min(alpha2, bc1near / (bc1near - bc2near));
      }

      if (bc1far < 0) {
        // v1 lies outside the far plane, v2 inside
        alpha1 = Math.max(alpha1, bc1far / (bc1far - bc2far));
      } else if (bc2far < 0) {
        // v2 lies outside the far plane, v2 inside
        alpha2 = Math.min(alpha2, bc1far / (bc1far - bc2far));
      }

      if (alpha2 < alpha1) {
        // The line segment spans two boundaries, but is outside both of them.
        // (This can't happen when we're only clipping against just near/far but good
        //  to leave the check here for future usage if other clip planes are added.)
        return false;
      } else {
        // Update the s1 and s2 vertices to match the clipped line segment.
        s1.lerp(s2, alpha1);
        s2.lerp(s1, 1 - alpha2);
        return true;
      }
    }
  }
};