@cesium/engine/Source/Core/Cesium3DTilesTerrainGeometryProcessor.js

CesiumJS is a JavaScript library for creating 3D globes and 2D maps in a web browser without a plugin.

import { MeshoptDecoder } from "meshoptimizer";
import AttributeCompression from "./AttributeCompression.js";
import Axis from "../Scene/Axis.js";
import AxisAlignedBoundingBox from "./AxisAlignedBoundingBox.js";
import binarySearch from "./binarySearch.js";
import BoundingSphere from "./BoundingSphere.js";
import Cartesian2 from "./Cartesian2.js";
import Cartesian3 from "./Cartesian3.js";
import Cartographic from "./Cartographic.js";
import CesiumMath from "./Math.js";
import Check from "./Check.js";
import ComponentDatatype from "./ComponentDatatype.js";
import Ellipsoid from "./Ellipsoid.js";
import EllipsoidalOccluder from "./EllipsoidalOccluder.js";
import Frozen from "./Frozen.js";
import Matrix4 from "./Matrix4.js";
import OrientedBoundingBox from "./OrientedBoundingBox.js";
import Rectangle from "./Rectangle.js";
import TerrainEncoding from "./TerrainEncoding.js";
import TerrainMesh from "./TerrainMesh.js";
import TerrainProvider from "./TerrainProvider.js";
import Transforms from "./Transforms.js";
import WebMercatorProjection from "./WebMercatorProjection.js";

/**
 * Contains functions to create a mesh from 3D Tiles terrain data.
 *
 * @namespace Cesium3DTilesTerrainGeometryProcessor
 *
 * @private
 */
const Cesium3DTilesTerrainGeometryProcessor = {};

/**
 * Contains information about geometry-related vertex arrays in a glTF asset.
 * @private
 * @typedef GltfInfo
 *
 * @property {Float32Array} positions The decoded position attributes.
 * @property {Float32Array|undefined} normals The decoded normal attributes, or <code>undefined</code> if the glTF has no normals.
 * @property {Uint16Array|Uint32Array} indices The decoded indices.
 * @property {Uint16Array|Uint32Array} edgeIndicesWest The edge indices along the West side of the tile.
 * @property {Uint16Array|Uint32Array} edgeIndicesSouth The edge indices along the South side of the tile.
 * @property {Uint16Array|Uint32Array} edgeIndicesEast The edge indices along the East side of the tile.
 * @property {Uint16Array|Uint32Array} edgeIndicesNorth The edge indices along the North side of the tile.
 */

const scratchGltfInfo = {
  positions: undefined,
  normals: undefined,
  indices: undefined,
  edgeIndicesWest: undefined,
  edgeIndicesSouth: undefined,
  edgeIndicesEast: undefined,
  edgeIndicesNorth: undefined,
};

const scratchCenterCartographic = new Cartographic();
const scratchCenterCartesian = new Cartesian3();
const scratchEnuToEcef = new Matrix4();
const scratchEcefToEnu = new Matrix4();
const scratchTilesetTransform = new Matrix4();
const scratchMinimumPositionENU = new Cartesian3();
const scratchMaximumPositionENU = new Cartesian3();
const scratchPosLocal = new Cartesian3();
const scratchPosEcef = new Cartesian3();
const scratchCartographic = new Cartographic();
const scratchUV = new Cartesian2();
const scratchNormal = new Cartesian3();
const scratchNormalOct = new Cartesian2();
const scratchGeodeticSurfaceNormal = new Cartesian3();
const scratchPosEnu = new Cartesian3();

/**
 * Compares two edge indices for sorting.
 * @private
 * @param {number} a The first edge index.
 * @param {number} b The second edge index.
 * @returns {number} A negative number if <code>a</code> is less than <code>b</code>, a positive number if <code>a</code> is greater than <code>b</code>, or zero if they are equal.
 */
const sortedEdgeCompare = function (a, b) {
  return a - b;
};

/**
 * @typedef {object} Cesium3DTilesTerrainGeometryProcessor.CreateMeshOptions
 * @property {Ellipsoid} ellipsoid The ellipsoid.
 * @property {Rectangle} rectangle The rectangle covered by the tile.
 * @property {boolean} hasVertexNormals <code>true</code> if the tile has vertex normals.
 * @property {boolean} hasWebMercatorT <code>true</code> if the tile has Web Mercator T coordinates.
 * @property {Object.<string,*>} gltf The glTF JSON of the tile.
 * @property {number} minimumHeight The minimum height of the tile.
 * @property {number} maximumHeight The maximum height of the tile.
 * @property {BoundingSphere} boundingSphere The bounding sphere of the tile.
 * @property {OrientedBoundingBox} orientedBoundingBox The oriented bounding box of the tile.
 * @property {Cartesian3} horizonOcclusionPoint The horizon occlusion point of the tile.
 * @property {number} skirtHeight The height of the skirts.
 * @property {number} [exaggeration=1.0] The scale used to exaggerate the terrain.
 * @property {number} [exaggerationRelativeHeight=0.0] The height relative to which terrain is exaggerated.
 */

/**
 * Creates a {@link TerrainMesh} from this terrain data.
 * @function
 *
 * @private
 *
 * @param {Cesium3DTilesTerrainGeometryProcessor.CreateMeshOptions} options An object describing options for mesh creation.
 * @returns {Promise.<TerrainMesh>} A promise to a terrain mesh.
 */
Cesium3DTilesTerrainGeometryProcessor.createMesh = async function (options) {
  options = options ?? Frozen.EMPTY_OBJECT;
  const {
    exaggeration = 1.0,
    exaggerationRelativeHeight = 0.0,
    hasVertexNormals,
    hasWebMercatorT,
    gltf,
    minimumHeight,
    maximumHeight,
    skirtHeight,
  } = options;

  //>>includeStart('debug', pragmas.debug);
  Check.typeOf.object("options.ellipsoid", options.ellipsoid);
  Check.typeOf.object("options.rectangle", options.rectangle);
  Check.typeOf.bool("options.hasVertexNormals", hasVertexNormals);
  Check.typeOf.bool("options.hasWebMercatorT", hasWebMercatorT);
  Check.typeOf.object("options.gltf", gltf);
  Check.typeOf.number("options.minimumHeight", minimumHeight);
  Check.typeOf.number("options.maximumHeight", maximumHeight);
  Check.typeOf.object("options.boundingSphere", options.boundingSphere);
  Check.typeOf.object(
    "options.orientedBoundingBox",
    options.orientedBoundingBox,
  );
  Check.typeOf.object(
    "options.horizonOcclusionPoint",
    options.horizonOcclusionPoint,
  );
  Check.typeOf.number("options.skirtHeight", skirtHeight);
  //>>includeEnd('debug');

  const hasExaggeration = exaggeration !== 1.0;
  const hasGeodeticSurfaceNormals = hasExaggeration;

  const boundingSphere = BoundingSphere.clone(
    options.boundingSphere,
    new BoundingSphere(),
  );
  const orientedBoundingBox = OrientedBoundingBox.clone(
    options.orientedBoundingBox,
    new OrientedBoundingBox(),
  );
  const horizonOcclusionPoint = Cartesian3.clone(
    options.horizonOcclusionPoint,
    new Cartesian3(),
  );
  const ellipsoid = Ellipsoid.clone(options.ellipsoid, new Ellipsoid());
  const rectangle = Rectangle.clone(options.rectangle, new Rectangle());

  const hasMeshOptCompression =
    gltf.extensionsRequired !== undefined &&
    gltf.extensionsRequired.indexOf("EXT_meshopt_compression") !== -1;

  const decoderPromise = hasMeshOptCompression
    ? MeshoptDecoder.ready
    : Promise.resolve(undefined);

  await decoderPromise;

  const tileMinLongitude = rectangle.west;
  const tileMinLatitude = rectangle.south;
  const tileMaxLatitude = rectangle.north;
  const tileLengthLongitude = rectangle.width;
  const tileLengthLatitude = rectangle.height;

  const approximateCenterCartographic = Rectangle.center(
    rectangle,
    scratchCenterCartographic,
  );
  approximateCenterCartographic.height = 0.5 * (minimumHeight + maximumHeight);

  const approximateCenterPosition = Cartographic.toCartesian(
    approximateCenterCartographic,
    ellipsoid,
    scratchCenterCartesian,
  );

  const enuToEcef = Transforms.eastNorthUpToFixedFrame(
    approximateCenterPosition,
    ellipsoid,
    scratchEnuToEcef,
  );
  const ecefToEnu = Matrix4.inverseTransformation(enuToEcef, scratchEcefToEnu);

  let tilesetTransform = Matrix4.unpack(
    gltf.nodes[0].matrix,
    0,
    scratchTilesetTransform,
  );

  tilesetTransform = Matrix4.multiply(
    Axis.Y_UP_TO_Z_UP,
    tilesetTransform,
    tilesetTransform,
  );

  const gltfInfo = decodeGltf(gltf, hasVertexNormals, scratchGltfInfo);

  const skirtVertexCount = TerrainProvider.getSkirtVertexCount(
    gltfInfo.edgeIndicesWest,
    gltfInfo.edgeIndicesSouth,
    gltfInfo.edgeIndicesEast,
    gltfInfo.edgeIndicesNorth,
  );

  const positionsLocalWithoutSkirts = gltfInfo.positions;
  const normalsWithoutSkirts = gltfInfo.normals;
  const indicesWithoutSkirts = gltfInfo.indices;
  const vertexCountWithoutSkirts = positionsLocalWithoutSkirts.length / 3;
  const vertexCountWithSkirts = vertexCountWithoutSkirts + skirtVertexCount;
  const indexCountWithoutSkirts = indicesWithoutSkirts.length;
  const skirtIndexCount =
    TerrainProvider.getSkirtIndexCountWithFilledCorners(skirtVertexCount);

  // For consistency with glTF spec, 16 bit index buffer can't contain 65535
  const SizedIndexTypeWithSkirts =
    vertexCountWithSkirts <= 65535 ? Uint16Array : Uint32Array;
  // Make the index buffer large enough that we can add in the skirt indices later
  const indexBufferWithSkirts = new SizedIndexTypeWithSkirts(
    indexCountWithoutSkirts + skirtIndexCount,
  );
  indexBufferWithSkirts.set(indicesWithoutSkirts);

  const westIndices = new SizedIndexTypeWithSkirts(gltfInfo.edgeIndicesWest);
  const southIndices = new SizedIndexTypeWithSkirts(gltfInfo.edgeIndicesSouth);
  const eastIndices = new SizedIndexTypeWithSkirts(gltfInfo.edgeIndicesEast);
  const northIndices = new SizedIndexTypeWithSkirts(gltfInfo.edgeIndicesNorth);

  const sortedWestIndices = new SizedIndexTypeWithSkirts(westIndices).sort();
  const sortedSouthIndices = new SizedIndexTypeWithSkirts(southIndices).sort();
  const sortedEastIndices = new SizedIndexTypeWithSkirts(eastIndices).sort();
  const sortedNorthIndices = new SizedIndexTypeWithSkirts(northIndices).sort();

  const southMercatorAngle =
    WebMercatorProjection.geodeticLatitudeToMercatorAngle(tileMinLatitude);
  const northMercatorAngle =
    WebMercatorProjection.geodeticLatitudeToMercatorAngle(tileMaxLatitude);

  const oneOverMercatorHeight = 1.0 / (northMercatorAngle - southMercatorAngle);

  // Use a terrain encoding without quantization.
  // This is just an easier way to save intermediate state
  let minPosEnu = Cartesian3.fromElements(
    Number.POSITIVE_INFINITY,
    Number.POSITIVE_INFINITY,
    Number.POSITIVE_INFINITY,
    scratchMinimumPositionENU,
  );
  let maxPosEnu = Cartesian3.fromElements(
    Number.NEGATIVE_INFINITY,
    Number.NEGATIVE_INFINITY,
    Number.NEGATIVE_INFINITY,
    scratchMaximumPositionENU,
  );
  const tempTerrainEncoding = new TerrainEncoding(
    boundingSphere.center,
    undefined,
    undefined,
    undefined,
    undefined,
    hasVertexNormals,
    hasWebMercatorT,
    hasGeodeticSurfaceNormals,
    exaggeration,
    exaggerationRelativeHeight,
  );

  const tempBufferStride = tempTerrainEncoding.stride;
  const tempBuffer = new Float32Array(vertexCountWithSkirts * tempBufferStride);
  let tempBufferOffset = 0;

  for (let i = 0; i < vertexCountWithoutSkirts; i++) {
    const posLocal = Cartesian3.unpack(
      positionsLocalWithoutSkirts,
      i * 3,
      scratchPosLocal,
    );

    const posECEF = Matrix4.multiplyByPoint(
      tilesetTransform,
      posLocal,
      scratchPosEcef,
    );

    const cartographic = Cartographic.fromCartesian(
      posECEF,
      ellipsoid,
      scratchCartographic,
    );

    const { longitude, latitude, height } = cartographic;

    // If a vertex is an edge vertex we already know its exact UV and don't need to derive it from the position (which can have accuracy issues).

    let u = (longitude - tileMinLongitude) / tileLengthLongitude;
    let v = (latitude - tileMinLatitude) / tileLengthLatitude;

    // Clamp the UVs to the valid range
    // This should only happen when the cartesian to cartographic conversion introduces error on a point that is already very close the edge
    u = CesiumMath.clamp(u, 0.0, 1.0);
    v = CesiumMath.clamp(v, 0.0, 1.0);

    if (binarySearch(sortedWestIndices, i, sortedEdgeCompare) >= 0) {
      u = 0.0;
    } else if (binarySearch(sortedEastIndices, i, sortedEdgeCompare) >= 0) {
      u = 1.0;
    }

    if (binarySearch(sortedSouthIndices, i, sortedEdgeCompare) >= 0) {
      v = 0.0;
    } else if (binarySearch(sortedNorthIndices, i, sortedEdgeCompare) >= 0) {
      v = 1.0;
    }

    const uv = Cartesian2.fromElements(u, v, scratchUV);

    let normalOct;
    if (hasVertexNormals) {
      let normal = Cartesian3.unpack(
        normalsWithoutSkirts,
        i * 3,
        scratchNormal,
      );
      normal = Matrix4.multiplyByPointAsVector(
        tilesetTransform,
        normal,
        scratchNormal,
      );

      normal = Cartesian3.normalize(normal, scratchNormal);

      normalOct = AttributeCompression.octEncode(normal, scratchNormalOct);
    }

    let webMercatorT;
    if (hasWebMercatorT) {
      const mercatorAngle =
        WebMercatorProjection.geodeticLatitudeToMercatorAngle(latitude);
      webMercatorT =
        (mercatorAngle - southMercatorAngle) * oneOverMercatorHeight;
    }

    let geodeticSurfaceNormal;
    if (hasGeodeticSurfaceNormals) {
      geodeticSurfaceNormal = ellipsoid.geodeticSurfaceNormal(
        posECEF,
        scratchGeodeticSurfaceNormal,
      );
    }

    tempBufferOffset = tempTerrainEncoding.encode(
      tempBuffer,
      tempBufferOffset,
      posECEF,
      uv,
      height,
      normalOct,
      webMercatorT,
      geodeticSurfaceNormal,
    );

    const posEnu = Matrix4.multiplyByPoint(ecefToEnu, posECEF, scratchPosEnu);
    minPosEnu = Cartesian3.minimumByComponent(posEnu, minPosEnu, minPosEnu);
    maxPosEnu = Cartesian3.maximumByComponent(posEnu, maxPosEnu, maxPosEnu);
  }

  const mesh = new TerrainMesh(
    Cartesian3.clone(tempTerrainEncoding.center, new Cartesian3()),
    tempBuffer,
    indexBufferWithSkirts,
    indexCountWithoutSkirts,
    vertexCountWithoutSkirts,
    minimumHeight,
    maximumHeight,
    BoundingSphere.clone(boundingSphere, new BoundingSphere()),
    Cartesian3.clone(horizonOcclusionPoint, new Cartesian3()),
    tempBufferStride,
    OrientedBoundingBox.clone(orientedBoundingBox, new OrientedBoundingBox()),
    tempTerrainEncoding,
    westIndices,
    southIndices,
    eastIndices,
    northIndices,
  );

  addSkirtsToMesh(
    mesh,
    rectangle,
    ellipsoid,
    minPosEnu,
    maxPosEnu,
    enuToEcef,
    ecefToEnu,
    skirtHeight,
  );

  return Promise.resolve(mesh);
};

const scratchMinUV = new Cartesian2();
const scratchMaxUV = new Cartesian2();
const scratchPolygonIndices = new Array(6);
const scratchUvA = new Cartesian2();
const scratchUvB = new Cartesian2();
const scratchUvC = new Cartesian2();
const scratchNormalA = new Cartesian3();
const scratchNormalB = new Cartesian3();
const scratchNormalC = new Cartesian3();
const scratchCenterCartographicUpsample = new Cartographic();
const scratchCenterCartesianUpsample = new Cartesian3();
const scratchCartographicSkirt = new Cartographic();
const scratchCartographicUpsample = new Cartographic();
const scratchPosEcefSkirt = new Cartesian3();
const scratchPosEcefUpsample = new Cartesian3();
const scratchPosEnuSkirt = new Cartesian3();
const scratchPosEnuUpsample = new Cartesian3();
const scratchMinimumPositionENUSkirt = new Cartesian3();
const scratchMaximumPositionENUSkirt = new Cartesian3();
const scratchMinimumPositionENUUpsample = new Cartesian3();
const scratchMaximumPositionENUUpsample = new Cartesian3();
const scratchEnuToEcefUpsample = new Matrix4();
const scratchEcefToEnuUpsample = new Matrix4();
const scratchUVSkirt = new Cartesian2();
const scratchUVUpsample = new Cartesian2();
const scratchHorizonOcclusionPoint = new Cartesian3();
const scratchBoundingSphere = new BoundingSphere();
const scratchOrientedBoundingBox = new OrientedBoundingBox();
const scratchAABBEnuSkirt = new AxisAlignedBoundingBox();
const scratchNormalUpsample = new Cartesian3();
const scratchNormalOctSkirt = new Cartesian2();
const scratchNormalOctUpsample = new Cartesian2();
const scratchGeodeticSurfaceNormalSkirt = new Cartesian3();
const scratchGeodeticSurfaceNormalUpsample = new Cartesian3();

/**
 * Decode the position attributes from a glTF object.
 * @private
 * @param {Object.<string,*>} gltf The glTF JSON.
 * @returns {Float32Array} The decoded positions, as a flattened array of x, y, z values.
 */
function decodePositions(gltf) {
  const primitive = gltf.meshes[0].primitives[0];
  const accessor = gltf.accessors[primitive.attributes["POSITION"]];
  const bufferView = gltf.bufferViews[accessor.bufferView];
  const positionCount = accessor.count;

  const bufferViewMeshOpt = bufferView.extensions
    ? bufferView.extensions["EXT_meshopt_compression"]
    : undefined;

  if (bufferViewMeshOpt === undefined) {
    const buffer = gltf.buffers[bufferView.buffer].extras._pipeline.source;

    return new Float32Array(
      buffer.buffer,
      buffer.byteOffset + // offset from the start of the glb
        (bufferView.byteOffset ?? 0) +
        (accessor.byteOffset ?? 0),
      positionCount * 3,
    );
  }

  const buffer = gltf.buffers[bufferViewMeshOpt.buffer].extras._pipeline.source;

  const compressedBuffer = new Uint8Array(
    buffer.buffer,
    buffer.byteOffset + // offset from the start of the glb
      (bufferViewMeshOpt.byteOffset ?? 0) +
      (accessor.byteOffset ?? 0),
    bufferViewMeshOpt.byteLength,
  );

  const positionByteLength = bufferViewMeshOpt.byteStride;
  const PositionType = positionByteLength === 4 ? Uint8Array : Uint16Array;
  const positionsResult = new PositionType(positionCount * 4);
  MeshoptDecoder.decodeVertexBuffer(
    new Uint8Array(positionsResult.buffer),
    positionCount,
    positionByteLength,
    compressedBuffer,
  );

  const positionStorageValueMax =
    (1 << (positionsResult.BYTES_PER_ELEMENT * 8)) - 1;
  const positions = new Float32Array(positionCount * 3);
  for (let p = 0; p < positionCount; p++) {
    // only the first 3 components are used
    positions[p * 3 + 0] = positionsResult[p * 4 + 0] / positionStorageValueMax;
    positions[p * 3 + 1] = positionsResult[p * 4 + 1] / positionStorageValueMax;
    positions[p * 3 + 2] = positionsResult[p * 4 + 2] / positionStorageValueMax;
    // fourth component is not used
  }
  return positions;
}

/**
 * Decode the normal attributes from a glTF object.
 * @private
 * @param {Object.<string,*>} gltf The glTF JSON.
 * @returns {Float32Array} The decoded normals, as a flattened array of x, y, z values.
 */
function decodeNormals(gltf) {
  const primitive = gltf.meshes[0].primitives[0];
  const accessor = gltf.accessors[primitive.attributes["NORMAL"]];
  const bufferView = gltf.bufferViews[accessor.bufferView];
  const normalCount = accessor.count;

  const bufferViewMeshOpt = bufferView.extensions
    ? bufferView.extensions["EXT_meshopt_compression"]
    : undefined;

  if (bufferViewMeshOpt === undefined) {
    const buffer = gltf.buffers[bufferView.buffer].extras._pipeline.source;

    return new Float32Array(
      buffer.buffer,
      buffer.byteOffset + // offset from the start of the glb
        (bufferView.byteOffset ?? 0) +
        (accessor.byteOffset ?? 0),
      normalCount * 3,
    );
  }

  const buffer = gltf.buffers[bufferViewMeshOpt.buffer].extras._pipeline.source;

  const compressedBuffer = new Uint8Array(
    buffer.buffer,
    buffer.byteOffset + // offset from the start of the glb
      (bufferViewMeshOpt.byteOffset ?? 0) +
      (accessor.byteOffset ?? 0),
    bufferViewMeshOpt.byteLength,
  );

  const normalByteLength = bufferViewMeshOpt.byteStride;
  const normalsResult = new Int8Array(normalCount * normalByteLength);

  MeshoptDecoder.decodeVertexBuffer(
    new Uint8Array(normalsResult.buffer),
    normalCount,
    normalByteLength,
    compressedBuffer,
  );

  const normals = new Float32Array(normalCount * 3);
  for (let i = 0; i < normalCount; i++) {
    // AttributeCompression.octDecodeInRange is not compatible with KHR_mesh_quantization, so do the oct decode manually
    // The quantization puts values between -127 and +127, but clamp in case it has -128
    // The third component is unused until normals support non-8-bit quantization
    // The fourth component is always unused
    let octX = Math.max(normalsResult[i * 4 + 0] / 127.0, -1.0);
    let octY = Math.max(normalsResult[i * 4 + 1] / 127.0, -1.0);
    const octZ = 1.0 - (Math.abs(octX) + Math.abs(octY));

    if (octZ < 0.0) {
      const oldX = octX;
      const oldY = octY;
      octX = (1.0 - Math.abs(oldY)) * CesiumMath.signNotZero(oldX);
      octY = (1.0 - Math.abs(oldX)) * CesiumMath.signNotZero(oldY);
    }

    let normal = scratchNormal;
    normal.x = octX;
    normal.y = octY;
    normal.z = octZ;
    normal = Cartesian3.normalize(normal, scratchNormal);

    normals[i * 3 + 0] = normal.x;
    normals[i * 3 + 1] = normal.y;
    normals[i * 3 + 2] = normal.z;
  }
  return normals;
}

/**
 * Decode the index attributes from a glTF object.
 * @private
 * @param {Object.<string,*>} gltf The glTF JSON.
 * @returns {Uint16Array|Uint32Array} An array of indices.
 */
function decodeIndices(gltf) {
  const primitive = gltf.meshes[0].primitives[0];
  const accessor = gltf.accessors[primitive.indices];
  const bufferView = gltf.bufferViews[accessor.bufferView];
  const indexCount = accessor.count;

  const SizedIndexType =
    accessor.componentType === ComponentDatatype.UNSIGNED_SHORT
      ? Uint16Array
      : Uint32Array;

  const bufferViewMeshOpt = bufferView.extensions
    ? bufferView.extensions["EXT_meshopt_compression"]
    : undefined;

  if (bufferViewMeshOpt === undefined) {
    const buffer = gltf.buffers[bufferView.buffer].extras._pipeline.source;
    return new SizedIndexType(
      buffer.buffer,
      buffer.byteOffset + // offset from the glb
        (bufferView.byteOffset ?? 0) +
        (accessor.byteOffset ?? 0),
      indexCount,
    );
  }

  const buffer = gltf.buffers[bufferViewMeshOpt.buffer].extras._pipeline.source;
  const compressedBuffer = new Uint8Array(
    buffer.buffer,
    buffer.byteOffset + // offset from the start of the glb
      (bufferViewMeshOpt.byteOffset ?? 0) +
      (accessor.byteOffset ?? 0),
    bufferViewMeshOpt.byteLength,
  );

  const indices = new SizedIndexType(indexCount);
  MeshoptDecoder.decodeIndexBuffer(
    new Uint8Array(indices.buffer),
    indexCount,
    bufferViewMeshOpt.byteStride,
    compressedBuffer,
  );
  return indices;
}

/**
 * Decode the edge index attributes from a glTF object.
 * @private
 * @param {Object.<string,*>} gltf The glTF JSON.
 * @param {string} name The name of the edge indices to decode.
 * @returns {Uint16Array|Uint32Array} An array of edge indices.
 */
function decodeEdgeIndices(gltf, name) {
  const primitive = gltf.meshes[0].primitives[0];
  const accessor = gltf.accessors[primitive.extensions.CESIUM_tile_edges[name]];
  const bufferView = gltf.bufferViews[accessor.bufferView];

  const indexCount = accessor.count;
  const SizedIndexType =
    accessor.componentType === ComponentDatatype.UNSIGNED_SHORT
      ? Uint16Array
      : Uint32Array;

  const bufferViewMeshOpt = bufferView.extensions
    ? bufferView.extensions["EXT_meshopt_compression"]
    : undefined;

  if (bufferViewMeshOpt === undefined) {
    const buffer = gltf.buffers[bufferView.buffer].extras._pipeline.source;

    return new SizedIndexType(
      buffer.buffer,
      buffer.byteOffset + // offset from the glb
        (bufferView.byteOffset ?? 0) +
        (accessor.byteOffset ?? 0),
      indexCount,
    );
  }

  const buffer = gltf.buffers[bufferViewMeshOpt.buffer].extras._pipeline.source;
  const compressedBuffer = new Uint8Array(
    buffer.buffer,
    buffer.byteOffset + // offset from the start of the glb
      (bufferViewMeshOpt.byteOffset ?? 0) +
      (accessor.byteOffset ?? 0),
    bufferViewMeshOpt.byteLength,
  );

  const indices = new SizedIndexType(indexCount);
  const indexByteLength = bufferViewMeshOpt.byteStride;
  MeshoptDecoder.decodeIndexSequence(
    new Uint8Array(indices.buffer),
    indexCount,
    indexByteLength,
    compressedBuffer,
  );
  return indices;
}

/**
 * Decodes geometry-related vertex arrays from a glTF asset.
 * @private
 * @param {Object.<string,*>} gltf The glTF JSON.
 * @param {boolean} hasNormals <code>true</code> if the glTF has normal attributes.
 * @param {GltfInfo} result The object to store the decoded arrays.
 * @returns {GltfInfo} The decoded geometry info.
 */
function decodeGltf(gltf, hasNormals, result) {
  result.positions = decodePositions(gltf);
  result.normals = hasNormals ? decodeNormals(gltf) : undefined;
  result.indices = decodeIndices(gltf);
  result.edgeIndicesWest = decodeEdgeIndices(gltf, "left");
  result.edgeIndicesSouth = decodeEdgeIndices(gltf, "bottom");
  result.edgeIndicesEast = decodeEdgeIndices(gltf, "right");
  result.edgeIndicesNorth = decodeEdgeIndices(gltf, "top");
  return result;
}

/**
 * @typedef {object} Cesium3DTilesTerrainGeometryProcessor.UpsampleMeshOptions
 * @property {boolean} isEastChild <code>true</code> if the tile is the east child of its parent.
 * @property {boolean} isNorthChild <code>true</code> if the tile is the north child of its parent.
 * @property {Rectangle} rectangle The rectangle covered by the tile.
 * @property {Ellipsoid} ellipsoid The ellipsoid.
 * @property {number} skirtHeight The height of the skirts.
 * @property {Float32Array} parentVertices The parent tile's vertex buffer.
 * @property {Uint8Array|Uint16Array|Uint32Array} parentIndices The parent tile's index buffer.
 * @property {number} parentVertexCountWithoutSkirts The number of vertices in the parent tile excluding skirts.
 * @property {number} parentIndexCountWithoutSkirts The number of indices in the parent tile excluding skirts.
 * @property {number} parentMinimumHeight The minimum height of the parent tile.
 * @property {number} parentMaximumHeight The maximum height of the parent tile.
 * @property {TerrainEncoding} parentEncoding The parent tile's terrain encoding.
 */

/**
 * Upsamples a parent tile's mesh to create a higher-detail child tile's mesh.
 *
 * Overview: Only include triangles that are inside the UV clipping region.
 * If a triangle is partly outside, it will be clipped at the border.
 * The clipping function returns a polygon where each point is a barycentric coordinate of the input triangle.
 * Most of the time the triangle will not be clipped, so the polygon will be the three barycentric coordinates of the input triangle.
 * If the triangle is completely outside the clipping region, the polygon will have no points and will be ignored.
 * If the triangle is clipped, the polygon will have between four and six points and needs to be triangulated.
 *  Vertex data for points that fall inside the triangle will be interpolated using the barycentric coordinates.
 * Each vertex in the polygon is added to the new vertex list, with some special handling to avoid duplicate points between triangles.
 *
 * @private
 * @param {Cesium3DTilesTerrainGeometryProcessor.UpsampleMeshOptions} options An object describing options for mesh upsampling.
 * @returns {TerrainMesh} The upsampled terrain mesh.
 */
Cesium3DTilesTerrainGeometryProcessor.upsampleMesh = function (options) {
  options = options ?? Frozen.EMPTY_OBJECT;

  const {
    isEastChild,
    isNorthChild,
    parentMinimumHeight,
    parentMaximumHeight,
    skirtHeight,
  } = options;

  //>>includeStart('debug', pragmas.debug)
  Check.typeOf.bool("options.isEastChild", isEastChild);
  Check.typeOf.bool("options.isNorthChild", isNorthChild);
  Check.typeOf.object("options.parentVertices", options.parentVertices);
  Check.typeOf.object("options.parentIndices", options.parentIndices);
  Check.typeOf.number(
    "options.parentVertexCountWithoutSkirts",
    options.parentVertexCountWithoutSkirts,
  );
  Check.typeOf.number(
    "options.parentIndexCountWithoutSkirts",
    options.parentIndexCountWithoutSkirts,
  );
  Check.typeOf.number("options.parentMinimumHeight", parentMinimumHeight);
  Check.typeOf.number("options.parentMaximumHeight", parentMaximumHeight);
  Check.typeOf.object("options.parentEncoding", options.parentEncoding);
  Check.typeOf.object("options.rectangle", options.rectangle);
  Check.typeOf.number("options.skirtHeight", skirtHeight);
  Check.typeOf.object("options.ellipsoid", options.ellipsoid);
  //>>includeEnd('debug');

  const indexCount = options.parentIndexCountWithoutSkirts;
  const indices = options.parentIndices;
  const vertexCount = options.parentVertexCountWithoutSkirts;
  const vertexBuffer = options.parentVertices;
  const encoding = TerrainEncoding.clone(
    options.parentEncoding,
    new TerrainEncoding(),
  );
  const hasVertexNormals = encoding.hasVertexNormals;
  const hasWebMercatorT = encoding.hasWebMercatorT;
  const exaggeration = encoding.exaggeration;
  const exaggerationRelativeHeight = encoding.exaggerationRelativeHeight;
  const hasExaggeration = exaggeration !== 1.0;
  const hasGeodeticSurfaceNormals = hasExaggeration;
  const upsampleRectangle = Rectangle.clone(options.rectangle, new Rectangle());
  const ellipsoid = Ellipsoid.clone(options.ellipsoid);

  const upsampledTriIDs = [];
  const upsampledUVs = [];
  const upsampledBarys = [];
  const upsampledIndices = [];
  const upsampledWestIndices = [];
  const upsampledSouthIndices = [];
  const upsampledEastIndices = [];
  const upsampledNorthIndices = [];

  clipTileFromQuadrant(
    isEastChild,
    isNorthChild,
    indexCount,
    indices,
    vertexCount,
    vertexBuffer,
    encoding,
    upsampledIndices,
    upsampledWestIndices,
    upsampledSouthIndices,
    upsampledEastIndices,
    upsampledNorthIndices,
    upsampledTriIDs,
    upsampledBarys,
    upsampledUVs,
  );

  // Don't know the min and max height of the upsampled positions yet,
  // so calculate a center point from the parent's min and max height
  const approximateCenterCartographic = Rectangle.center(
    upsampleRectangle,
    scratchCenterCartographicUpsample,
  );
  approximateCenterCartographic.height =
    0.5 * (parentMinimumHeight + parentMaximumHeight);
  const approximateCenterPosition = Cartographic.toCartesian(
    approximateCenterCartographic,
    ellipsoid,
    scratchCenterCartesianUpsample,
  );

  const upsampledVertexCountWithoutSkirts = upsampledTriIDs.length;
  const upsampledTerrainEncoding = new TerrainEncoding(
    approximateCenterPosition,
    undefined,
    undefined,
    undefined,
    undefined,
    hasVertexNormals,
    hasWebMercatorT,
    hasGeodeticSurfaceNormals,
    exaggeration,
    exaggerationRelativeHeight,
  );
  const upsampledVertexBufferStride = upsampledTerrainEncoding.stride;

  const upsampledSkirtVertexCount = TerrainProvider.getSkirtVertexCount(
    upsampledWestIndices,
    upsampledSouthIndices,
    upsampledEastIndices,
    upsampledNorthIndices,
  );
  const upsampledVertexCountWithSkirts =
    upsampledVertexCountWithoutSkirts + upsampledSkirtVertexCount;
  const upsampledIndexCountWithoutSkirts = upsampledIndices.length;
  const upsampledSkirtIndexCount =
    TerrainProvider.getSkirtIndexCountWithFilledCorners(
      upsampledSkirtVertexCount,
    );
  const upsampledIndexCountWithSkirts =
    upsampledIndexCountWithoutSkirts + upsampledSkirtIndexCount;
  // For consistency with glTF spec, 16 bit index buffer can't contain 65535
  const SizedIndexTypeWithSkirts =
    upsampledVertexCountWithSkirts <= 65535 ? Uint16Array : Uint32Array;
  const upsampledIndexBuffer = new SizedIndexTypeWithSkirts(
    upsampledIndexCountWithSkirts,
  );
  upsampledIndexBuffer.set(upsampledIndices);

  const upsampledWestIndicesBuffer = new SizedIndexTypeWithSkirts(
    upsampledWestIndices,
  );

  const upsampledSouthIndicesBuffer = new SizedIndexTypeWithSkirts(
    upsampledSouthIndices,
  );

  const upsampledEastIndicesBuffer = new SizedIndexTypeWithSkirts(
    upsampledEastIndices,
  );

  const upsampledNorthIndicesBuffer = new SizedIndexTypeWithSkirts(
    upsampledNorthIndices,
  );

  const upsampledVertexBuffer = new Float32Array(
    upsampledVertexCountWithSkirts * upsampledVertexBufferStride,
  );
  let upsampledVertexBufferOffset = 0;

  const enuToEcef = Transforms.eastNorthUpToFixedFrame(
    approximateCenterPosition,
    ellipsoid,
    scratchEnuToEcefUpsample,
  );
  const ecefToEnu = Matrix4.inverseTransformation(
    enuToEcef,
    scratchEcefToEnuUpsample,
  );

  const minimumLongitude = upsampleRectangle.west;
  const maximumLongitude = upsampleRectangle.east;
  const minimumLatitude = upsampleRectangle.south;
  const maximumLatitude = upsampleRectangle.north;

  const southMercatorAngle =
    WebMercatorProjection.geodeticLatitudeToMercatorAngle(minimumLatitude);
  const northMercatorAngle =
    WebMercatorProjection.geodeticLatitudeToMercatorAngle(maximumLatitude);
  const oneOverMercatorHeight = 1.0 / (northMercatorAngle - southMercatorAngle);

  let minimumHeight = Number.POSITIVE_INFINITY;
  let maximumHeight = Number.NEGATIVE_INFINITY;

  let minPosEnu = Cartesian3.fromElements(
    Number.POSITIVE_INFINITY,
    Number.POSITIVE_INFINITY,
    Number.POSITIVE_INFINITY,
    scratchMinimumPositionENUUpsample,
  );
  let maxPosEnu = Cartesian3.fromElements(
    Number.NEGATIVE_INFINITY,
    Number.NEGATIVE_INFINITY,
    Number.NEGATIVE_INFINITY,
    scratchMaximumPositionENUUpsample,
  );

  for (let i = 0; i < upsampledVertexCountWithoutSkirts; i++) {
    const triId = upsampledTriIDs[i];
    const indexA = indices[triId * 3 + 0];
    const indexB = indices[triId * 3 + 1];
    const indexC = indices[triId * 3 + 2];

    const uv = scratchUVUpsample;
    uv.x = upsampledUVs[i * 2 + 0];
    uv.y = upsampledUVs[i * 2 + 1];
    const u = uv.x;
    const v = uv.y;

    const baryA = upsampledBarys[i * 2 + 0];
    const baryB = upsampledBarys[i * 2 + 1];
    const baryC = 1.0 - baryA - baryB;

    const heightA = encoding.decodeHeight(vertexBuffer, indexA);
    const heightB = encoding.decodeHeight(vertexBuffer, indexB);
    const heightC = encoding.decodeHeight(vertexBuffer, indexC);

    const height = heightA * baryA + heightB * baryB + heightC * baryC;
    minimumHeight = Math.min(height, minimumHeight);
    maximumHeight = Math.max(height, maximumHeight);

    const lon = CesiumMath.lerp(minimumLongitude, maximumLongitude, u);
    const lat = CesiumMath.lerp(minimumLatitude, maximumLatitude, v);
    const carto = Cartographic.fromRadians(
      lon,
      lat,
      height,
      scratchCartographicUpsample,
    );
    const position = Cartographic.toCartesian(
      carto,
      ellipsoid,
      scratchPosEcefUpsample,
    );

    const posEnu = Matrix4.multiplyByPoint(
      ecefToEnu,
      position,
      scratchPosEnuUpsample,
    );
    minPosEnu = Cartesian3.minimumByComponent(posEnu, minPosEnu, minPosEnu);
    maxPosEnu = Cartesian3.maximumByComponent(posEnu, maxPosEnu, maxPosEnu);

    let normalOct;
    if (hasVertexNormals) {
      const normalA = encoding.decodeNormal(
        vertexBuffer,
        indexA,
        scratchNormalA,
      );
      const normalB = encoding.decodeNormal(
        vertexBuffer,
        indexB,
        scratchNormalB,
      );
      const normalC = encoding.decodeNormal(
        vertexBuffer,
        indexC,
        scratchNormalC,
      );

      let normal = Cartesian3.fromElements(
        normalA.x * baryA + normalB.x * baryB + normalC.x * baryC,
        normalA.y * baryA + normalB.y * baryB + normalC.y * baryC,
        normalA.z * baryA + normalB.z * baryB + normalC.z * baryC,
        scratchNormalUpsample,
      );
      normal = Cartesian3.normalize(normal, scratchNormalUpsample);
      normalOct = AttributeCompression.octEncode(
        normal,
        scratchNormalOctUpsample,
      );
    }

    let webMercatorT;
    if (hasWebMercatorT) {
      const mercatorAngle =
        WebMercatorProjection.geodeticLatitudeToMercatorAngle(lat);
      webMercatorT =
        (mercatorAngle - southMercatorAngle) * oneOverMercatorHeight;
    }

    let geodeticSurfaceNormal;
    if (hasGeodeticSurfaceNormals) {
      geodeticSurfaceNormal = ellipsoid.geodeticSurfaceNormal(
        position,
        scratchGeodeticSurfaceNormalUpsample,
      );
    }

    upsampledVertexBufferOffset = upsampledTerrainEncoding.encode(
      upsampledVertexBuffer,
      upsampledVertexBufferOffset,
      position,
      uv,
      height,
      normalOct,
      webMercatorT,
      geodeticSurfaceNormal,
    );
  }

  // Now generate the more tight-fitting bounding volumes that are used for culling and other things
  const orientedBoundingBox = OrientedBoundingBox.fromRectangle(
    upsampleRectangle,
    minimumHeight,
    maximumHeight,
    ellipsoid,
    scratchOrientedBoundingBox,
  );
  const boundingSphere = BoundingSphere.fromVertices(
    upsampledVertexBuffer,
    upsampledTerrainEncoding.center,
    upsampledVertexBufferStride,
    scratchBoundingSphere,
  );
  const occluder = new EllipsoidalOccluder(ellipsoid);
  const horizonOcclusionPoint =
    occluder.computeHorizonCullingPointFromVerticesPossiblyUnderEllipsoid(
      upsampledTerrainEncoding.center, // vector from ellipsoid center to horizon occlusion point
      upsampledVertexBuffer,
      upsampledVertexBufferStride,
      upsampledTerrainEncoding.center,
      minimumHeight,
      scratchHorizonOcclusionPoint,
    );

  const upsampledMesh = new TerrainMesh(
    Cartesian3.clone(upsampledTerrainEncoding.center, new Cartesian3()),
    upsampledVertexBuffer,
    upsampledIndexBuffer,
    upsampledIndexCountWithoutSkirts,
    upsampledVertexCountWithoutSkirts,
    minimumHeight,
    maximumHeight,
    BoundingSphere.clone(boundingSphere),
    Cartesian3.clone(horizonOcclusionPoint),
    upsampledVertexBufferStride,
    OrientedBoundingBox.clone(orientedBoundingBox),
    upsampledTerrainEncoding,
    upsampledWestIndicesBuffer,
    upsampledSouthIndicesBuffer,
    upsampledEastIndicesBuffer,
    upsampledNorthIndicesBuffer,
  );

  addSkirtsToMesh(
    upsampledMesh,
    upsampleRectangle,
    ellipsoid,
    minPosEnu,
    maxPosEnu,
    enuToEcef,
    ecefToEnu,
    skirtHeight,
  );

  return upsampledMesh;
};

/**
 * Helper function that adds skirts to a TerrainMesh. The mesh's vertex and index
 * buffers are expected to be pre-allocated to fit the skirts.
 * The mesh's vertex buffer must have quantization disabled.
 * If the final quantization changes, a new vertex buffer will be allocated using the new quantization.
 * Currently skirts do not affect the tile's bounding volume.
 * @private
 * @param {TerrainMesh} mesh
 * @param {Rectangle} rectangle
 * @param {Ellipsoid} ellipsoid
 * @param {Cartesian3} enuMinimum
 * @param {Cartesian3} enuMaximum
 * @param {Matrix4} enuToEcef
 * @param {Matrix4} ecefToEnu
 * @param {number} skirtHeight
 */
function addSkirtsToMesh(
  mesh,
  rectangle,
  ellipsoid,
  enuMinimum,
  enuMaximum,
  enuToEcef,
  ecefToEnu,
  skirtHeight,
) {
  const { encoding } = mesh;
  const vertexStride = encoding.stride;
  const vertexBuffer = mesh.vertices;
  const {
    hasVertexNormals,
    hasWebMercatorT,
    exaggeration,
    exaggerationRelativeHeight,
  } = encoding;
  const hasExaggeration = exaggeration !== 1.0;
  const hasGeodeticSurfaceNormals = hasExaggeration;

  const vertexCountWithoutSkirts = mesh.vertexCountWithoutSkirts;
  let vertexBufferOffset = vertexCountWithoutSkirts * vertexStride;
  const vertexCountWithSkirts = vertexBuffer.length / vertexStride;
  const skirtVertexCount = vertexCountWithSkirts - vertexCountWithoutSkirts;
  const indices = mesh.indices;
  const indexCountWithoutSkirts = mesh.indexCountWithoutSkirts;

  const westIndices = mesh.westIndicesSouthToNorth;
  const southIndices = mesh.southIndicesEastToWest;
  const eastIndices = mesh.eastIndicesNorthToSouth;
  const northIndices = mesh.northIndicesWestToEast;

  TerrainProvider.addSkirtIndicesWithFilledCorners(
    westIndices,
    southIndices,
    eastIndices,
    northIndices,
    vertexCountWithoutSkirts,
    indices,
    indexCountWithoutSkirts,
  );

  const westOffset = 0;
  const southOffset = westOffset + westIndices.length;
  const eastOffset = southOffset + southIndices.length;
  const northOffset = eastOffset + eastIndices.length;
  const edges = [westIndices, southIndices, eastIndices, northIndices];
  const edgeIndexOffset = [westOffset, southOffset, eastOffset, northOffset];
  const edgeLongitudeSign = [-1.0, 0.0, +1.0, 0.0];
  const edgeLatitudeSign = [0.0, -1.0, 0.0, +1.0];

  const minimumPositionENUWithSkirts = Cartesian3.clone(
    enuMinimum,
    scratchMinimumPositionENUSkirt,
  );
  const maximumPositionENUWithSkirts = Cartesian3.clone(
    enuMaximum,
    scratchMaximumPositionENUSkirt,
  );
  const maximumHeight = mesh.maximumHeight;
  const minimumHeightWithSkirts = mesh.minimumHeight - skirtHeight;
  for (let skirtId = 0; skirtId < skirtVertexCount; skirtId++) {
    let side = 0;
    for (side = 0; side < 3; side++) {
      if (skirtId < edgeIndexOffset[side + 1]) {
        break;
      }
    }
    const vertexIndex = edges[side][skirtId - edgeIndexOffset[side]];

    const uv = encoding.decodeTextureCoordinates(
      vertexBuffer,
      vertexIndex,
      scratchUVSkirt,
    );

    const skirtLonLatOffsetPercent = 0.0001;
    const longitudeT =
      uv.x + edgeLongitudeSign[side] * skirtLonLatOffsetPercent;
    const latitudeT = uv.y + edgeLatitudeSign[side] * skirtLonLatOffsetPercent;

    const longitude = CesiumMath.lerp(
      rectangle.west,
      rectangle.east,
      longitudeT,
    );
    // Don't offset the skirt past the poles, it will screw up the cartographic -> cartesian
    const latitude = CesiumMath.clamp(
      CesiumMath.lerp(rectangle.south, rectangle.north, latitudeT),
      -CesiumMath.PI_OVER_TWO,
      +CesiumMath.PI_OVER_TWO,
    );

    const vertHeight = encoding.decodeHeight(vertexBuffer, vertexIndex);
    const height = vertHeight - skirtHeight;

    const cartographic = Cartographic.fromRadians(
      longitude,
      latitude,
      height,
      scratchCartographicSkirt,
    );

    const positionEcef = Cartographic.toCartesian(
      cartographic,
      ellipsoid,
      scratchPosEcefSkirt,
    );

    let normalOct;
    if (hasVertexNormals) {
      normalOct = encoding.getOctEncodedNormal(
        vertexBuffer,
        vertexIndex,
        scratchNormalOctSkirt,
      );
    }

    let webMercatorT;
    if (hasWebMercatorT) {
      webMercatorT = encoding.decodeWebMercatorT(vertexBuffer, vertexIndex);
    }

    let geodeticSurfaceNormal;
    if (hasGeodeticSurfaceNormals) {
      geodeticSurfaceNormal = ellipsoid.geodeticSurfaceNormal(
        positionEcef,
        scratchGeodeticSurfaceNormalSkirt,
      );
    }

    vertexBufferOffset = encoding.encode(
      vertexBuffer,
      vertexBufferOffset,
      positionEcef,
      uv,
      height,
      normalOct,
      webMercatorT,
      geodeticSurfaceNormal,
    );

    const positionENU = Matrix4.multiplyByPoint(
      ecefToEnu,
      positionEcef,
      scratchPosEnuSkirt,
    );
    Cartesian3.minimumByComponent(
      positionENU,
      minimumPositionENUWithSkirts,
      minimumPositionENUWithSkirts,
    );
    Cartesian3.maximumByComponent(
      positionENU,
      maximumPositionENUWithSkirts,
      maximumPositionENUWithSkirts,
    );
  }

  const aabbEnuWithSkirts = AxisAlignedBoundingBox.fromCorners(
    minimumPositionENUWithSkirts,
    maximumPositionENUWithSkirts,
    scratchAABBEnuSkirt,
  );

  // Check if the final terrain encoding has a different quantization. If so,
  // the vertices need to be re-encoded with the new quantization. Otherwise,
  // use the vertex buffer as-is.
  const encodingWithSkirts = new TerrainEncoding(
    encoding.center,
    aabbEnuWithSkirts,
    minimumHeightWithSkirts,
    maximumHeight,
    enuToEcef,
    encoding.hasVertexNormals,
    encoding.hasWebMercatorT,
    hasGeodeticSurfaceNormals,
    exaggeration,
    exaggerationRelativeHeight,
  );
  if (encoding.quantization !== encodingWithSkirts.quantization) {
    const finalEncoding = encodingWithSkirts;
    const finalVertexStride = finalEncoding.stride;
    const finalVertexBuffer = new Float32Array(
      vertexCountWithSkirts * finalVertexStride,
    );
    let finalVertexBufferOffset = 0;
    for (let i = 0; i < vertexCountWithSkirts; i++) {
      finalVertexBufferOffset = finalEncoding.encode(
        finalVertexBuffer,
        finalVertexBufferOffset,
        encoding.decodePosition(vertexBuffer, i, scratchPosEcefSkirt),
        encoding.decodeTextureCoordinates(vertexBuffer, i, scratchUVSkirt),
        encoding.decodeHeight(vertexBuffer, i),
        encoding.hasVertexNormals
          ? encoding.getOctEncodedNormal(vertexBuffer, i, scratchNormalOctSkirt)
          : undefined,
        encoding.hasWebMercatorT
          ? encoding.decodeWebMercatorT(vertexBuffer, i)
          : undefined,
        encoding.hasGeodeticSurfaceNormals
          ? encoding.decodeGeodeticSurfaceNormal(
              vertexBuffer,
              i,
              scratchGeodeticSurfaceNormalSkirt,
            )
          : undefined,
      );
    }
    mesh.vertices = finalVertexBuffer;
    mesh.stride = finalVertexStride;
    mesh.encoding = finalEncoding;
  }

  return mesh;
}

const EDGE_ID_LEFT = 0;
const EDGE_ID_TOP = 1;
const EDGE_ID_RIGHT = 2;
const EDGE_ID_BOTTOM = 3;
const EDGE_COUNT = 4;

const scratchIntersection = new Cartesian3();

const scratchInBarys = [
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
];
const scratchInPoints = [
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
];

const scratchOutBarys = [
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
  new Cartesian3(),
];
const scratchOutPoints = [
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
  new Cartesian2(),
];

/**
 * Check if a given point is inside the limits of a box.
 * @private
 * @param {Cartesian2} boxMinimum The lower left corner of the box.
 * @param {Cartesian2} boxMaximum The upper right corner of the box.
 * @param {number} edgeId The ID of the edge to test against.
 * @param {Cartesian2} p The point to test.
 * @returns {number} Positive if inside, negative if outside, zero if on the edge.
 */
function inside(boxMinimum, boxMaximum, edgeId, p) {
  switch (edgeId) {
    case EDGE_ID_LEFT:
      return CesiumMath.sign(p.x - boxMinimum.x);
    case EDGE_ID_RIGHT:
      return CesiumMath.sign(boxMaximum.x - p.x);
    case EDGE_ID_BOTTOM:
      return CesiumMath.sign(p.y - boxMinimum.y);
    default:
      // EDGE_ID_TOP
      return CesiumMath.sign(boxMaximum.y - p.y);
  }
}

/**
 * Compute the intersection of a line segment against one edge of a box.
 * @private
 * @param {Cartesian2} boxMinimum The lower left corner of the box.
 * @param {Cartesian2} boxMaximum The upper right corner of the box.
 * @param {number} edgeId The ID of the edge to intersect against.
 * @param {Cartesian2} a The beginning of the line segment.
 * @param {Cartesian2} b The end of the line segment.
 * @param {Cartesian3} result The object into which to copy the result.
 * @returns {Cartesian3} The intersection point in 2D coordinates and the interpolation factor t as the third component.
 */
function intersect(boxMinimum, boxMaximum, edgeId, a, b, result) {
  let t, intersectX, intersectY;
  switch (edgeId) {
    case EDGE_ID_LEFT:
      t = (boxMinimum.x - a.x) / (b.x - a.x);
      intersectX = boxMinimum.x;
      intersectY = a.y + (b.y - a.y) * t;
      break;
    case EDGE_ID_RIGHT:
      t = (boxMaximum.x - a.x) / (b.x - a.x);
      intersectX = boxMaximum.x;
      intersectY = a.y + (b.y - a.y) * t;
      break;
    case EDGE_ID_BOTTOM:
      t = (boxMinimum.y - a.y) / (b.y - a.y);
      intersectX = a.x + (b.x - a.x) * t;
      intersectY = boxMinimum.y;
      break;
    default:
      // EDGE_ID_TOP
      t = (boxMaximum.y - a.y) / (b.y - a.y);
      intersectX = a.x + (b.x - a.x) * t;
      intersectY = boxMaximum.y;
      break;
  }
  return Cartesian3.fromElements(intersectX, intersectY, t, result);
}

/**
 * Coordinates of a quadrilateral resulting from clipping a triangle against a box.
 * @private
 * @typedef PolygonResult
 *
 * @property {number} length
 * @property {Cartesian2[]} coordinates A pre-allocated array of six 2D coordinates.
 * @property {Cartesian3[]} barycentricCoordinates A pre-allocated array of six barycentric coordinates.
 */

/**
 * A scratch polygon result for use in clipping.
 * @private
 * @type {PolygonResult}
 */
const scratchPolygon = {
  length: 0,
  coordinates: [
    new Cartesian2(),
    new Cartesian2(),
    new Cartesian2(),
    new Cartesian2(),
    new Cartesian2(),
    new Cartesian2(),
  ],
  barycentricCoordinates: [
    new Cartesian3(),
    new Cartesian3(),
    new Cartesian3(),
    new Cartesian3(),
    new Cartesian3(),
    new Cartesian3(),
  ],
};

/**
 * Clips a 2D triangle against axis-aligned edges of a box using the Sutherland-Hodgman
 * clipping algorithm. The resulting polygon will have between 0 and 6 vertices.
 *
 * @private
 * @param {number} edgeStart The first edge to clip against.
 * @param {number} edgeCount The number of edges to clip against, starting from edgeStart.
 * @param {Cartesian2} boxMinimum The bottom-left corner of the axis-aligned box.
 * @param {Cartesian2} boxMaximum The top-right corner of the axis-aligned box.
 * @param {Cartesian2} p0 The coordinates of the first vertex in the triangle, in counter-clockwise order.
 * @param {Cartesian2} p1 The coordinates of the second vertex in the triangle, in counter-clockwise order.
 * @param {Cartesian2} p2 The coordinates of the third vertex in the triangle, in counter-clockwise order.
 * @param {PolygonResult} result The object into which to copy the result.
 * @returns {PolygonResult} The polygon that results after the clip, specified as a list of coordinates in counter-clockwise order.
 */
function clipTriangleAgainstBoxEdgeRang