Cesium-Prequel/Source/Core/HeightmapTerrainData.js

import when from "../ThirdParty/when.js";
import BoundingSphere from "./BoundingSphere.js";
import Cartesian3 from "./Cartesian3.js";
import Check from "./Check.js";
import defaultValue from "./defaultValue.js";
import defined from "./defined.js";
import DeveloperError from "./DeveloperError.js";
import GeographicProjection from "./GeographicProjection.js";
import HeightmapEncoding from "./HeightmapEncoding.js";
import HeightmapTessellator from "./HeightmapTessellator.js";
import CesiumMath from "./Math.js";
import OrientedBoundingBox from "./OrientedBoundingBox.js";
import Rectangle from "./Rectangle.js";
import TaskProcessor from "./TaskProcessor.js";
import TerrainData from "./TerrainData.js";
import TerrainEncoding from "./TerrainEncoding.js";
import TerrainMesh from "./TerrainMesh.js";
import TerrainProvider from "./TerrainProvider.js";

/**
 * Terrain data for a single tile where the terrain data is represented as a heightmap.  A heightmap
 * is a rectangular array of heights in row-major order from north to south and west to east.
 *
 * @alias HeightmapTerrainData
 * @constructor
 *
 * @param {Object} options Object with the following properties:
 * @param {Int8Array|Uint8Array|Int16Array|Uint16Array|Int32Array|Uint32Array|Float32Array|Float64Array} options.buffer The buffer containing height data.
 * @param {Number} options.width The width (longitude direction) of the heightmap, in samples.
 * @param {Number} options.height The height (latitude direction) of the heightmap, in samples.
 * @param {Number} [options.childTileMask=15] A bit mask indicating which of this tile's four children exist.
 *                 If a child's bit is set, geometry will be requested for that tile as well when it
 *                 is needed.  If the bit is cleared, the child tile is not requested and geometry is
 *                 instead upsampled from the parent.  The bit values are as follows:
 *                 <table>
 *                  <tr><th>Bit Position</th><th>Bit Value</th><th>Child Tile</th></tr>
 *                  <tr><td>0</td><td>1</td><td>Southwest</td></tr>
 *                  <tr><td>1</td><td>2</td><td>Southeast</td></tr>
 *                  <tr><td>2</td><td>4</td><td>Northwest</td></tr>
 *                  <tr><td>3</td><td>8</td><td>Northeast</td></tr>
 *                 </table>
 * @param {Uint8Array} [options.waterMask] The water mask included in this terrain data, if any.  A water mask is a square
 *                     Uint8Array or image where a value of 255 indicates water and a value of 0 indicates land.
 *                     Values in between 0 and 255 are allowed as well to smoothly blend between land and water.
 * @param {Object} [options.structure] An object describing the structure of the height data.
 * @param {Number} [options.structure.heightScale=1.0] The factor by which to multiply height samples in order to obtain
 *                 the height above the heightOffset, in meters.  The heightOffset is added to the resulting
 *                 height after multiplying by the scale.
 * @param {Number} [options.structure.heightOffset=0.0] The offset to add to the scaled height to obtain the final
 *                 height in meters.  The offset is added after the height sample is multiplied by the
 *                 heightScale.
 * @param {Number} [options.structure.elementsPerHeight=1] The number of elements in the buffer that make up a single height
 *                 sample.  This is usually 1, indicating that each element is a separate height sample.  If
 *                 it is greater than 1, that number of elements together form the height sample, which is
 *                 computed according to the structure.elementMultiplier and structure.isBigEndian properties.
 * @param {Number} [options.structure.stride=1] The number of elements to skip to get from the first element of
 *                 one height to the first element of the next height.
 * @param {Number} [options.structure.elementMultiplier=256.0] The multiplier used to compute the height value when the
 *                 stride property is greater than 1.  For example, if the stride is 4 and the strideMultiplier
 *                 is 256, the height is computed as follows:
 *                 `height = buffer[index] + buffer[index + 1] * 256 + buffer[index + 2] * 256 * 256 + buffer[index + 3] * 256 * 256 * 256`
 *                 This is assuming that the isBigEndian property is false.  If it is true, the order of the
 *                 elements is reversed.
 * @param {Boolean} [options.structure.isBigEndian=false] Indicates endianness of the elements in the buffer when the
 *                  stride property is greater than 1.  If this property is false, the first element is the
 *                  low-order element.  If it is true, the first element is the high-order element.
 * @param {Number} [options.structure.lowestEncodedHeight] The lowest value that can be stored in the height buffer.  Any heights that are lower
 *                 than this value after encoding with the `heightScale` and `heightOffset` are clamped to this value.  For example, if the height
 *                 buffer is a `Uint16Array`, this value should be 0 because a `Uint16Array` cannot store negative numbers.  If this parameter is
 *                 not specified, no minimum value is enforced.
 * @param {Number} [options.structure.highestEncodedHeight] The highest value that can be stored in the height buffer.  Any heights that are higher
 *                 than this value after encoding with the `heightScale` and `heightOffset` are clamped to this value.  For example, if the height
 *                 buffer is a `Uint16Array`, this value should be `256 * 256 - 1` or 65535 because a `Uint16Array` cannot store numbers larger
 *                 than 65535.  If this parameter is not specified, no maximum value is enforced.
 * @param {HeightmapEncoding} [options.encoding=HeightmapEncoding.NONE] The encoding that is used on the buffer.
 * @param {Boolean} [options.createdByUpsampling=false] True if this instance was created by upsampling another instance;
 *                  otherwise, false.
 *
 *
 * @example
 * var buffer = ...
 * var heightBuffer = new Uint16Array(buffer, 0, that._heightmapWidth * that._heightmapWidth);
 * var childTileMask = new Uint8Array(buffer, heightBuffer.byteLength, 1)[0];
 * var waterMask = new Uint8Array(buffer, heightBuffer.byteLength + 1, buffer.byteLength - heightBuffer.byteLength - 1);
 * var terrainData = new Cesium.HeightmapTerrainData({
 *   buffer : heightBuffer,
 *   width : 65,
 *   height : 65,
 *   childTileMask : childTileMask,
 *   waterMask : waterMask
 * });
 *
 * @see TerrainData
 * @see QuantizedMeshTerrainData
 * @see GoogleEarthEnterpriseTerrainData
 */
function HeightmapTerrainData(options) {
  //>>includeStart('debug', pragmas.debug);
  if (!defined(options) || !defined(options.buffer)) {
    throw new DeveloperError("options.buffer is required.");
  }
  if (!defined(options.width)) {
    throw new DeveloperError("options.width is required.");
  }
  if (!defined(options.height)) {
    throw new DeveloperError("options.height is required.");
  }
  //>>includeEnd('debug');

  this._buffer = options.buffer;
  this._width = options.width;
  this._height = options.height;
  this._childTileMask = defaultValue(options.childTileMask, 15);
  this._encoding = defaultValue(options.encoding, HeightmapEncoding.NONE);

  var defaultStructure = HeightmapTessellator.DEFAULT_STRUCTURE;
  var structure = options.structure;
  if (!defined(structure)) {
    structure = defaultStructure;
  } else if (structure !== defaultStructure) {
    structure.heightScale = defaultValue(
      structure.heightScale,
      defaultStructure.heightScale
    );
    structure.heightOffset = defaultValue(
      structure.heightOffset,
      defaultStructure.heightOffset
    );
    structure.elementsPerHeight = defaultValue(
      structure.elementsPerHeight,
      defaultStructure.elementsPerHeight
    );
    structure.stride = defaultValue(structure.stride, defaultStructure.stride);
    structure.elementMultiplier = defaultValue(
      structure.elementMultiplier,
      defaultStructure.elementMultiplier
    );
    structure.isBigEndian = defaultValue(
      structure.isBigEndian,
      defaultStructure.isBigEndian
    );
  }

  this._structure = structure;
  this._createdByUpsampling = defaultValue(options.createdByUpsampling, false);
  this._waterMask = options.waterMask;

  this._skirtHeight = undefined;
  this._bufferType =
    this._encoding === HeightmapEncoding.LERC
      ? Float32Array
      : this._buffer.constructor;
  this._mesh = undefined;
}

Object.defineProperties(HeightmapTerrainData.prototype, {
  /**
   * An array of credits for this tile.
   * @memberof HeightmapTerrainData.prototype
   * @type {Credit[]}
   */
  credits: {
    get: function () {
      return undefined;
    },
  },
  /**
   * The water mask included in this terrain data, if any.  A water mask is a square
   * Uint8Array or image where a value of 255 indicates water and a value of 0 indicates land.
   * Values in between 0 and 255 are allowed as well to smoothly blend between land and water.
   * @memberof HeightmapTerrainData.prototype
   * @type {Uint8Array|HTMLImageElement|HTMLCanvasElement}
   */
  waterMask: {
    get: function () {
      return this._waterMask;
    },
  },

  childTileMask: {
    get: function () {
      return this._childTileMask;
    },
  },
});

var createMeshTaskName = "createVerticesFromHeightmap";
var createMeshTaskProcessorNoThrottle = new TaskProcessor(createMeshTaskName);
var createMeshTaskProcessorThrottle = new TaskProcessor(
  createMeshTaskName,
  TerrainData.maximumAsynchronousTasks
);

/**
 * Creates a {@link TerrainMesh} from this terrain data.
 *
 * @private
 *
 * @param {Object} options Object with the following properties:
 * @param {TilingScheme} options.tilingScheme The tiling scheme to which this tile belongs.
 * @param {Number} options.x The X coordinate of the tile for which to create the terrain data.
 * @param {Number} options.y The Y coordinate of the tile for which to create the terrain data.
 * @param {Number} options.level The level of the tile for which to create the terrain data.
 * @param {Number} [options.exaggeration=1.0] The scale used to exaggerate the terrain.
 * @param {Boolean} [options.throttle=true] If true, indicates that this operation will need to be retried if too many asynchronous mesh creations are already in progress.
 * @returns {Promise.<TerrainMesh>|undefined} A promise for the terrain mesh, or undefined if too many
 *          asynchronous mesh creations are already in progress and the operation should
 *          be retried later.
 */
HeightmapTerrainData.prototype.createMesh = function (options) {
  options = defaultValue(options, defaultValue.EMPTY_OBJECT);

  //>>includeStart('debug', pragmas.debug);
  Check.typeOf.object("options.tilingScheme", options.tilingScheme);
  Check.typeOf.number("options.x", options.x);
  Check.typeOf.number("options.y", options.y);
  Check.typeOf.number("options.level", options.level);
  //>>includeEnd('debug');

  var tilingScheme = options.tilingScheme;
  var x = options.x;
  var y = options.y;
  var level = options.level;
  var exaggeration = defaultValue(options.exaggeration, 1.0);
  var throttle = defaultValue(options.throttle, true);

  var ellipsoid = tilingScheme.ellipsoid;
  var nativeRectangle = tilingScheme.tileXYToNativeRectangle(x, y, level);
  var rectangle = tilingScheme.tileXYToRectangle(x, y, level);

  // Compute the center of the tile for RTC rendering.
  var center = ellipsoid.cartographicToCartesian(Rectangle.center(rectangle));

  var structure = this._structure;

  var levelZeroMaxError = TerrainProvider.getEstimatedLevelZeroGeometricErrorForAHeightmap(
    ellipsoid,
    this._width,
    tilingScheme.getNumberOfXTilesAtLevel(0)
  );
  var thisLevelMaxError = levelZeroMaxError / (1 << level);
  this._skirtHeight = Math.min(thisLevelMaxError * 4.0, 1000.0);

  var createMeshTaskProcessor = throttle
    ? createMeshTaskProcessorThrottle
    : createMeshTaskProcessorNoThrottle;

  var verticesPromise = createMeshTaskProcessor.scheduleTask({
    heightmap: this._buffer,
    structure: structure,
    includeWebMercatorT: true,
    width: this._width,
    height: this._height,
    nativeRectangle: nativeRectangle,
    rectangle: rectangle,
    relativeToCenter: center,
    ellipsoid: ellipsoid,
    skirtHeight: this._skirtHeight,
    isGeographic: tilingScheme.projection instanceof GeographicProjection,
    exaggeration: exaggeration,
    encoding: this._encoding,
  });

  if (!defined(verticesPromise)) {
    // Postponed
    return undefined;
  }

  var that = this;
  return when(verticesPromise, function (result) {
    var indicesAndEdges;
    if (that._skirtHeight > 0.0) {
      indicesAndEdges = TerrainProvider.getRegularGridAndSkirtIndicesAndEdgeIndices(
        result.gridWidth,
        result.gridHeight
      );
    } else {
      indicesAndEdges = TerrainProvider.getRegularGridIndicesAndEdgeIndices(
        result.gridWidth,
        result.gridHeight
      );
    }

    var vertexCountWithoutSkirts = result.gridWidth * result.gridHeight;

    // Clone complex result objects because the transfer from the web worker
    // has stripped them down to JSON-style objects.
    that._mesh = new TerrainMesh(
      center,
      new Float32Array(result.vertices),
      indicesAndEdges.indices,
      indicesAndEdges.indexCountWithoutSkirts,
      vertexCountWithoutSkirts,
      result.minimumHeight,
      result.maximumHeight,
      BoundingSphere.clone(result.boundingSphere3D),
      Cartesian3.clone(result.occludeePointInScaledSpace),
      result.numberOfAttributes,
      OrientedBoundingBox.clone(result.orientedBoundingBox),
      TerrainEncoding.clone(result.encoding),
      exaggeration,
      indicesAndEdges.westIndicesSouthToNorth,
      indicesAndEdges.southIndicesEastToWest,
      indicesAndEdges.eastIndicesNorthToSouth,
      indicesAndEdges.northIndicesWestToEast
    );

    // Free memory received from server after mesh is created.
    that._buffer = undefined;
    return that._mesh;
  });
};

/**
 * @param {Object} options Object with the following properties:
 * @param {TilingScheme} options.tilingScheme The tiling scheme to which this tile belongs.
 * @param {Number} options.x The X coordinate of the tile for which to create the terrain data.
 * @param {Number} options.y The Y coordinate of the tile for which to create the terrain data.
 * @param {Number} options.level The level of the tile for which to create the terrain data.
 * @param {Number} [options.exaggeration=1.0] The scale used to exaggerate the terrain.
 *
 * @private
 */
HeightmapTerrainData.prototype._createMeshSync = function (options) {
  //>>includeStart('debug', pragmas.debug);
  Check.typeOf.object("options.tilingScheme", options.tilingScheme);
  Check.typeOf.number("options.x", options.x);
  Check.typeOf.number("options.y", options.y);
  Check.typeOf.number("options.level", options.level);
  //>>includeEnd('debug');

  var tilingScheme = options.tilingScheme;
  var x = options.x;
  var y = options.y;
  var level = options.level;
  var exaggeration = defaultValue(options.exaggeration, 1.0);

  var ellipsoid = tilingScheme.ellipsoid;
  var nativeRectangle = tilingScheme.tileXYToNativeRectangle(x, y, level);
  var rectangle = tilingScheme.tileXYToRectangle(x, y, level);

  // Compute the center of the tile for RTC rendering.
  var center = ellipsoid.cartographicToCartesian(Rectangle.center(rectangle));

  var structure = this._structure;

  var levelZeroMaxError = TerrainProvider.getEstimatedLevelZeroGeometricErrorForAHeightmap(
    ellipsoid,
    this._width,
    tilingScheme.getNumberOfXTilesAtLevel(0)
  );
  var thisLevelMaxError = levelZeroMaxError / (1 << level);
  this._skirtHeight = Math.min(thisLevelMaxError * 4.0, 1000.0);

  var result = HeightmapTessellator.computeVertices({
    heightmap: this._buffer,
    structure: structure,
    includeWebMercatorT: true,
    width: this._width,
    height: this._height,
    nativeRectangle: nativeRectangle,
    rectangle: rectangle,
    relativeToCenter: center,
    ellipsoid: ellipsoid,
    skirtHeight: this._skirtHeight,
    isGeographic: tilingScheme.projection instanceof GeographicProjection,
    exaggeration: exaggeration,
  });

  // Free memory received from server after mesh is created.
  this._buffer = undefined;

  var indicesAndEdges;
  if (this._skirtHeight > 0.0) {
    indicesAndEdges = TerrainProvider.getRegularGridAndSkirtIndicesAndEdgeIndices(
      this._width,
      this._height
    );
  } else {
    indicesAndEdges = TerrainProvider.getRegularGridIndicesAndEdgeIndices(
      this._width,
      this._height
    );
  }

  var vertexCountWithoutSkirts = result.gridWidth * result.gridHeight;

  // No need to clone here (as we do in the async version) because the result
  // is not coming from a web worker.
  return new TerrainMesh(
    center,
    result.vertices,
    indicesAndEdges.indices,
    indicesAndEdges.indexCountWithoutSkirts,
    vertexCountWithoutSkirts,
    result.minimumHeight,
    result.maximumHeight,
    result.boundingSphere3D,
    result.occludeePointInScaledSpace,
    result.encoding.getStride(),
    result.orientedBoundingBox,
    result.encoding,
    exaggeration,
    indicesAndEdges.westIndicesSouthToNorth,
    indicesAndEdges.southIndicesEastToWest,
    indicesAndEdges.eastIndicesNorthToSouth,
    indicesAndEdges.northIndicesWestToEast
  );
};

/**
 * Computes the terrain height at a specified longitude and latitude.
 *
 * @param {Rectangle} rectangle The rectangle covered by this terrain data.
 * @param {Number} longitude The longitude in radians.
 * @param {Number} latitude The latitude in radians.
 * @returns {Number} The terrain height at the specified position.  If the position
 *          is outside the rectangle, this method will extrapolate the height, which is likely to be wildly
 *          incorrect for positions far outside the rectangle.
 */
HeightmapTerrainData.prototype.interpolateHeight = function (
  rectangle,
  longitude,
  latitude
) {
  var width = this._width;
  var height = this._height;

  var structure = this._structure;
  var stride = structure.stride;
  var elementsPerHeight = structure.elementsPerHeight;
  var elementMultiplier = structure.elementMultiplier;
  var isBigEndian = structure.isBigEndian;
  var heightOffset = structure.heightOffset;
  var heightScale = structure.heightScale;

  var isMeshCreated = defined(this._mesh);
  var isLERCEncoding = this._encoding === HeightmapEncoding.LERC;
  var isInterpolationImpossible = !isMeshCreated && isLERCEncoding;
  if (isInterpolationImpossible) {
    // We can't interpolate using the buffer because it's LERC encoded
    //  so please call createMesh() first and interpolate using the mesh;
    //  as mesh creation will decode the LERC buffer
    return undefined;
  }

  var heightSample;
  if (isMeshCreated) {
    var buffer = this._mesh.vertices;
    var encoding = this._mesh.encoding;
    var exaggeration = this._mesh.exaggeration;
    heightSample = interpolateMeshHeight(
      buffer,
      encoding,
      heightOffset,
      heightScale,
      rectangle,
      width,
      height,
      longitude,
      latitude,
      exaggeration
    );
  } else {
    heightSample = interpolateHeight(
      this._buffer,
      elementsPerHeight,
      elementMultiplier,
      stride,
      isBigEndian,
      rectangle,
      width,
      height,
      longitude,
      latitude
    );
    heightSample = heightSample * heightScale + heightOffset;
  }

  return heightSample;
};

/**
 * Upsamples this terrain data for use by a descendant tile.  The resulting instance will contain a subset of the
 * height samples in this instance, interpolated if necessary.
 *
 * @param {TilingScheme} tilingScheme The tiling scheme of this terrain data.
 * @param {Number} thisX The X coordinate of this tile in the tiling scheme.
 * @param {Number} thisY The Y coordinate of this tile in the tiling scheme.
 * @param {Number} thisLevel The level of this tile in the tiling scheme.
 * @param {Number} descendantX The X coordinate within the tiling scheme of the descendant tile for which we are upsampling.
 * @param {Number} descendantY The Y coordinate within the tiling scheme of the descendant tile for which we are upsampling.
 * @param {Number} descendantLevel The level within the tiling scheme of the descendant tile for which we are upsampling.
 * @returns {Promise.<HeightmapTerrainData>|undefined} A promise for upsampled heightmap terrain data for the descendant tile,
 *          or undefined if too many asynchronous upsample operations are in progress and the request has been
 *          deferred.
 */
HeightmapTerrainData.prototype.upsample = function (
  tilingScheme,
  thisX,
  thisY,
  thisLevel,
  descendantX,
  descendantY,
  descendantLevel
) {
  //>>includeStart('debug', pragmas.debug);
  if (!defined(tilingScheme)) {
    throw new DeveloperError("tilingScheme is required.");
  }
  if (!defined(thisX)) {
    throw new DeveloperError("thisX is required.");
  }
  if (!defined(thisY)) {
    throw new DeveloperError("thisY is required.");
  }
  if (!defined(thisLevel)) {
    throw new DeveloperError("thisLevel is required.");
  }
  if (!defined(descendantX)) {
    throw new DeveloperError("descendantX is required.");
  }
  if (!defined(descendantY)) {
    throw new DeveloperError("descendantY is required.");
  }
  if (!defined(descendantLevel)) {
    throw new DeveloperError("descendantLevel is required.");
  }
  var levelDifference = descendantLevel - thisLevel;
  if (levelDifference > 1) {
    throw new DeveloperError(
      "Upsampling through more than one level at a time is not currently supported."
    );
  }
  //>>includeEnd('debug');

  var meshData = this._mesh;
  if (!defined(meshData)) {
    return undefined;
  }

  var width = this._width;
  var height = this._height;
  var structure = this._structure;
  var stride = structure.stride;

  var heights = new this._bufferType(width * height * stride);

  var buffer = meshData.vertices;
  var encoding = meshData.encoding;

  // PERFORMANCE_IDEA: don't recompute these rectangles - the caller already knows them.
  var sourceRectangle = tilingScheme.tileXYToRectangle(thisX, thisY, thisLevel);
  var destinationRectangle = tilingScheme.tileXYToRectangle(
    descendantX,
    descendantY,
    descendantLevel
  );

  var heightOffset = structure.heightOffset;
  var heightScale = structure.heightScale;
  var exaggeration = meshData.exaggeration;

  var elementsPerHeight = structure.elementsPerHeight;
  var elementMultiplier = structure.elementMultiplier;
  var isBigEndian = structure.isBigEndian;

  var divisor = Math.pow(elementMultiplier, elementsPerHeight - 1);

  for (var j = 0; j < height; ++j) {
    var latitude = CesiumMath.lerp(
      destinationRectangle.north,
      destinationRectangle.south,
      j / (height - 1)
    );
    for (var i = 0; i < width; ++i) {
      var longitude = CesiumMath.lerp(
        destinationRectangle.west,
        destinationRectangle.east,
        i / (width - 1)
      );
      var heightSample = interpolateMeshHeight(
        buffer,
        encoding,
        heightOffset,
        heightScale,
        sourceRectangle,
        width,
        height,
        longitude,
        latitude,
        exaggeration
      );

      // Use conditionals here instead of Math.min and Math.max so that an undefined
      // lowestEncodedHeight or highestEncodedHeight has no effect.
      heightSample =
        heightSample < structure.lowestEncodedHeight
          ? structure.lowestEncodedHeight
          : heightSample;
      heightSample =
        heightSample > structure.highestEncodedHeight
          ? structure.highestEncodedHeight
          : heightSample;

      setHeight(
        heights,
        elementsPerHeight,
        elementMultiplier,
        divisor,
        stride,
        isBigEndian,
        j * width + i,
        heightSample
      );
    }
  }

  return new HeightmapTerrainData({
    buffer: heights,
    width: width,
    height: height,
    childTileMask: 0,
    structure: this._structure,
    createdByUpsampling: true,
  });
};

/**
 * Determines if a given child tile is available, based on the
 * {@link HeightmapTerrainData.childTileMask}.  The given child tile coordinates are assumed
 * to be one of the four children of this tile.  If non-child tile coordinates are
 * given, the availability of the southeast child tile is returned.
 *
 * @param {Number} thisX The tile X coordinate of this (the parent) tile.
 * @param {Number} thisY The tile Y coordinate of this (the parent) tile.
 * @param {Number} childX The tile X coordinate of the child tile to check for availability.
 * @param {Number} childY The tile Y coordinate of the child tile to check for availability.
 * @returns {Boolean} True if the child tile is available; otherwise, false.
 */
HeightmapTerrainData.prototype.isChildAvailable = function (
  thisX,
  thisY,
  childX,
  childY
) {
  //>>includeStart('debug', pragmas.debug);
  if (!defined(thisX)) {
    throw new DeveloperError("thisX is required.");
  }
  if (!defined(thisY)) {
    throw new DeveloperError("thisY is required.");
  }
  if (!defined(childX)) {
    throw new DeveloperError("childX is required.");
  }
  if (!defined(childY)) {
    throw new DeveloperError("childY is required.");
  }
  //>>includeEnd('debug');

  var bitNumber = 2; // northwest child
  if (childX !== thisX * 2) {
    ++bitNumber; // east child
  }
  if (childY !== thisY * 2) {
    bitNumber -= 2; // south child
  }

  return (this._childTileMask & (1 << bitNumber)) !== 0;
};

/**
 * Gets a value indicating whether or not this terrain data was created by upsampling lower resolution
 * terrain data.  If this value is false, the data was obtained from some other source, such
 * as by downloading it from a remote server.  This method should return true for instances
 * returned from a call to {@link HeightmapTerrainData#upsample}.
 *
 * @returns {Boolean} True if this instance was created by upsampling; otherwise, false.
 */
HeightmapTerrainData.prototype.wasCreatedByUpsampling = function () {
  return this._createdByUpsampling;
};

function interpolateHeight(
  sourceHeights,
  elementsPerHeight,
  elementMultiplier,
  stride,
  isBigEndian,
  sourceRectangle,
  width,
  height,
  longitude,
  latitude
) {
  var fromWest =
    ((longitude - sourceRectangle.west) * (width - 1)) /
    (sourceRectangle.east - sourceRectangle.west);
  var fromSouth =
    ((latitude - sourceRectangle.south) * (height - 1)) /
    (sourceRectangle.north - sourceRectangle.south);

  var westInteger = fromWest | 0;
  var eastInteger = westInteger + 1;
  if (eastInteger >= width) {
    eastInteger = width - 1;
    westInteger = width - 2;
  }

  var southInteger = fromSouth | 0;
  var northInteger = southInteger + 1;
  if (northInteger >= height) {
    northInteger = height - 1;
    southInteger = height - 2;
  }

  var dx = fromWest - westInteger;
  var dy = fromSouth - southInteger;

  southInteger = height - 1 - southInteger;
  northInteger = height - 1 - northInteger;

  var southwestHeight = getHeight(
    sourceHeights,
    elementsPerHeight,
    elementMultiplier,
    stride,
    isBigEndian,
    southInteger * width + westInteger
  );
  var southeastHeight = getHeight(
    sourceHeights,
    elementsPerHeight,
    elementMultiplier,
    stride,
    isBigEndian,
    southInteger * width + eastInteger
  );
  var northwestHeight = getHeight(
    sourceHeights,
    elementsPerHeight,
    elementMultiplier,
    stride,
    isBigEndian,
    northInteger * width + westInteger
  );
  var northeastHeight = getHeight(
    sourceHeights,
    elementsPerHeight,
    elementMultiplier,
    stride,
    isBigEndian,
    northInteger * width + eastInteger
  );

  return triangleInterpolateHeight(
    dx,
    dy,
    southwestHeight,
    southeastHeight,
    northwestHeight,
    northeastHeight
  );
}

function interpolateMeshHeight(
  buffer,
  encoding,
  heightOffset,
  heightScale,
  sourceRectangle,
  width,
  height,
  longitude,
  latitude,
  exaggeration
) {
  // returns a height encoded according to the structure's heightScale and heightOffset.
  var fromWest =
    ((longitude - sourceRectangle.west) * (width - 1)) /
    (sourceRectangle.east - sourceRectangle.west);
  var fromSouth =
    ((latitude - sourceRectangle.south) * (height - 1)) /
    (sourceRectangle.north - sourceRectangle.south);

  var westInteger = fromWest | 0;
  var eastInteger = westInteger + 1;
  if (eastInteger >= width) {
    eastInteger = width - 1;
    westInteger = width - 2;
  }

  var southInteger = fromSouth | 0;
  var northInteger = southInteger + 1;
  if (northInteger >= height) {
    northInteger = height - 1;
    southInteger = height - 2;
  }

  var dx = fromWest - westInteger;
  var dy = fromSouth - southInteger;

  southInteger = height - 1 - southInteger;
  northInteger = height - 1 - northInteger;

  var southwestHeight =
    (encoding.decodeHeight(buffer, southInteger * width + westInteger) /
      exaggeration -
      heightOffset) /
    heightScale;
  var southeastHeight =
    (encoding.decodeHeight(buffer, southInteger * width + eastInteger) /
      exaggeration -
      heightOffset) /
    heightScale;
  var northwestHeight =
    (encoding.decodeHeight(buffer, northInteger * width + westInteger) /
      exaggeration -
      heightOffset) /
    heightScale;
  var northeastHeight =
    (encoding.decodeHeight(buffer, northInteger * width + eastInteger) /
      exaggeration -
      heightOffset) /
    heightScale;

  return triangleInterpolateHeight(
    dx,
    dy,
    southwestHeight,
    southeastHeight,
    northwestHeight,
    northeastHeight
  );
}

function triangleInterpolateHeight(
  dX,
  dY,
  southwestHeight,
  southeastHeight,
  northwestHeight,
  northeastHeight
) {
  // The HeightmapTessellator bisects the quad from southwest to northeast.
  if (dY < dX) {
    // Lower right triangle
    return (
      southwestHeight +
      dX * (southeastHeight - southwestHeight) +
      dY * (northeastHeight - southeastHeight)
    );
  }

  // Upper left triangle
  return (
    southwestHeight +
    dX * (northeastHeight - northwestHeight) +
    dY * (northwestHeight - southwestHeight)
  );
}

function getHeight(
  heights,
  elementsPerHeight,
  elementMultiplier,
  stride,
  isBigEndian,
  index
) {
  index *= stride;

  var height = 0;
  var i;

  if (isBigEndian) {
    for (i = 0; i < elementsPerHeight; ++i) {
      height = height * elementMultiplier + heights[index + i];
    }
  } else {
    for (i = elementsPerHeight - 1; i >= 0; --i) {
      height = height * elementMultiplier + heights[index + i];
    }
  }

  return height;
}

function setHeight(
  heights,
  elementsPerHeight,
  elementMultiplier,
  divisor,
  stride,
  isBigEndian,
  index,
  height
) {
  index *= stride;

  var i;
  if (isBigEndian) {
    for (i = 0; i < elementsPerHeight - 1; ++i) {
      heights[index + i] = (height / divisor) | 0;
      height -= heights[index + i] * divisor;
      divisor /= elementMultiplier;
    }
  } else {
    for (i = elementsPerHeight - 1; i > 0; --i) {
      heights[index + i] = (height / divisor) | 0;
      height -= heights[index + i] * divisor;
      divisor /= elementMultiplier;
    }
  }
  heights[index + i] = height;
}
export default HeightmapTerrainData;