<NME> zorder.ts
<BEF> /**
 * @license
 * Copyright 2019 Google Inc.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import {Uint64} from './uint64';

/**
 * Decodes a "compressed" 3-d morton index.
 *
 *
 * Decoded bit `i` of `x`, `y`, and `z` is at bit `i + min(i, yBits) + min(i, zBits)`, `i + min(i +
 * 1, xBits) + min(i, zBits)`, and `i + min(i + 1, xBits) + min(i + 1, zBits)` of `zindex`,
 * respectively, for `i` in `[0, xBits)`, `[0, yBits)`, `[0, zBits)`, respectively.
 */
export function decodeZIndexCompressed(
    zindex: Uint64, xBits: number, yBits: number, zBits: number): Uint32Array {
  const maxCoordBits = Math.max(xBits, yBits, zBits);
  let inputBit = 0;
  let inputValue = zindex.low;
  let x = 0, y = 0, z = 0;
  for (let coordBit = 0; coordBit < maxCoordBits; ++coordBit) {
    if (coordBit < xBits) {
      const bit = (inputValue >>> inputBit) & 1;
      x |= (bit << coordBit);
      if (inputBit === 31) {
        inputBit = 0;
        inputValue = zindex.high;
      } else {
        ++inputBit;
      }
    }
    if (coordBit < yBits) {
      const bit = (inputValue >>> inputBit) & 1;
      y |= (bit << coordBit);
      if (inputBit === 31) {
        inputBit = 0;
        inputValue = zindex.high;
      } else {
        ++inputBit;
      }
    }
    if (coordBit < zBits) {
      const bit = (inputValue >>> inputBit) & 1;
      z |= (bit << coordBit);
      if (inputBit === 31) {
        inputBit = 0;
        inputValue = zindex.high;
      } else {
        ++inputBit;
      }
    }
  }
  return Uint32Array.of(x, y, z);
}

export function encodeZIndexCompressed3d(
    zindex: Uint64, xBits: number, yBits: number, zBits: number, x: number, y: number,
    z: number): Uint64 {
  const maxBits = Math.max(xBits, yBits, zBits);
  let outputBit = 0;
  let outputNum = 0;
  let isHigh = false;
  function writeBit(b: number): void {
    outputNum |= (b & 1) << outputBit;
    if (++outputBit === 32) {
      zindex.low = (outputNum >>> 0);
      outputNum = 0;
      outputBit = 0;
      isHigh = true;
    }
  }
  for (let bit = 0; bit < maxBits; ++bit) {
    if (bit < xBits) {
      writeBit((x >> bit) & 1);
    }
    if (bit < yBits) {
      writeBit((y >> bit) & 1);
    }
    if (bit < zBits) {
      writeBit((z >> bit) & 1);
    }
  }
  if (isHigh) {
    zindex.high = (outputNum >>> 0);
  } else {
    zindex.high = 0;
    zindex.low = (outputNum >>> 0);
  }
  return zindex;
}

export function encodeZIndexCompressed(
    zindex: Uint64, position: TypedArray, shape: TypedArray): Uint64 {
  let outputBit = 0;
  const rank = position.length;
  let outputNum = 0;
  let isHigh = false;
  function writeBit(b: number): void {
    outputNum |= (b & 1) << outputBit;
    if (++outputBit === 32) {
      zindex.low = (outputNum >>> 0);
      outputNum = 0;
      outputBit = 0;
      isHigh = true;
    }
  }

  for (let bit = 0; bit < 32; ++bit) {
    for (let dim = 0; dim < rank; ++dim) {
      if ((shape[dim] - 1) >>> bit) {
        writeBit(position[dim] >>> bit);
      }
    }
  }
  if (isHigh) {
    zindex.high = (outputNum >>> 0);
  } else {
    zindex.high = 0;
    zindex.low = (outputNum >>> 0);
  }
  return zindex;
}

function lessMsb(a: number, b: number) {
  return a < b && a < (a ^ b);
}

/**
 * Returns `true` if `(x0, y0, z0)` occurs before `(x1, y1, z1)` in Z-curve order.
 */
export function zorder3LessThan(
    x0: number, y0: number, z0: number, x1: number, y1: number, z1: number): boolean {
  let mostSignificant0 = z0, mostSignificant1 = z1;

  if (lessMsb(mostSignificant0 ^ mostSignificant1, y0 ^ y1)) {
    mostSignificant0 = y0;
    mostSignificant1 = y1;
  }

  if (lessMsb(mostSignificant0 ^ mostSignificant1, x0 ^ x1)) {
    mostSignificant0 = x0;
    mostSignificant1 = x1;
  }

  return mostSignificant0 < mostSignificant1;
}

<MSG> refactor(mesh): refactor multiscale mesh support

This changes the octree representation to be more explicit, and eliminates the reliance on being
able to split mesh fragments down to individual base chunks; instead, mesh fragments need only be
split to the next octree level.

This also adds support for more flexible vertex position representation, which will be needed for
the precomputed multiscale mesh format to be added in a later commit.

<DFF> @@ -16,6 +16,10 @@
 
 import {Uint64} from './uint64';
 
+export function getOctreeChildIndex(x: number, y: number, z: number) {
+  return (x & 1) | ((y << 1) & 2) | ((z << 2) & 4);
+}
+
 /**
  * Decodes a "compressed" 3-d morton index.
  *

refactor(mesh): refactor multiscale mesh support