message: improve 'rounded' tube geometry
  correct normals
  circle offset
diff: */
  import { Vec3 } from '../../../../mol-math/linear-algebra';
  -import { ChunkedArray } from '../../../../mol-data/util';
  +import { cantorPairing, ChunkedArray } from '../../../../mol-data/util';
  import { MeshBuilder } from '../mesh-builder';
  const normalVector = Vec3();
  @@ -37,18 +37,20 @@ const v3unitX = Vec3.unitX;
  const caAdd3 = ChunkedArray.add3;
  const CosSinCache = new Map<number, { cos: number[], sin: number[] }>();
  -function getCosSin(radialSegments: number) {
  - if (!CosSinCache.has(radialSegments)) {
  +function getCosSin(radialSegments: number, shift: boolean) {
  + const offset = shift ? 1 : 0;
  + const hash = cantorPairing(radialSegments, offset);
  + if (!CosSinCache.has(hash)) {
  const cos: number[] = [];
  const sin: number[] = [];
  for (let j = 0; j < radialSegments; ++j) {
  - const t = 2 * Math.PI * j / radialSegments;
  + const t = (j * 2 + offset) / radialSegments * Math.PI;
  cos[j] = Math.cos(t);
  sin[j] = Math.sin(t);
  }
  - CosSinCache.set(radialSegments, { cos, sin });
  + CosSinCache.set(hash, { cos, sin });
  }
  - return CosSinCache.get(radialSegments)!;
  + return CosSinCache.get(hash)!;
  }
  export function addTube(state: MeshBuilder.State, controlPoints: ArrayLike<number>, normalVectors: ArrayLike<number>, binormalVectors: ArrayLike<number>, linearSegments: number, radialSegments: number, widthValues: ArrayLike<number>, heightValues: ArrayLike<number>, startCap: boolean, endCap: boolean, crossSection: 'elliptical' | 'rounded') {
  @@ -56,9 +58,9 @@ export function addTube(state: MeshBuilder.State, controlPoints: ArrayLike<numbe
  let vertexCount = vertices.elementCount;
  - const { cos, sin } = getCosSin(radialSegments);
  + const { cos, sin } = getCosSin(radialSegments, crossSection === 'rounded');
  - const q1 = radialSegments / 4;
  + const q1 = Math.round(radialSegments / 4);
  const q3 = q1 * 3;
  for (let i = 0; i <= linearSegments; ++i) {
  @@ -78,7 +80,13 @@ export function addTube(state: MeshBuilder.State, controlPoints: ArrayLike<numbe
  ? (j < q1 || j >= q3) ? height - width : -height + width
  : (j >= q1 && j < q3) ? -height + width : height - width;
  v3scaleAndAdd(surfacePoint, surfacePoint, u, h);
  + if (j === q1 || j === q1 - 1) {
  + add2AndScale2(normalVector, u, v, 0, 1);
  + } else if (j === q3 || j === q3 - 1) {
  + add2AndScale2(normalVector, u, v, 0, -1);
  + } else {
  add2AndScale2(normalVector, u, v, cos[j], sin[j]);
  + }
  } else {
  add3AndScale2(surfacePoint, u, v, controlPoint, height * cos[j], width * sin[j]);
  add2AndScale2(normalVector, u, v, width * cos[j], height * sin[j]);
  