Limit CesiumJS Camera Tilt

limit-cesiumjs-camera-tilt.js

const viewer = new Cesium.Viewer("cesiumContainer");
const globe = viewer.scene.globe;
const camera = viewer.scene.camera;

const scratchNormal = new Cesium.Cartesian3();
const previousPosition = new Cesium.Cartesian3();
const previousDirection = new Cesium.Cartesian3();
const previousUp = new Cesium.Cartesian3();
const previousRight = new Cesium.Cartesian3();

viewer.scene.postUpdate.addEventListener(function() {
  const normal = globe.ellipsoid.geodeticSurfaceNormal(
    camera.position,
    scratchNormal
  );

  const dotProduct = Cesium.Cartesian3.dot(camera.direction, normal);
  
  if (dotProduct >= -0.3) {
    camera.position = Cesium.Cartesian3.clone(previousPosition, camera.position);
    camera.direction = Cesium.Cartesian3.clone(previousDirection, camera.direction);
    camera.up = Cesium.Cartesian3.clone(previousUp, camera.up);
    camera.right = Cesium.Cartesian3.clone(previousRight, camera.right);
  } else {
    previousPosition = Cesium.Cartesian3.clone(camera.position, previousPosition);
    previousDirection = Cesium.Cartesian3.clone(camera.direction, previousDirection);
    previousUp = Cesium.Cartesian3.clone(camera.up, previousUp);
    previousRight = Cesium.Cartesian3.clone(camera.right, previousRight);
  }
});