Entity始终面向相机

/*
 *直接调用这个方法即可
 *entityPosition Cartesian3 类型
 */
function ToFaceCamera(entity, entityPosition) {
    viewer.scene.postUpdate.addEventListener(function () {
      let cameraPosition = viewer.camera.position;
      let rotation=changeOrientation(entityPosition,cameraPosition);
      entity.orientation =rotation;
    })

  }
function changeOrientation(posA,posB) {
    
    let m = getModelMatrix(posA, posB);
    let hpr = getHeadingPitchRoll(m);
    hpr.pitch=0;
    hpr.roll=0;
    let orientation = Cesium.Transforms.headingPitchRollQuaternion(
        posA,
        hpr
    );

    return orientation;
}

function getModelMatrix(pointA, pointB) {
    //向量AB
    const vector2 = Cesium.Cartesian3.subtract(
        pointB,
        pointA,
        new Cesium.Cartesian3()
    );
    //归一化
    const normal = Cesium.Cartesian3.normalize(vector2, new Cesium.Cartesian3());
    //旋转矩阵 rotationMatrixFromPositionVelocity源码中有，并未出现在cesiumAPI中
    const rotationMatrix3 = Cesium.Transforms.rotationMatrixFromPositionVelocity(
        pointA,
        normal,
        Cesium.Ellipsoid.WGS84
    );
    const modelMatrix4 = Cesium.Matrix4.fromRotationTranslation(
        rotationMatrix3,
        pointA
    );
    return modelMatrix4;
}

function getHeadingPitchRoll(m) {
    var m1 = Cesium.Transforms.eastNorthUpToFixedFrame(
        Cesium.Matrix4.getTranslation(m, new Cesium.Cartesian3()),
        Cesium.Ellipsoid.WGS84,
        new Cesium.Matrix4()
    );
    // 矩阵相除
    var m3 = Cesium.Matrix4.multiply(
        Cesium.Matrix4.inverse(m1, new Cesium.Matrix4()),
        m,
        new Cesium.Matrix4()
    );
    // 得到旋转矩阵
    var mat3 = Cesium.Matrix4.getMatrix3(m3, new Cesium.Matrix3());
    // 计算四元数
    var q = Cesium.Quaternion.fromRotationMatrix(mat3);
    // 计算旋转角(弧度)
    var hpr = Cesium.HeadingPitchRoll.fromQuaternion(q);
    return hpr;
}