【AE表达式】根据与相机的距离，缩放3D图层

https://videolancer.net/scale-layer-depending-on-distances-from-camera

如果你把这个表达式应用到三维图层的Scale参数上，那么当你远离相机或缩放时，图层会自动增加，视觉上不会改变其大小。

cam = thisComp.activeCamera;
distance = length(sub(position, cam.position));
scale * distance / cam.zoom;