Sub window terrain blurs as main camera moves away

[qwe123]

Hi, I implemented the multi-window feature with several viewports and several other cameras,
but I found that when the sub-camera is far from the main camera, the terrain inside the sub-window gets blurry.

How to solve this problem， Thanks!

 

[qwe123]

I guess the main reason is that the camera obtained by using Game:: get() - > getcamera()  is bound to the terrain, the nearby terrain render clearly and remote terrain render coarse.