How to increase the frame rate when pitch of viewpoint is above -20?
I found that, in osgearth, frame rate is significantly affected by the pitch of view. When the pitching angle is near -90 degrees, the frame rate could be about 60. And when the pitch rises to -20, the frame rate would fall below 20.
Why did this happen? And How to increase the frame rate when the pitching angle is above -20?