Low Frame Rate Panning

Serengeti (Rhino WIP)
1

Apologies if someone has mentioned this already, my search turned up nothing

In the most recent WIP build the frame rate while panning seems normal at first but drops significantly after about half a second, and remains that way until i release the RMB.

edit: I should note that when i first ran the WIP it prompted me to update my NVIDIA driver, which I did. Will upload a screencap if needed. Video Info:

NVIDIA Corporation
Quadro FX 4800/PCIe/SSE2
OpenGL: 3.3.0
Render version: 2.0
Shading Language: 3.30 NVIDIA via Cg compiler
Driver Date: 8-4-2014
Driver Version: 9.18.13.4066
Maximum Texture size: 8192 x 8192
Z-buffer depth: 24 bits
Maximum Viewport size: 8192 x 8192
Total video memory: 1536 MB

2

Update: After more playing around, the problem seems to be limited to the perspective viewport, and only when it is maximized. Most display modes (with the possible exception of pen and artistic) are affected