It seems that just the one backdrop will cause the application to drop FPS very quickly on a big frame. Should this happen? Look at the attachement:
Using: Fusion 2.5 with latest build on Windows 7 64bit. Will provide more information if anyone needs it.
EDIT: I sent a bug report and Yves kindly answered and it solves all the issues. I feel pretty stupid now, but here is his response:
This lag seems to be due to the "Handle background collisions even out of window option". In this mode the program creates a global collision mask for the first level. Perhaps the size of the collision mask in your frame is too big (even if it uses only 2 bits per pixel, for a 30,000 x 30,000 frame it will eat 225 Mb of memory).
- either you unselect this option
- or you create an empty first layer and move the current layer above it. Layers greater than 1 have no global collision mask. Other differences with the first layer: the Paste Backdrop option works like Add Backdrop for these layers, and you can "paste" a non-obstacle backdrop to make a hole in the collision mask.