[ptx] Sluggish behaviour of the preview window

[Ulf Wilhelmson]

Hi.

I have seen a very sluggish behavior of the preview window when dragging the 
fov-sliders. The remapping of the images do not seam to be very efficient and 
thus takes some time to perform.

This leads to another rather-annoying effect. During the remapping the program 
seams to be blind for mouse button actions and often miss the release of the 
button. The problem naturally increases with the number of images and possible 
also the original image size, this I'm not sure about though.
 
When the button release is missed the remapping starts over again when the 
mouse is moved outside the image area. I'm running the OSX versions and do not 
know whether it is a mac-only issue.

May I suggest two possible solutions:

It seams like the preview are using versions of all original images separately 
and preform a remapping every time on each of them, regardless if it is a 
result of a re-optimization, a change of projection or 
a change of fov. 

If all shape-changing operations instead created a common image for previewing, 
this image might be more efficient for rescaling when changing the fov. 

An even faster alternative might be to use the outline of the combined image 
during the slider operation to show the resulting edge, and performing the 
remapping after mouse button release is detected.

Sorry for the wordy post.  
I also hope I'm not annoying anybody by suggestions in an area I have little 
knowledge about.

Ulf