v4.30 win xp sp3

The thumbnail pane has serious performance and ui issues when there are a large number of images in a directory, say more than a few hundred.

Problem 1. Any action which causes a refresh of the thumbnail pane starts at the first file in the directory and continues in sequence until all thumbnails are refreshed. This can take a VERY long time.

Feature request 1. Change the order of thumbnail refresh as follows:
1. refresh any thumbnails which are currently selected and currently visible.
2. refresh all remaining thumbnails currently visible
3. refresh remaining thumbnails in background.
4. if user scrolls window, changing what is visible, modify the refresh queue and do 1. and 2. again as needed before continuing with 4.
Feature request 2. Thumbnail refresh is slower than many other programs. Consider some speedup, such as reading image files by strides.

Problem 2. User attempting to move thumbnail panel window to include a desired thumbnail range fails if thumbnails are being refreshed: user is soon ignored and visibility returns either to initial segment or wherever the thumbnail refresher is currently working.

Feature request 3. Get rid of the annoying behavior. Do not move viewport except when user does it through the ui.