by Axel on Mon May 21, 2012 12:45 pm
FastPictureViewer scans the image folder (and all its subfolders, if enabled) immediately upon startup. Instead of having the user wait for the folder scan to complete before displaying the first image, it starts displaying as soon as a few files are discovered.
The file system returns files in immaterial order (they are not sorted in any meaningful way) and the program inserts the files at their actual place in its internal list, relative to the sort order in effect (name or time), as they are found.
The folder scan is very quick, in the order of 1,000-2,000 files per second on a fast computer. Now imagine that file 00000000.JPG (say it's the first overall in alphabetic order) is the last file on your hard drive, and say that you open said hard drive in FPV Pro.
Say there are 2,000 images on that drive and that FPV on your particular computer scans folders at 1,000 files per second. It will take a couple of seconds before file 00000000.JPG is discovered and FPV will have displayed something long before that moment.
One can say that the program display a partially ordered set of images during the initial discovery. The order certanily is not random, but you can think that there are "holes" in the list, that gets filled in as files are discovered. Only after all files have been found the order becomes total.
The folder scan and file discovery usually only takes a fraction of a second, unless the folder/subfolders contain many files or if the computer is slow. The program displays a "+" indicator next to the image count at the bottom-right while the file discovery is still active in the background.
Sorting on EXIF date or GPS time stamp makes the discovery slower than when sorting on file name or file date.
When starting the program on a particular file (e.g. by double-clicking the file in Explorer if FPV is set as the default viewer for that format) the program opens and displays that file immediately, and scans its siblings in parallel.
As soon as the scan is complete (the "+" sign is gone) you'll find that the file you clicked on it at its place within the whole list, according to the sort mode in effect within FPV.
If you open a folder and immediately click on the "Next" button, right after an image was displayed and before the folder scan is complete, the program will immediately move to the next image among those already discovered at the instant you clicked the button.
In some cases this may not be the same image as the one it would move to if you had clicked "Next" a fraction of a second later, after the discovery is complete and all found files are at their logical place in the ordered list.
Some programs maintains their own database of files (a "catalog") and can display files in various orders without waiting for discovery. On the other hand, FPV just displays what's in your folders and is never out of sync with your files, and there is no catalog to create, maintain, reindex, rebuild, repair or backup.