This way, it can be focused with the render window behind it, instead of having the main window show up and cover the render window. This is useful for adjusting the object range, among other things.
If the number of objects varied, this would result in either missing objects on some frames, or too many objects on some frames; the latter case could cause crashes. Since it used the current frame to get the count, if the FIFO is started before the FIFO analyzer is opened, then the current frame is effectively random, making it hard to reproduce consistently.
This issue has existed since the FIFO analyzer was implemented for Qt.
The 'zero frames in the range' check can be removed because now there is always at least 1 frame; of course that might be the same frame over and over again, but that's still useful for e.g. Free Look (and the 1 frame repeating effect already occurred when frame count was exclusive).
A single object can be selected instead of 2 (it was already inclusive internally), and the maximum value is the highest number of objects in any frame (minus 1) to reduce jank when multiple frames are being played back.
Now that this is only called when playback actually starts (and not on unpausing), this change makes the experience a bit better (no more missing objects from not having reset the from object after changing FIFOs).
Pokechu22