Another update.
finished the picture viewing part and polished the looks of the user interface a bit. Was not pleased with the buttons not being buttons, so modified most of that.
The new setup works with two directories. "\pictures" and "\waveforms" Was thinking about a no limits system, but with FatFs the needed code to step through pages of view items would be a pain in the bum. Going forward not that bad, but backing up a page would mean start at the beginning to find the first item of the requested page. So I reused an adapted version of the original code.
The original uses two fixed length files. One for the list with file numbers, and another for the thumbnails. I modified this to use only one file that grows with the number of saved items. It is still loaded into memory to be able to step through the thumbnail pages, which is why I limited it to the originals 1000 items per type.
The code for handling the items is for a large part the same for both types, so getting the waveform view working is not a lot of work. Need to adapt for the new sampling setup.
Once that is done, I still have to get the X-Y mode working again. Also needs to be adapted to the new sampling setup.
It will be a couple of day's before a new test release. This one will have a version number, which can be seen in one of the screen captures. Per advise of morris6 I placed it underneath the battery icon.
At some point I will setup a new github repository for just the new firmware. The reverse engineering and hacking is past tense. From now on only new code.
The picture view screen shows the file name in the bottom menu bar. As in the original this bar can be tapped away and back again by tapping outside of the button area.