It seems the new vDOS has a problem with programs designed to use VGA standard mode $12: 640x480, 16 colors. In the vDOS version of 1 March 2020 my program looks like this:
In the new version (downloaded today) I get this:
For your convenience I added a small program for testing. It switches to graphics mode and shows an on screen message. In the old versions this worked perfectly. In the new version it does not. I hope this helps you to solve this.
Version 2021.05.01 abstracts the VGA hardware more than 2020.03.01. vDos previously programmed/initialized VGA registers, then the display mode was determined based on those registers. Quite a roundabout, so that method is abandoned.
Your program heavily uses the VGA registers. Although I reconstructed a lot of the previous logic, that didn’t bring the desired result. Could be some VGA register still not initialized correctly, or just not supported anymore while your program depends on that.
Until now you’re the only one with this problem. More important, vDos is mainly meant for text based applications and the new and old logic differ a real lot. So sorry, but I have to let this go (for now?). You’ll have to resort to version 2020.03.01 for graphic based programs.
Sorry to have to say this, but Ronald is not the only one with this problem. I'm using Word 6.0 for DOS. Text mode works, Graphics mode also, but the full page graphic preview does not work any more (it shows just black screen). It worked in 2020.03.01 though.
As said, VGA hardware is abstracted more. I even once was about to drop VGA graphic support altogether, that was only stopped at the very last moment by Edward Mendelson for WP’s print preview. I have no interest whatsoever in graphical content, the only consideration is WP’s print preview still working. Sorry for that.