Download here

The Problem:
Sometimes JJ2(+) doesn't allow you to use fullscreen. Alt+Enter does nothing and it doesn't appear in the video options menu.

We think this is because later versions of Windows disable some DirectDraw functionality unless the special code DWM8And16BitMitigation is in a certain area of the registry. (DirectDraw is the technology that JJ2, and programs in general, use for fullscreen--I'm using them as synonyms here.)

This experimental build adds DWM8And16BitMitigation to the registry when you run it.

Caveats:

• The string is added to the registry the first time you run JJ2+. Therefore, it won't work the first time, DirectDraw will still be unavailable. It should only start being available the second time you run JJ2+, and then continue to be available every time thereafter.
• This needs to be set in the registry for every different path to Jazz2.exe you have. So if you have multiple copies of JJ2+ installed in different folders, you'll need to do this for each folder.

How to test this:
Download this ZIP and extract the plus.dll file into your JJ2+ folder. You may make a backup of the original plus.dll first, if you want.

• Try running JJ2 many times in a row, to make sure that the fix doesn't stop working at some point.
• Try renaming the folder to see if the fix can catch up to the new name/s. (Again, it may only start working the second time you run JJ2+ in each different folder name.)
• Try other things that we haven't thought of!

Next Steps
If we hear that this build successfully fixes the problem for affected players, we will release it as an update to JJ2+, so everyone gets the fix, not just people looking at this particular forum thread.

If not, we'll go back to researching the problem.

Works for me, but with some oddities. Playing on Windows 10.

- Confirmed that a fresh install Jazz2Plus folder lfrom GOG acks directdraw fullscreen as mentioned in this forum post

- Subsequent launches works as described above. Small note that GOG installs with HIGHDPIAWARE registry already in there and this new plus.dll gives it a second time, without checking if it's already present. So it ends up with the line "DWM8And16BitMitigation HIGHDPIAWARE HIGHDPIAWARE".

-Renaming the folder into different folders, or making a new folder and copying all files into it interestingly enough does never make directdraw dissapear. When launching and refreshing the registry DW8And16Bitmitigation is added to the new folder and it works immediately on the FIRST launch and subsequent launches.

-Thus the only way of removing directdraw (for one launch) I could find is if I remove the registry manually.

Sounds like it works better than expected, then; off to a good start!

The double HIGHDPIAWARE should totally be fixable.