What am I talking about? That big black bar at the bottom of the screen that shouldn't be there - the hi-res menu is the only one that looks fine. It was driving me nuts after a few minutes, and I figured something screwy was going on here as I never noticed this in GoG's other dosbox-using releases. I think it has to do with the aspect ratio of the used resolutions. This is the case in all of the new EA releases.

Anyway, long story short there's an easy fix for this, which I found by doing a search on the DOSBox website forum. Locate the games folder and edit the dosboxDK.cfg file with notepad or equivalent. Look for the line that says "fullresolution=original" and change it to "fullresolution=0x0". Save it, and voila! Now it properly will scale to fill the entire screen.

Note of caution to those who use a 4:3 monitor (those few of you left): this may not exactly work in your case. Why? The original resolution is greater in width - I suspect that's the reason GoG decided to have its funky configuration in the first place - so I'm not sure what happens in that case. Works beautifully on my 1080P screen though.

Edit: Out of curiosity I checked other GoG games I had that use DOSBox and it turns out they all have the same config as far as resolution is concerned, so it is indeed these games' aspect ratios that are the exception.

Quick reminder to those who don't know, pressing ALT+R will give you the high resolution graphics. A little confusing because it doesn't show under the game options anywhere.

I couldn't get mumbles fix above to work with 'fullscreen=0x0' but 'fullresolution=0x0' worked fine.

Oops. That's totally my fault. I was looking at the config file an somehow confused myself into writing the wrong thing for the second part. You're absolutely right, "fullresolution=0x0" is what needs to be put there instead.

Didn't work for me on Linux, so I set the fullresolution parameter to my native resolution (1680x1050) and it works beautifully. But the game is somewhat (well, very) sluggish... any DOSBox gurus out there that can tell me how to increase performance? :-)

Turn off any kind of scaling (normal2x, hq2x, etc.), and experiement with the different rendering methods (OpenGL, DDraw, Surface, etc.)

Yeah I did this as well, looks great.

Thanks for the tip!
Worked as a charm :)

I'm not sure if I'm going to the correct file, but the closest thing I found was "dosboxDK" which is a CONF file. I opened it with notepad and tried to change fullresolution=original into fullresolution=0x0, but when I tried to save it I got "cannot create the GOG.com\DungeonKeeper\dosboxDK.conf file. Make sure the path and the file name are correct."

Anyway, I tried it on wordpad with similar results except this time I got "access to Gog.com\DungeonKeeper\dosboxDK.conf was denied."

Is there anywhere more specific I should be looking for the correct file?

You're working with the correct file. I've attached a screenshot of my file's location for you to double check. Perhaps you can't save it due to permission problems to edit the file? Are you an admin user?

Maybe it would be worth trying Notepad++ to edit and save the file. I used that to edit mine and had no issues.

Never use wordpad to edit plain text files. You need permission to save the file, try right clicking on Notepad and running as Administrator, that or use Notepad++ as Merkaba suggests.

Thank you Mistermumbles! That fix corrected my issue!

Thanks a lot, it's exactly what I was looking for

By doing just that, I ended up with small window in the center of my 1920x1080 screen. So I also did what it says in dosboxDK.conf to do, and that is:

# fullresolution: What resolution to use for fullscreen: original or fixed size (e.g. 1024x768).
# Using your monitor's native resolution with aspect=true might give the best results.
# If you end up with small window on a large screen, try an output different from surface.

So then I changed output from surface to opengl and now I have black bars only on each side, with game in its correct aspect ratio.

Thank you gaming Jesus!