I think you should try different scaler types... 😉

Scalers shouldn't matter. More likely you need to change the output method in the dosbox.conf file.

When I switch to fullscreen mode, I get a small picture with a black border around it- in other words, the picture stays the sam […]
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When I switch to fullscreen mode, I get a small picture with a black border around it- in other words, the picture stays the same fixed size, while the rest of the 'full' screen is blank. I've messed around with the config file quite a bit, and tried previous versions of dosbox, all to no avail. What do I do to get a true full screen?

you answered: Scalers shouldn't matter. More likely you need to change the output method in the dosbox.conf file.

i have the same problem, what should i do ??? and what do i need to change in the output= ??????

i cant speak english well.
hope you understand

see ya

Try these settings in dosbox.conf:

1[sdl]
2output=overlay
3windowresolution=1024x768

Now run DOSBox in windowed-mode and you should get a nice big window. Adjust the 1024x768 to match your actual full screen size, and it will be just like fullscreen-mode. (I hope)

Isn't there a way to do the scaling in full-screen mode? I have this same problem and you gave me similar advise, but I'd like to get rid of the title bar and taskbar while playing a game. Also, it seems to keep aspect ratio, even when I have aspect=false.

I'd love to just have fullscreen scaled to the whole screen.

fullresolution ?

Full resolution does not scale, but puts the 640x400 resolution unscaled on the screen, resulting in black bars on top and bottom. That's the problem. 🙁

Try different output= settings then, and update/downgrade your
graphics card drivers.

I know I'm hijacking the thread a bit, but I'm having the same problem, anyway. 😉 I've tried several outputs: overlay, opengl, ddraw... to no avail. I could try upgrading my video drivers, but they are pretty recent and I have little faith that it will help...

But you're telling me that it should just scale to the right resolution if I put 640x480 or my desktop resolution as fullresolution? Even knowing that would help, because it'd mean that something is not right at my side.

I had the same issue playing dark forces fullscreen in dosbox, and fixed it by using:
fullscreen=true
fullresolution=640x480
output=surface
I hope this helps you.

Nope, none of the outputs make any difference. The result is always the same, which leads me to believe that DOSBox isn't doing something that it should be doing according to the config.

By the way, the game in question is Toonstruck. Maybe it's just the game giving trouble?