Ok. I think I know what's going on, but I still don't know exactly why it's going on.

It appears to be related to the video timings that DOSBox is sending to the monitor. I created a custom resolution with specific timings in Nvidia control panel for my monitor's 640x400 resolution. I have the service manual, and it specifies that it should be the same as this: http://www.tinyvga.com/vga-timing/640x400@70Hz

When I start DOSBox, it appears that the porches and/or the sync pulse length is slightly off of the standard timings and it results in some lost brightness. If I instead start DOSBox in 640x480, it gets it correct and games are instantly the same brightness as my desktop. Within DOSBox, once it's started, it appears to be displaying VGA games at the correct resolution without scaling. I've only tested a couple games so far, but it currently seems like my best option.

Anybody know why the heck this resolution thing is happening?

DOSBox has no control over that, it just tells windows what resolution it wants the display to be. The display driver decides what specific timings will be used.

Can you try something other than DOSBox at that custom resolution and see if you have the same issue ?

Does your video card actually have VGA output (either directly or through a passive DVI-I to VGA converter) or are you using an active converter with a DAC ?

If you boot the machine baremetal into DOS (if hardware allows it) and launch a 320x200 VGA game (which will get output as 640x400), do you have the same issue ?

darry wrote on 2022-11-01, 10:47:

Can you try something other than DOSBox at that custom resolution and see if you have the same issue ?

The Windows 10 environment runs fine at 640x400. Some elements don't appear, for example, they delete things like the "expand" icon in the photo app, so you have to press F11 to go full screen.

Retroarch launches into it's GUI just fine, but I haven't set it up to play cores yet.

I plan to try 86Box, but haven't gotten around to it yet.

Does your video card actually have VGA output (either directly or through a passive DVI-I to VGA converter) or are you using an active converter with a DAC ?

Yes, it has a DVI-I output and I'm using a DVI-VGA cable with no circuitry inside. It outputs analog VGA.

If you boot the machine baremetal into DOS (if hardware allows it) and launch a 320x200 VGA game (which will get output as 640x400), do you have the same issue ?

I don't believe I can do so, no. It's too new a PC.

Just to reiterate, I am able to play 640x400 games now, as long as my desktop resolution is 640x480 and I use OpenGL. All I have to do is set DOSBox's fullscreen res to 640x400 and it displays properly on the CRT.

The weird thing that persists is that I can't switch to another output method, and if my desktop resolution is 640x400, everything in DOSBox is super dark.

jmarsh wrote on 2022-11-01, 08:51:

DOSBox has no control over that, it just tells windows what resolution it wants the display to be. The display driver decides what specific timings will be used.

Thanks. I followed up on this, and it was indeed my Nvidia drivers creating havoc. In order to get things to work properly, I had to download Custom Resolution Utility and create the correct resolutions with their respective timings, and then enable them in the Nvidia control panel. It was not fun. 🤣

But now I can use all output methods with similar results. I'm not sure why OpenGL was working when it somehow shouldn't have been, but I guess maybe SDL talks to OpenGL on a hardware level, idk.