clb wrote on 2024-02-10, 23:09:

Hi, […]
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Hi,

I am diagnosing behavior of some DOS games, and I realize that I'd like to probe how these games behave if one did not have VESA support at all. Anyone know if such a tool exists?

For example, I had these games that I was looking at recently:
- Scorched Earth,
- Pinball Fantasies,
- Pinball Illusions
- Warlords 2

that all support 640x480 and some do 800x600.

I think Scorched Earth doesn't use VESA, but maybe has hardcoded INT10h SVGA mode numbers for different adapters?

The other games maybe do go via VESA?

So to be able to quickly probe games like that, it would be interesting to be able to "kill"/hide VESA support from an adapter. (also, it might be interesting to kill/override a particular SVGA mode from an adapter if there might be a tool for such a thing?)

I think I could go the route of hooking my own interrupt handlers, though I hope maybe something like this might already exist?

The VESA NOLFB might be a helpful starting point to a DIY approach NOLFB - Disables LFB enabling DOS games to fallback to VESA 1.2 modes
ASM source is included.

Thanks, super helpful! I think I can work with that, and either make the VESA info block return zeroes, or make set video mode fizzle out, or similar.

Pinball Fantasies doesn't use any SVGA modes, only tweaked VGA.

Err, yeah, you're absolutely right about Pinball Fantasies, not sure why I even wrote it on that list! (I've been staring the mode frame timings of that game for a good eight months now...)

You may try to use videocard that doesn't support any VESA modes in the BIOS. For example recently I got UM85C408AF based ISA videocard and I was surprised when realized that it supports DOS VESA modes only through dedicated TSR driver.