TheOligopolist wrote on 2024-04-01, 23:17:

This could be a false memory of course, but I'm wondering if some CGA cards would cause a game to run using a different set of colours or something (if any computer manufacturer would be using oddball components, I think it would be AMSTRAD).

No no, I don't think it's a false memory.
Real CGA had two official palettes, with two intensity levels each.
On top of that, there was an inofficial third palette, with two intensity levels, again.
Composite CGA also was an option on NTSC monitors.

BIOS wise, the two palettes were being supported no problem. Many CGA games wrote directly to the registers of the MC6845 graphics chip, though and didn't use PC BIOS.

And here's the catch: Any CGA imitation circuit or EGA or VGA cards can support the two palettes if the game uses BIOS calls.

In fact, CGA is the only graphics hardware being supported by the PC BIOS.

That's why it was such a big deal back then, it was the ideal fall-back. CGA routines always worked.
Even Hercules users could run CGA software through a color graphics emulator (SIMCGA).

Games that use the BIOS method are Pharaoh's Tomb and Monuments on Mars.
They support the green/red palette on both CGA and EGA/VGA PCs.

_
So it might be possible that your game was either being patchedto use a little BIOS call
to set palette, that it was an Amstrad version or that it simply was a newer revision with better hardware support.

Another explanation is that your graphics chip back then had some partial CGA register support or had an Amstrad-specific support.

Maybe DOSBox doesn't emulate this aspect properly, I don't know.

You can try DOSBox-X, PCem/86Box or faithful PC/XT emulators like MartyPC if you have doubts.

_
This wasn't being too unusual. Many third-party EGA and VGA cards had a mode utility to "lock" the card into a specific graphics hardware mode.

There were entries for such things as CGA, Hercules, EGA, Olivetti or 132 columns text mode..

By selecting "CGA" in that utility, for example, programs would merely detect a plain CGA card.
The blocky CGA text mode font (8x8) would likely be available, too, making old text-mode GUIs (or rather, "TUIs") look fine (spacing would be even)

Some weird card I've seen on YouTube did support CGA register compatibility even without using mode utility.

That "feature" was convenient, but also a violation against the claim to be 100% VGA compatible.

Because, aiming for full VGA compatibility also includes all of the shortcomings of IBM VGA (imperfect CGA).

Not sure if this is the same thing as with this game, but if you set DOSBox to machine=cga and play PopCorn, it will use a CGA palette with the red colour instead if the usual pink. With the standard svga_s3 setting, it will be pink.

Jo22 wrote on 2024-04-02, 18:23:

No no, I don't think it's a false memory.

Massively informative post, thank you.
I haven't tried any of the more accurate emulation avenues yet, but I did force it into using the low intensity pallette 0 mode by using dosbox-staging and manually swapping out the colours in the cfg:
Change the line:
cga_colors = default

to:
cga_colors = #000000 #0000aa #55ffff #00aaaa #ff55ff #aa00aa #ffffff #aaaaaa #555555 #5555ff #55ff55 #00aa00 #ff5555 #aa0000 #ffff55 #aa5500

This is exactly what I remember it looking like when I played it as a kid.

You're welcome. I'm glad you got it working. ^^