How did SCI render in CGA?

[troflip]

I know it was automatically done by the interpreter/engine, but does anyone know the particular algorithm?

(ScummVM has a "render mode" for this, but it doesn't work)

[edit: ok, easy enough to get working in DOSBox]

[troflip]

After some experimentation, answering myself, it went like this (in case anyone is interested in this esoteric information) for the cyan/magenta form of CGA:

Code: [Select]

black black
navy magenta
green cyan
teal black/cyan
maroon magenta
purple black/magenta
brown white
silver cyan/magenta
grey black
blue cyan
lime cyan
cyan black/cyan
Red magenta
fuchsia black/magenta
yellow white
white white

When colors were dithered, they just took from one of the component colors. This means A/B could look very different than B/A. For example:
yellow/fuchsia    ->  white/black
fuchsia/yellow   -> magenta/white

[MusicallyInspired]

It's worth noting that, at least in Hercules Monochrome's case, different SCI drivers rendered colours differently. Back when I had my first computer that my dad had given me, a 286 with a 40MB HDD and a Hercules Monochrome card/monitor, I tried two different Hercules drivers from different SCI games and discovered this result. I don't know if the same is true for CGA or not. Wouldn't it be the driver files that do this though? Would hacking the driver files themselves provide any answers?

And yes, ScummVM has the same set of options for every game. That doesn't mean they all work for every supported engine. They're left over from when SCUMM was the only supported engine. Sometimes they implement them in other engines (sometimes in not the best ways), but mostly they don't really work in my experience.

[Kawa]

Just tested. KQ4 with its CGA320C driver was uglyballs with the maroon/brown/green palette on navy. Left DOSBox running and switched to CGA320BW, it was teal on navy.

On the other hand, LSL3 with LSL2's CGA drivers? Passable. Attached are CGA320BW, CGA320C, EGA320, and ScummVM renders.

[troflip]

Interesting... navy is mapping to black in this case. So it looks like different color mappings were used for different games...

[Kawa]

For fun I put Larry's CGA drivers in KQ4. Left is KQ4's, middle is Larry's, right is EGA and ScummVM.

[troflip]

Yeah, so it looks like the mapping was defined in the drivers, and was different for different games.

Laura Bow herself looks terrifying with SQ3's CGAC driver (equally so with LSL2's):

[Kawa]

So... you gon' add a CGA simulation mode to SCI Companion?

I remember when I made a Jill of the Jungle sprite editor. You edited the VGA data and there were two smaller EGA and CGA live previews next to it. There was no EGA or CGA data, only mapping info.

[troflip]

Haha, nope :-)

It's for a puzzle for Cascade Quest. Part of the game will have some kind of CGA emulation mode...

[troflip]

Well that's fun...

[OmerMor]

Don't forget Sierra provided CGA drivers for their SCI1-EGA versions.
Here's Space Quest 4 in CGA:


Another interesting display mode is the 8-color used in the PC-98 Japanese SCI0 games: Quest for Glory 1 and Police Quest 2.
I wrote a wiki page on the subject:
http://wiki.scummvm.org/index.php/Quest_for_Glory

[Kawa]

I am suddenly reminded of the plugs in SQ5, which were... understandably done in three different pic resources.

[troflip]

Why did they do that? (Haven't played SQ5... looked at a playthrough and only the VGA resource was used... so... confused)

[Kawa]

You mess with the plugs to fix something. You mess with them just right and you trigger this visual easter egg.

You might notice the CGA version isn't quite.

[MusicallyInspired]

Interestingly, if you're running the game in VGA mode removing the plug makes that screen EGA. If you're running with the EGA640 dithered driver it makes the screen CGA.