Reversing Grand Prix Circuit

[HerrNove]

Has anyone ever analyzed Grand Prix Circuit? It's an earlier product of DSI and some routines were clearly taken from it. It contains .PCS (CGA) and .PES (EGA) resource files that are compressed the same way as Stunts.

Once extracted, the resource files can be open with Stressed, but the format has differences. E.g. Stressed is unable to detect the asset format, and even after manually choosing "Bitmap", the resulting image has wrong colors and seems 3x or 4x compressed horizontally. The image in the screenshot should be Monza GP's map: it is still recognizable but clearly some further processing is needed.

[HerrNove]

This is how the map appears in the game.

[alanrotoi]

niiiiiiiiice!!

[HerrNove]

Happy to report a partial success. We can now read most (EDIT: all) of Grand Prix Circuit's EGA assets!



And the changes also allow to read the handful of Stunts' EGA resources, including the editor's icons.



There are still some glitches (EDIT: now fixed ) but LLM-based development has its plus sides :-)

@dstien @llm

[HerrNove]

My mod is coming out quite well :-)

The title is set: "Don Matrelli's Legacy"

Pity I could not figure out how to change the sky color. (EDIT: ah, just found out how to put a background going up to the top)

[Cas]

Really cool!

[alanrotoi]

Wow congrats! It looks great! I think you can edit Grand Prix Cycles (1989) as well, since they are very similar games.

[HerrNove]

Wow congrats! It looks great! I think you can edit Grand Prix Cycles (1989) as well, since they are very similar games.

Yes it works! Turns out the format of The Cycles is an intermediate evolution step between GPC and Stunts, but easily added. Also, thanks to your hint I found out that someone has already built a vehicle engine editor for these earlier DSI titles, and a guy was investigating the music format. The DSI ecosystem is getting quite big 🎉

https://github.com/albertus82/cyclesmod

[HerrNove]

Good news: the whole engine parameters for GPC have already been documented, thanks to the guys behind the cyclesmod project (an equivalent sort of CarWorks for earlier DSI games).

Discovery of the day: the power curves displayed in the car showroom are only vaguely related to the values that the game really uses. In particular, the McLaren receives an artificial boost around 9500 rpm.

[KyLiE]

In particular, the McLaren receives an artificial boost around 9500 rpm.

That's when the VTEC kicks in.

[HerrNove]

Stressed is now 99% able to load GPC assets. The only mysterious glitch is that some of the bitmaps are loaded with inverted colors, like the Ferrari and McLaren logo (but not the Williams').



Another curiosity: the car selection screens are stored as XOR-difference with respect to the Ferrari one.

[alanrotoi]

It looks messy but as used you can't notice it

Btw, is it possible to edit tracks? I think Grand Prix Circuit and The cycles have some differences here because the second has hills and ramps and GPC is just always flat. Maybe it's not a big difference in the code since in any case they are 2D tracks. Just thinking...

[HerrNove]

Btw, is it possible to edit tracks?

Yes, I figured out the format last month   But the layout is stored in the .exe, not in the datafiles. So for now the only way to build the track is with a text or hex editor.

Here a video with my first circuit (before I add curves): https://www.youtube.com/watch?v=yohwZZDyO-o

Off topic, but I'm happy for Colapinto's good result yesterday

[alanrotoi]

Thanks! Here many people if fan of Colapinto. There is a big audience of the F1 because of him.
I would like to watch it but I'm not attracted to races. I don't know why. The same happens with local racing tournaments like Turismo Carretera (TC) is like DTM but with Camaro, Challenger, Camry, Mustang and Torino. I like the cars, I like the competition... But I always forget to watch it. It's not in my system.

About your video.... It's awesome! I liked the dark part, like it was a night mode! Cool improvement!

[HerrNove]

Another small thing Spanish speakers might appreciate: it took some hours but I managed to hack the font used by GPC. So the name of this driver (son of a famous rally driver nicknamed "El Rey") can be written correctly