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Did a little bit further investigation:

In memory, once the dashboard files are unpacked, STDA (Acura) seems to contain these chunks.

dash
gbox
inm1
inm3
ins1
ins2
ins3
roof
whl1
whl2
whl3

(Notably there's no !CGA and !EGA chunks or anything similar, which makes sense - the Amiga version only supports a single graphics mode of 4 bitplanes / 16 colors)


STDB for the Acura is a little more curious:

!pal
dot
dot1
dot2
dota
gnab
gnob

All of those are present in the DOS version, except for the !PAL chunk.

This is where things start to get interesting. As I mentioned, the Amiga version is only running in 16 color mode, but when I took a screenshot it counted at least 22 colors.

What they appear to have done is implemented a unique 16 color palette for every dashboard, so even though it is running in 16 color mode it can display up to 32 colors at once, with a universal 16 color palette for the main game display and a custom set of 16 for every dashboard.

The Amiga "copper" co-processor allows you to change colors on the palette on a line, so the programming of the copper in 4D Sports Driving looks something like this:

- Set the colors to the top dashboard
- Wait for the scanline that starts rendering the main game display
- Set the colors to the main game palette
- Wait for the scanline that starts rendering the bottom dashboard
- Set the colors to the bottom dashboard


I think I'm not really going to have time to dig any deeper into it.

---

Another weird thing is - in the place in memory where the file size is supposed to be, instead we've got the ASCII characters "PPkc". When I did a search to find the significance, one of the first results was about Test Drive 2 on Amiga - https://eab.abime.net/showthread.php?p=1379496. I believe this suggests that the files are packed with "rpck" (like the 3D files are) but without the header that the 3D files have.

I'm so sorry I missed all of these messages! I thought I had notifications set on this thread.

I did notice the needles etc didn't line up between the custom dashboard and the Amiga original, but I hadn't even thought of the idea of fixing the dashboard by copying the original Amiga dashboard settings into the RES file. I probably should add that to the utility if we can't solve the dashboard conversion issue.

I'll try to take another look at dashboards in the next few days. From memory, they were compressed in a way that I couldn't immediately recognise, it didn't have a header etc. But I'm assuming that the Amiga version will accept uncompressed dashboards so long as they're in the right format.

What I *might* be able to do is run the game, find the uncompressed dashboard in memory, and then dump that to give some clues as to what format is expected.

Thought this may be of some interest here - I did some experiments converting some of the DOS custom cars to Amiga, details are at English Amiga Board.

I don't know if I'll do any more on the project, I got stuck on the dashboard graphics (which seem to be crunched in a custom format, and presumably are VERY different to the DOS format anyway). But in brief, I discovered:

- The resource files are identical to the DOS format, excepting that the byte order of words and longwords is flipped for the Motorola M68K processor.

- 3D shapes are almost identical (word/longword flipping not withstanding) except that the "reserved" part of the structure can have a value, and vertices are four words instead of three.
 
Having said that - I think they are just junk values, and the additional word of data on vertices is probably just to keep data aligned at multiples of 8.