Depends how detailed it has to be. Here's a quick and untested try for a dumb conversion assuming you know your way around:

1. Convert all textures to 8bit BMP using the ingame palette. Put all BMP files + TRixx in a folder and run TRixx, select option 3, type a filename and hit ENTER. Place generated PIX pack file in PIXELMAP folder.

2. Place ACT file in ACTORS folder, DAT file in MODELS folder and MAT file in MATERIALS. Maybe SCRN4.MAT too I guess. Skip the 'simple_' files and SHELL for now.

3. Hex edit the MAT file with an Hex Editor (there are good free ones) and append .PIX after each texture filename. Most of the times there seem to be two names: a material entry includes the material name and a little further the filename of the texture it uses. So it's always the second one that has to get .PIX added right after. (Sometimes the material name is different from the texture name, just keep track of your progress. You can check in the hex part that the byte before the texture filename is always 08)

4. Duplicate an existing car TXT file, best to try and pick one from a car that resembles the one you're converting. At least physics-wise. Change the filename in the first line. Change the resource loading to match the PIX MAT DAT and ACT files. Remember to also change the number of files to load for each type (usually gets down to 1 but for DAT and ACT that remain at 3). As you haven't prepared BONNET nor SIMPLE models, just leave the previous ones there, they'll be untextured but the game won't care. (For the DAT files, change the one that doesn't seem to have X at the end nor B or BON, BONNET. For the ACT file you'll want to change the one on the line that starts with 0).
Further down, remove FUNKS if any. Then replace the enormous list of numbers between END OF GROOVES and START OF MECHANICS by this:

// CRUSH DATA
0.700000
0.050000,0.300000
0.050000
0.050000
0.000000
0.000000
0
// CRUSH DATA
0.700000
0.150000,0.400000
0.050000
0.050000
0.000000
0.000000
0
// CRUSH DATA
0.700000
0.050000,0.300000
0.050000
0.050000
0.000000
0.000000
0

Don't touch anything else yet.

5. Hijack an existing car entry in OPPONENT.TXT or create a new entry by duplicating an existing one, make it load the new TXT file. Try to start the game and load the car and start a game but then it crashes, try not to cry, cry a lot.

6. If it works, you can then try and adapt the TXT file to make it match the physics and grooves (if any) of the C2 original. The bounding box might be made for the mins and maxs on each axis of the original bounding box I guess. If it still works, you can invest more time in menu pics etc etc

This should be a quick and dirty way to get a C2 car in C1, I can do it very quickly but this also means I might have forgotten stuff. It's not top notch ofcourse as for example the main model should be placed with the origin in its center but it won't hurt the game anyway.

Wade, upload the ACT DAT MAT TXT PIX C1 files somewhere and I'll check it out

I at least need YOUR txt and mat files...

I just had a quick try with the Semi Mk2 myself and it turns out it hits a material limit. I'll fiddle some more and report to you, I didn't think of that in my instructions.
In your files, TXT file is correct, PIX is empty and MAT untouched.

You must convert the tiff files to BMP files + carma palette, place the first half of the BMP files in a folder named SEMI2A and the other half in a folder named SEMI2B. Place TRixx in each folder and run it, hit 3, then ENTER.

You must edit the MAT file to add .PIX after each texture filename as explained in point 3 of my post up here. (maybe you did it but then didn't include the modified MAT in your zip then)

Then the MAT file must be split in two. This is more difficult to explain. I'm uploading a video I did while converting the Semi MK2 to C1, maybe it'll be enough to show you how it's done. I'll update this post when it's done uploading.

[edit] here it is: https://www.youtube.com/watch?v=pmRiL8BBE-Y Please don't mind my terrible english. I'll delete this video in the upcoming days as I intend to make it again but in french with subtitles.

@Wade: At first glance, that looks like a collision problem between world and car to me. Double-check the bounding box and angular momentum proportions, if necessary make the bbox identical to what I did ingame. Lacking pixies won't create this problem.

About the car being untextured, it can be the pixelmaps or the materials or both. Make sure they are loaded propely in SEMI2.TXT (verify filenames and that both PIX files are loaded in each of the three pixelmap entry. Same with the materials below.
Might as well be that your PIX packs are invalid. Can you successfully convert the textures to the 8bit palette and save them as .BMP files? If you do the same as I do for the first texture in the video then there should be no problem (I automated the rest). You can check your PIX packs with Carmagedit to see if textures are properly packed. If the PIX packs are correct and properly loaded in the TXT file, then it must be the MAT files editing.

Again you can upload your C1 files for me to check and report.

By the way, why are you playing Carmageddon in low resolution?


@QTZ: He had also uploaded the C1 txt file in his previous post, it seemed correct.
I don't remember about the Swamp Rat, I can check. But anyway I'm really surprised that the middle wheels work in C2 without their spinning groove being set with proper coordinates. Maybe the fact the model identifier has .ACT at the end triggers a pivot reset. I don't know.
Also don't remember the pixelmap AND material limit per file for cars, it's within the 30s. Need to split in two to bypass the limit or else the game will crash and moan about insufficient material/pixelmap slots in storage area etc.

Your PIX packs are ok, however you applied the wrong palette to the textures! You need to load the carma_tosh one.
And so I guess the problem comes from the MAT files, could you upload them too?

Getting weird, your MAT files seemed in order to me! Also if Carmagedit displays the pixies properly, then they should appear fine ingame too. Silly hypothesis but is it possible you forgot to replace the PIX packs in the PIXELMAP folder once you fixed the palette?

Could you zip up the SEMI2.ACT,DAT,TXT,MAT and PIX files from your C1 folders and upload it? Try not to miss a single file if possible.

You added an unneeded coordinate between the bounding box and the minimum turning circle radius, delete this line (toward the end):

This is what generated the collision issue.

Secondly you didn't add .pix at the end of the filename, you overwrote the data after the filename. Example:
Original:

What you did:

What had to be done:

Do you see the difference? You probably can switch between ADD and OVERWRITE mode in your hex editor by pressing the INSERT key on your keyboard. Just delete both mat files and try again from the original C2 mat file after splitting it in two. You're almost there!

Did you do add .PIX the way I explained in my previous post? Because that's the problem for the non appearing textures.

Ah sorry I forgot to say that you renamed and changed coords of the wrong GROOVES. You edited RRWHEEL.ACT and RLWHEEL.ACT while you had to edit MRWHEEL.ACT and MLWHEEL.ACT. I guess you can just take a quick peek at the video again to be sure.

The car being too high in the gallery is a side effect of this being a quick conversion. I mention at some point in the video that this isn't the proper way to make a C1 addon as the main component isn't positioned at the origin. Fixing this would be too much hassle for little gain I think (would have to do it in PT2 then recalculate bounding box).

Grid image is set in the main TXT file (above the resource list). Cockpit images and damage indicator are set in the HUD TXT file (DATA\64X48X8\CAR\), you can duplicate the SEMI one again if you want. The game uses the Eagle's by default.

And my mistake thinking you were running in lowres, the window is streched in a way that made me think it was the lowres mode scaled up.

Well I suppose starting your own release thread would be best. And yeah making ZIP/RAR files with the proper folder hierarchy makes it WAY easier for anyone to install the addon.

Don't forget though that you can still complete the project some more with a cockpit and bonnet model!

QTZ: Indeed, splitting actually doesn't help. I was a bit misled as it does help with tracks. It seems like the maximum pixelmap files possible to load in the 'resource area' is 40. SEMIBON=10 pixies, so SEMI2 must have 30 pixies max. It looks like the materials have the same limit of 40. Honestly it is a reasonable limit per C1 car.
But as C2 cars use a ton of small pixies, it becomes problematic when doing straight conversions. A solution would be to at least make a bonnet model out of the complex model. This way the bonnet and complex model would share the same material and pixelmap libraries.
Or trying to cut into materials/pixies like the engine and interior, and you'd make the windows black or something instead. Material entries would have to be removed manually from the MAT file.

Haven't had a look at the Swamp Rat yet.

@Yuri/Wade: you should also try to convert the textures without diffusion while applying the palette. Some look better without diffusion and some with it.