Car files

Stunts cars are made of four different resource files: st*.p3s, stda*.pvs, stdb*.pvs and car*.res ; where the * stands for an arbitrary 4-letter abbreviation shared by files of the same car. All of the car graphics are stored in the .p3s and .pvs files. The car*.res, which is the one of most concern when creating a tuned car, contains numerical and text parameters, including data about car performance.

Graphics files (.p3s/.pvs)

Different aspects of a car's appearance are stored in each of the graphic files:

• st*.p3s - 3d shape resource file that stores the graphical 3D models of the car, including their colour data.
• stda*.p3s - Bitmap resource file that contains the dashboard image, including the shifting stick's base. (Movement of tachometer, speedometer and steering wheel dot is controlled by car*.res parameters.)
• stdb*.p3s - Bitmap resource file that contains the shifting knob. For the Corvette, it also stores the digital speedometer graphics.

Each of the files contain a number of independent resources, used on different places or in-game situations. Here a rundown of those resources contained within each file will be presented. For an explanation of internal structure of the resources, applicable to all files here discussed, check the Resource file format article.

3D shapes (st*.p3s)

Standard st*.p3s files contain seven 3D shape resources, each being used in different circumstances:

• car0 shape is the one used in the car selection screen. It is richly detailed for Stunts usual standards, and has pretty high internal resolution.
• car1 shape corresponds to the car actually rendered on-track. Its resolution is much smaller than the car0 shape, the scaling down factor being in the order of 1:20, thus explaining why many fine details seen on the "showroom" car are not seen on-track.
• car2 shape is the very long distance model, used only for the initial zoom-in animation that precedes the "Fasten your seatbelt!" message at the start of a race. It has very low resolution, to the point of being barely recognizable.
• exp0, exp1, exp2 and exp3 aren't really proper 3D shapes, but rather individual lines and polygons that make up the bits of debris seen after a crash.

Dashboard base/static parts (stda*.p3s)

The base elements of the dashboard are actually made of a number of separate bitmaps, not all of them necessarily present in all of the dashboards:

• !cg0 and !eg0 are alternative palettes for non-VGA graphic modes.
• dash is the base bitmap of the dashboard, covering most of its drawn area.
• dast complements the top of the dash bitmap with curved areas, as seen on the Indy for instance. Since all bitmap resources correspond, naturally, to rectangular areas, there's an additional bitmap, dasm which acts as an alpha mask in order to have the correct curved effect.
• roof is the strip seen atop above the windshield for a number of cars - for instance, the ones containing "PORSCHE" or "JAGUAR" inscriptions on the IMSA cars.

Editing and combining car graphics

Graphic files of different cars can be mixed freely when constructing a new car (note that the car*.res may require adjustment so that the indicators work properly on a new dashboard). As for modification of the graphics themselves, until recently that was deemed impossible, for the lack of information about the format employed by the developers to compress the vector graphics. This first major obstacle, however, has been sorted out. (see Tools section below)

Car behaviour (car*.res)

All adjustable aspects of a car behaviour are stored in car*.res. Those include both physics data, such as power curves, and visual parameters, like car height in cockpit view or speedometer behaviour. Also, the file also contains the text data displayed at the car selection screen. Data in car*.res may be read and modified by any hex editor, or more conveniently by a specially-designed graphical editor (see the Tools section ahead).

The function of a large fraction of car*.res hex addreses was elucidated over the years, allowing modifications of many car aspects. Here is a quick reference for those addresses, adapted from the chart available at Lukas Loehrer's site. A more throughout discussion on the effects and quirks of the parameters is available at Car parameters; clicking on a parameter description will lead to the corresponding entry there.

Byte offset	Function
26h	Number of gears
28h-29h	Car mass
2Ah-2Bh	Braking effectiveness
2Ch-2Dh	Idle rpm
2Eh-2Fh	Downshift rpm (auto transm.)
30h-31h	Upshift rpm (auto transm.)
32h-33h	Maximum rpm
37h-41h	Gear ratios (odd offsets)
46h-5Ch	Shifting knob positions (even offsets)
5Dh-5Eh	Aerodynamic resistance
60h-C7h	Torque curve
CAh-CBh	Grip
F6h-F7h	Car height on cockpit view
110h-14Dh	Steering wheel dot movement
14Eh-223h	Speedometer needle movement
150h-159h	Digital speedometer
224h-32Dh	Rev meter needle movement
32Eh-EOF	Text data (car selection screen and high score table)

Version compatibility

Cars that use graphic files from Stunts 1.0 do not work properly on 1.1 versions, and vice-versa. Doing so causes a crash in the car selection screen. Although the car*.res files may be exchanged between versions, car performance won't be the same due to the known differences between game versions in that respect.

Tools

The car*.res files can be read and edited by any hex-editor or text editor able to display files in hexadecimal mode - HT and Vim are examples of each case). A more convenient alternative are graphical hex-editors designed especially for Stunts car hacking. Mark Nailwood's Car Blaster, by far the most used of those, has resources such as tags on useful bytes and comparison between cars. Other editors include Caredit and Winedit.

Modified cars are not recognized in the RPL Info tool, also created by Mark Nailwood.

In 2008, dstien created a tool named stunpack to unpack some files of the game. His project is registered here [1] and is still under development, but it looks really promising. the day when we will be able to change car shapes is approaching.

See also

• Car parameters
  
• Car model physics
  
• Cheated cars