GTA Developer Recreates Original Driving Model for Series’ 30th Anniversary

Players can now test different versions of a physics simulation created many years ago.

A former programmer for the original Grand Theft Auto recently revisited the iconic game and shared details about its internal workings.

Patrick Kerr wrote the 2D physics simulation over a weekend in late August 1996. This exact simulation later became the foundation for the vehicle system in Grand Theft Auto:

It all started with a small wireframe demo written in GFA BASIC on my home Atari ST computer. It was later ported to C for use directly in the game. For the 30th anniversary of this development, I recreated it in JavaScript in a slightly prettier, remastered form so that anyone can look at it or play with it.

The simulation offers players several modes: a “car” (1), a technically simpler “spaceship” or “ship” (2), and a “brick” (3). Users can also set boundaries at the edges of the playfield or make it seamless.

Image source: patkerr website

Patrick explains that the simulation initially resembled the brick mode featured in this browser version. He then introduced several improvements, resulting in the ship mode that players can see today. This version of the physics was intentionally designed to resemble the classic 1986 game Thrust.

After that, Patrick implemented the elements needed to make the simulation resemble the car mode.

The system relies on a simple, classic two-dimensional rigid body dynamics simulation. According to Patrick, this approach was not yet common in games at the time, “although there were notable exceptions. Most game vehicles were modeled using basic school-level point physics.”

By this, the developer refers to the well-known formula F = m * a (Force acting on a body equals mass multiplied by the acceleration the body receives under that force).

Patrick explains that the rotational component was handled using various “rather questionable hacks.” Using full rigid body physics, including torques, allows for more consistent rotation modeling.

In addition, the developer added a vehicle simulation layer on top of the base level based on a “simple, approximate, and technically incorrect” tire behavior model:

Basically, it was a fairly educated guess on my part. Although I understood that it did not fully correspond to real physics, it nevertheless felt “good enough” for my purposes at the time.

The 2D Vehicles driving system prototype from the first Grand Theft Auto can be tested via the following link.

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