The 2D physics prototype behind GTA’s vehicles

In August 1996, a programmer wrote a 2D physics simulation that would later form the foundation of the vehicle system in the widely popular video game Grand Theft Auto (GTA). Starting as a wireframe demo created in GFA BASIC for an Atari ST computer, the prototype was eventually rewritten in C for inclusion in the actual game. To commemorate its 30th anniversary, the creator has recreated the simulation in JavaScript, offering a remastered version with touch controls for mobile devices.

The game features three vehicle modes: Car, Spaceship (also known as Ship), and Brick. Players can choose their preferred mode through the Settings menu or by pressing specific keys on the keyboard. Collision barriers surrounding the playfield can be enabled or disabled using the 'B' key, while vertical gravity can be toggled with the 'G' key, adding a unique twist to the Ship and Brick modes.

The interface allows for camera controls via the 'Z' and 'X' keys. 'Z' adjusts the camera's 'dead zone,' determining how far a vehicle can move before the camera follows, while 'X' controls a zoom feature that pulls the camera back as speed increases, mirroring the gameplay experience found in GTA.

At its core, the simulation relies on a classical 2D rigid body dynamics system. This approach, while not common at the time, provided a more coherent method of handling rotation compared to the basic high-school 'point physics' (F = ma) employed by most game vehicles. By incorporating proper rigid-body physics, including torques, the simulation offered a more realistic representation of vehicle behavior.

Building upon this core, the programmer introduced a novel vehicle simulation layer based on an approximate model of tire behavior. Although this method was not physically accurate, it proved sufficient for the game's requirements at the time. The recreated JavaScript version allows players to interact with this simulation through intuitive controls, providing a glimpse into the early development of GTA's vehicle system.