Appillionaires: Secrets from Developers Who Struck It Rich on the App Store

Chapter 6: Doodle Jump

In the summer of 1991, Croatia was at war. The Republic of Serbia in the former Yugoslavia had invaded the newly declared state. In the shadow of the Croatian War of Independence, two young brothers from Croatia — Igor and Marko Pusenjak — were crouched in the glow of their ZX Spectrum 48k. Pixels blazed late into the night as the two children imagined the possibilities for a game they were designing. Igor took a pencil and a notepad, sketching out character designs and levels, while Marco experimented with the capabilities of the Spectrum. The brothers taught themselves BASIC — a simplified programming language designed to help first-timers learn their way around a computer — but Marko alone would go on to learn Assembler, a notoriously difficult low-level programming language — a delicate, precise way to tell the computer what to do quickly. Only the bravest programmers go near it.

The brothers’ game design used Tom and Jerry as characters. It was based on an entertainment format already established on the ZX Spectrum — similar to the games that the brothers liked at the time — a combination of arcade and adventure. In Igor and Marko’s sketches for the game, the player would guide a character. The character would have to find an object, pick it up, and then work out how the object could be used to progress the storyline. In one episode that Marko recalls, the player would find a key to open a door. Behind the door they’d find a chest. Inside the chest ...