The Making Of: The Trap Door

The Trap Door


Expectations for licensed games aimed at children are never high. It’s rare for a developer to engage with their source material beyond taking well-loved and bankable characters and shoving them into a mediocre platformer or, on occasion, a karting game. Even among the honourable exceptions, few children’s titles match the ingenuity and intellectual challenge of 8bit classic The Trap Door. Based on the ’80s claymation TV series of the same name, The Trap Door closely mirrors the show’s format, as Berk the blue-hued manservant attempts to fulfil the culinary demands of the unseen ‘Thing Upstairs’.

Still, players loading up The Trap Door for the first time in 1986 would be more likely to notice the high quality of its visuals than its idiosyncratic design. It’s easy to raise eyebrows now at reviews asking readers if they can “tell the difference between [The Trap Door] and an animated cartoon,” but, in its day, The Trap Door was a supremely clever game whose ingenious engineering enabled some striking art design.

The Trap Door’s creator was Don Priestley, who in 1979, aged 39, left behind a career in teaching in order to pursue a path in programming. “I’d had enough of teaching reluctant, maladjusted teenage boys and decided to drop out rather than burn out,” he recalls. “Computers were then a hot subject, with Maggie Thatcher boasting about ‘one in every school’. I asked my son, who was about 13, whether his grammar school had one.

“They had, but it was kept locked away in the sixth form maths department. I decided to enrol us both in a night school programming course.” As strange as it may seem today, the course did not provide any actual computers to experiment with, but instead a theoretical introduction to the Pascal language. “We could write programs on coding sheets which the teacher took to Lancaster University to turn into punched cards which went into a mainframe,” explains Priestley. “Next week we each received a few sheets of error messages.”

The Trap Door developer Don Priestley.

Despite these limitations, Priestley persevered and later bought a Sinclair ZX81 computer in kit form with £80 worth of unemployment benefits. Soon he was writing hybrid programs in BASIC and machine code, eventually selling ZX81 game Mazogs to Bug Byte for £1,000. Most of his subsequent Spectrum titles were published by Dk’tronics, a living-room outfit run by Dave Heelas that specialised in Spectrum add-ons. “One day he rang me to say that he’d thrown in his lot with some ‘businessmen’ who would give him proper premises, staff, accounting and management for a slice of the action. I was offered the job of software director at £24,000 a year, unlimited expenses and a big shiny new company car,” says Priestley. “I had a long think about this – about five seconds.”

It was at this point that Priestley began his long association with licensed products, then as now an easy marketing hook for any new title. “Dk’tronics managed to get the Popeye licence from King Features, Inc,” says Priestley. There were conditions, however: “The nice man from KFI said that Popeye was to look the part, with a proper sailor suit, tattoo on arm, corncob pipe and facial expressions.” Priestley achieved this, and the result was his first ‘supersprite’. “It was just impossible to make it smaller,” he explains, “KFI were delighted with the first offering of Popeye, with no background, swaggering across the screen.”

Not only were the gigantic sprites unlike what gamers had come to expect, but Popeye (and later The Trap Door) also featured another technical feat long thought impossible on ZX Spectrum hardware: a complete lack of colour clash. Colour clash was caused by the limitations of the display memory in a number of 8bit computers, resulting in a maximum of only two colours per 8×8-pixel cell, often creating ugly results. Priestley’s workaround partly involved the scale of his sprites, which could fill whole cells without causing the character to appear overly blocky, but was also the result of a large amount of time-consuming and tedious work, with the author using up reams of graph paper while working out complex data tables to account for every colour-clashing eventuality. “Although it was complicated and time consuming, it worked, and became my trademark for many games thereafter,” he explains.

Although Priestley was responsible for many of Dk’tronics’ biggest hits, he was made redundant after just two years. “The computer games bubble was bursting, games software houses were going to the wall, and I was unemployed,” he recalls. Now working freelance, Priestley was approached by book publisher Macmillan, which in 1986 was attempting to break into the videogame market with its Piranha label. “I thought then that their timing was, well, crap, but understandably kept mum about it,” he says.

Piranha had acquired the licence for the as-yet-unaired Trap Door TV series, and asked Priestley to design a game around it. The TV series’ large claymation characters were clearly a perfect match for Priestley’s supersprite technology, which had been improved in the intervening years in order to run at a more nimble pace (“I think Popeye ran at about four frames a second!”). But while the supersprite graphics may have improved, they were still tedious to implement and harder still to shoehorn into the Spectrum’s tiny memory. “It may be a surprise to know that I wasn’t a very good programmer,” admits Priestley. “I often used teenage whizzkids to take a piece of my code, which worked OK, and make it smaller and faster. This they could do even though the product was still basically all mine.” But while Priestley was able to ensure that The Trap Door looked the part, what was less clear was how the show, which had little to no action element, would translate into a game.

As in the TV series, Berk is tasked with making a series of gruesome dishes for his master, the unseen Thing Upstairs. The castle Berk and his master share is represented as a world of just six screens. Each is filled with various tools or creatures, all of which can be interacted with whether they’re relevant to the current recipe or not. In order to collect the living, monstrous ingredients Berk’s master would so often demand, players would have to open the eponymous trap door and release the beasties within. “As all the ingredients had to be found and prepared within a relatively small game area I came up with the idea of hiding them or making them difficult to collect,” says Priestley. “So, with a bit of head scratching, I managed to get Berk to pick things up, put them in containers, put containers in containers, and either carry the containers or push them along,” he explains. “What really made any task tricky was that all the ingredients, containers and trapdoor monsters were all available all the time, so if you were asked to make Eyeball Squash and Boiled Slimies you could end up with Boiled Eyeballs and Squashed Slimies!”

Indeed, the freedom to experiment which The Trap Door offered was almost unparalleled. “[Berk] had to be inquisitive, experimental and persistent, which were the characteristics I wanted to engender in the player,” states Priestley. There were concerns, however, that such freeform design might alienate players used to a more linear experience. “At some stage I thought, ‘God, nobody’s going to be able to finish this’,” Priestley explains, “so I introduced Boni the skull to make some helpful comments.” The presence of Boni, a disembodied skull residing in an alcove by the trap door, not only made for a less oblique experience, but also brought the design of the game closer towards fully replicating the concept of the TV series, in which Boni would (for the most part) act in a similarly helpful capacity.

Although it wasn’t enough to sustain Piranha for long, The Trap Door was a hit, both critically and commercially, though Priestley feels there was little in the way of genuinely constructive criticism for any of his games. “I didn’t get much feedback except for magazine reviews based on a fairly cursory look at the graphics, sound and any technical innovations,” he complains. “I really don’t know, for example, how many players got through all the levels of Jumbly, one of my most accomplished programs but horribly difficult and confusing for many.”

Nonetheless, the success of The Trap Door was enough to secure a sequel, entitled Through The Trap Door, now generally less well regarded than its predecessor. “I had free rein to do anything I pleased, so I sent Berk and Drutt on a linear adventure to find dear old Boni,” Priestly explains. The resulting game, which saw players switching between control of Berk and leaping yellow spider Drutt, still has plenty of logic puzzles alongside its larger action element, but despite being bigger the game world feels more restrictive and less open to experimentation.

It wasn’t the last supersprite game though: Priestley went on to create the Spitting Image-inspired royal footman sim Flunky and the surreal Gregory Loses his Clock. Priestley recalls the latter as home to one of his major innovations: “I developed a method of making hundreds of similar but not identical screens of background graphics, each generated from just a two-byte number.”

Still, none of Priestley’s later works, as well-received as they were, would turn their significant technical achievements to the task of bringing to life a world as fully formed as that of The Trap Door. His game could never hope – with or without colour clash – to look just like the TV series it was based on, but it did, in what today would still be an unusual step for a licenced product, reflect the show’s principles and concepts in its own design. Modern games may look like cartoons, but it’s rare that they feel like them.