Con­ver­sion Kings: Dou­ble Dragon 3: The Rosetta Stone

The ZX Spec­trum was home to a num­ber of ar­cade con­ver­sions. But how were these large games squeezed into such a small ma­chine? We speak to graph­ics afi­cionado Shaun Mcclure about work­ing with coder Tom Prosser to take on the third in­car­na­tion of the fight

Retro Gamer - - CONTENTS - Words by Paul Davies

Shaun Mcclure on the chal­lenges of con­vert­ing the Tech­nos brawler to the hum­ble Spec­trum in our brand new se­ries

The job of con­vert­ing an ar­cade game to a home com­puter could seem a lit­tle daunt­ing to a coder – es­pe­cially when asked to fit it into 48K or 128K of mem­ory. Hav­ing worked on other con­ver­sions for the ZX Spec­trum, such as NARC, Saint Dragon and Rod­land; how did Shaun Mcclure start the work on Dou­ble Dragon III?

“We man­aged to get a video of an en­tire playthrough of the game,” he ex­plains. ‘We also had two or three ar­cade ma­chines in the of­fices, too. One of these had the Dou­ble Dragon III board in­stalled so we could play it for free. This helped us get a feel for the game and de­cide how to take it on. We were also given the ac­tual game graph­ics to work from, which was very rare.”

The first thing Shaun looked to do was con­vert graph­ics that were cre­ated for the Amiga ver­sion to the Spec­trum. He ex­plains, “First of all, we had to al­ter the ar­cade graph­ics for the Amiga, re­size them and then take them down to 16 colours. We lit­er­ally cre­ated a 16-colour palette with the Amiga pro­gram Deluxe Paint, with ar­eas of the palette re­served for cloth­ing colours, etc. Once we had that, we used its remap func­tion to con­vert the newly re­sized ar­cade im­ages to the new palette. After some touch-up work, I got to work on the Spec­trum ver­sion. The graph­ics needed to be smaller than the Amiga as the Spec­trum screen was smaller, so I had to work out the new size and rescale again, over­draw­ing the graph­ics in black and white.”

Go­ing into specifics, Shaun ex­plains, “The Amiga ver­sion had sev­eral dif­fer­ent bad guys to beat up, a lot of them were iden­ti­cal but wore dif­fer­ent-coloured cloth­ing. To save space in mem­ory, the dif­fer­ent-coloured shirts were cut and over­laid over the sprites to make them look a bit dif­fer­ent.” With less mem­ory to work with than the Amiga, some tricks were per­formed to get the game run­ning well. “For the Spec­trum,

I had de­cided to make the leg and torso an­i­ma­tions sep­a­rate – this meant that we weren’t stor­ing the full bod­ies for things like punch­ing and so on, so the legs didn’t change. We also had to fit them into char­ac­ter bound­aries, this meant that the odd punch had to have shorter arms. We also had to off­set some of the torso frames which were an­other side-ef­fect of hav­ing the tor­sos sep­a­rate and the char­ac­ter bound­ary squash­ing up.”

De­spite this work­around, there were still prob­lems with mem­ory, so cuts to an­i­ma­tion frames were made with Shaun re­call­ing that “ev­ery se­cond or third an­i­ma­tion frame” be­ing re­moved. The orig­i­nal sprites of Jimmy and Billy had eight an­i­ma­tion frames each – this had to be taken down to four, though the an­i­ma­tion still looked smooth enough that both Shaun and Tom were happy with it.

With the main pro­tag­o­nists con­verted, the en­e­mies and bosses were next to be tack­led. This would turn out to be an­other is­sue to iron out, with even more frames for the chop this time. “The en­emy bosses, such as the large mummy at the end of the game, had to be re­ally butchered – de­spite the game be­ing 128K-only.” Shaun ex­plains. “Once again, we cut the legs and tor­sos into two sets of an­i­ma­tions, cut the num­ber of frames but this time we got rid of two out of three frames, and it looked jerky as a re­sult. But be­cause it was a mummy, ba­si­cally we thought, ‘Sod it – it’s a mummy! Mum­mies don’t walk smoothly any­way!’ So we left it as it was.” Some en­e­mies suf­fered an even worse fate and had to be omit­ted in their en­tirety, no­tably the en­e­mies on horse­back you find on level four on the ar­cade game.

Char­ac­ter sprites aside, next to be worked on were the lev­els. The ar­cade orig­i­nal had five large lev­els with mul­ti­ple sec­tions, so a lot of work had to be done to make them look good on the Spec­trum. Com­pro­mises had to be made to fit these in, and to try and keep each level as close to the orig­i­nal as pos­si­ble. “We had the lev­els as blocks, but we had prob­lems con­vert­ing them so we ended up draw­ing them from scratch,” Shaun says. “We kept them based on the ar­cade lev­els, though be­cause a lot of these lev­els weren’t flat – be­ing lots of per­spec­tive at the ends of each level – it was tricky.”

Shaun con­tin­ues, “Tom [Prosser] wanted to ‘rerotate’ the blocks in mem­ory, too. This is where, on scrolling games, we would have a ver­sion of all of the map graph­ics al­ready scrolled, this meant the pro­ces­sor didn’t have to spend time cal­cu­lat­ing this in real time, which would re­ally slow the game down. The down­side to this method is that the blocks scroll into each other, so the more

vari­a­tions in blocks of dif­fer­ing types that you have next to each other, the more it has a knock-on ef­fect on the pre­scrolled blocks that had to be cal­cu­lated. We re­ally had to sim­plify some of the map ar­eas be­cause of this, although you re­ally can’t tell.”

Hav­ing been con­verted by just two peo­ple, a good re­la­tion­ship would have been key to get­ting the right re­sult. The duo was given roughly four months to com­plete the con­ver­sion so how did Shaun find it work­ing with Tom? “Tom was pretty cool,” he replies. “It’s not of­ten that artists get any say about game­play, but I was the one mak­ing a lot of the de­ci­sions about en­emy AI, sug­gest­ing how the mummy should move, that kind of thing. Usu­ally artists get told to ‘go away’ but Tom was re­ally re­cep­tive.”

It seems Tom was also re­cep­tive when it came to Shaun adding a lit­tle hu­mour to the game. The more ea­gle-eyed player may well have no­ticed ‘Tom is a git’ spray-painted along the wall some­where on the first level and also, as Shaun re­mem­bers, “I added lit­tle touches like light switches and plug sock­ets in­side the pyra­mid of the Egypt level.” The scoundrel.

With all the hard work that was put into get­ting such a big game onto the Spec­trum, Shaun is very happy with the fi­nal re­sult. “I think the game­play worked re­ally well, con­sid­er­ing we had a rel­a­tively short time to com­plete it, which was a good feel­ing as we put a lot of work into it,” he con­cludes.

» [ZX Spec­trum] The team had ac­cess to a playthrough video and the game’s graph­ics.

» [ZX Spec­trum] Legs and tor­sos an­i­ma­tions were sep­a­rated.

» [ZX Spec­trum] “I swear I heard a mo­to­bike around here some­where…”

» [ZX Spec­trum] “Oh, what big eyes you have… and teeth. Gulp.”

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