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
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.”