A rule that is harder to keep than to write

When I announced the Megadrive version, I set myself a rule: don't port the game, improve it. That sentence is easy to write. Keeping it means asking the same question at every step, and often turning down the easiest answer.

The easiest answer is to rebuild the Atari version line for line. The game works, so why not just copy it? Because the Megadrive is not an Atari, and forcing it to behave like one would mean paying for the Atari's limits without getting anything the Megadrive is good at. So every piece of code gets judged twice: is it faithful to the game, and is it the best this console can deliver?

Here is where that leads.

Handling the characters

On the Atari, every character you see on screen is redrawn by the machine, frame after frame. When a fight gets busy, with two heroes, several enemies, their rocks in the air and an explosion, it is a constant balancing act. I spent more time on it over the last few days, so that the Atari version keeps its pace when things get busy, especially during attacks with several enemies on screen.

The Megadrive was built for exactly this. It displays its characters on top of the scenery by itself: I tell it where to put them, and it takes care of the rest. For the player, the difference shows in the brawls. A crowded scene doesn't make the machine break a sweat, and it leaves me room to fill the screen.

The same artwork, only richer

On the Atari, the scenery, the heroes, the monsters and the effects all share the same sixteen colours. Every shade is fought over, and sometimes you have to choose between the moss on a rock and the flame of a lantern.

On the Megadrive, each family gets its own palette: one for the scenery, one for the heroes, one for the monsters, one for flames and explosions. The scenery no longer has to give up its colours to anyone, and neither do the characters. It is the same artwork, but it shines on the Megadrive.

Halo mode, with a level set at night

This part has one particular quirk: it is ready. The engine can already handle the halo of light that lights up a level plunged into darkness. The level itself, though, isn't ready yet...

The third level will take place at night. You will only see what the lantern lights. Around the hero, the light doesn't stop dead: it fades in rings, and monsters moving away from the glow darken step by step before vanishing into the dark. With two players, each one carries their own lighting, and the two glows merge when the heroes move closer together.

I first tried a simpler method. The result moved in little squares, and the light looked more like a mosaic than a flame. I threw that method in the bin. The one I kept follows the light pixel by pixel, and the console does most of the work.

The details nobody notices, but that will make the difference

There are quieter things too. The dialogue box slides in and out of the screen smoothly, without a jolt. The companion who walks with the hero when you play alone is here as well, and a second player can take control of it at any moment. The title screen, the intro, the first two levels, the plague spreading and the outbreaks budding: everything the Atari version does is on the Megadrive cartridge.

What is still missing

Music. The Megadrive has a sound all of its own, and I have no wish to paste the Atari's sound onto it: that would be the exact opposite of the rule.

And, of course, the third level, the one at night. Both are moving at the same pace as the rest of the game, on all three machines at once.