Sonic Retro’s Physics Guide

tl;dr: The description of the physics and implementation details of the 16-bit Sonic the Hedgehog games hosted at Sonic Retro is complete and amazing.

This is one going out to all you developers out there, either current or aspiring.

It’s amazing to me how fussed, nay, obsessed-over the 16-bit Sonic the Hedgehog games are even to this day. There are a lot of good things about them, and arguably the best is their platforming engines, which are among the best in the field. They take advantage of the processing power of the Genesis/Mega Drive, fueled by a Motorola 68000 processor, the same processor as the classic Apple Macintosh, clocked only slightly slower. This was basis of Sega’s infamous “blast processing” slogan at the time, touting how much faster the Genesis was than the Super Nintendo Entertainment System. This was somewhat unfair, as SNES carts often came with supplemental chips in them that acted like co-processors, and was of a completely different architecture as well with different characteristics, but it did make the Sonic engine possible. A lot of the credit also goes to Sonic programmer Yuji Naka, who is legendary in game coding circles for a very good reason.

If this is the kind of discussion that makes your heart race, we’re glad to have you reading Set Side B! If it’s not, that’s okay. I’m a bit stymied myself, even though I love dives like this.
(All images in this post from Sonic Retro.)

The result of the Genesis’s power and Naka’s expertise was a game engine with, yes, raw speed, but also a lot of nuance. If you jump and land on an enemy or monitor, you can control the height of your rebound, no matter how fast you were going when you hit it. If you jump while on a slope, you don’t jump straight up but away from it, which takes some getting used to at first but can be taken advantage of. There’s lots of fun little cases like these, and figuring them out, and their implications, is the source of a lot of the joy of playing Sonic the Hedgehog for the first time.

Those two places where the slope only intrudes slightly into Sonic’s ground tile are what get me.

I’d even argue, without the solid engine, and great level design taking advantage of it, all of Sega of America’s marketing efforts, which formed the foundation of the media juggernaut that Sonic has become today, with several cartoon series and comic books, and two successful movies and a third one in the works, would have been for naught.

Judging by the later 2D adventures, the nuances of Sonic the Hedgehog’s engine are difficult to grasp without a good amount of effort. It is likely that Sega themselves don’t have the institutional memory to understand how they worked, which is why they went to Christian “The Taxman” Whitehead, and others from the fan game community, to make Sonic Mania, which has a faithful recreation of the original games’ physics.

Why has no one made a Sonic half-pipe trick skateboarding game?

Bringing it back around, the obsession of the Sonic fan community has produced a number of disassembles of the game’s code, which have served as the basis for a wide array of romhacks of rather shocking levels of quality. I wrote about many of those in the Someone Set Up Us The Rom ebooks (ahem).

They also served as the basis for the subject of this post, the physics descriptions at Sonic Retro. Here is basically all you need to make a Sonic-style platformer. Synthesizing this and putting it into practice is a formidable task on its own, but it’s a doable one, and you don’t have to read source code (other than your own) to do it. To those who attempt this task, we salute you! And let us know how it goes!

Sonic Retro: Physics Guide

Baba Is You XTREME

By now many of you are no doubt familiar with Alvi Tekari’s Baba Is You (itch.io, Steam, Switch, Android, iOS). The premise is simple. In a Sokoban-style world composed of discrete blocks aligned with a grid, you try to get a figure (usually the sheep Baba) to a goal (usually a flag). But nearly everything about this game world is malleable, according to special word blocks in each level. If a set of three blocks is arranged in a horizontal (reading left to right) or vertical (reading top to bottom) line, then that statement becomes true throughout the level. In fact, every level comes with certain statements already in effect: it is only because somewhere it says BABA IS YOU that you can control Baba, and if something else IS YOU, then you can move it too. And you can make new rules by moving the words to make new sentences.

Baba Is You became an indie darling from its game jam release in 2017, and in 2019 it absolutely exploded, being featured on several game stores including Nintendo’s eShop picks page. Its rules are simple, yet their implications becoming diabolically complex later on. Not to give away some absolutely amazing secrets, but there are very few games that get as hilariously weird as Baba Is You-or as difficult. Baba Is You is a challenge that will keep you going for weeks, but eventually pays it all off with one of the best end game sequences anywhere. If you haven’t played it yet, you really should. I did a Q&A with Alvi Tekari for Game Developer about the creation of Baba Is You, and I think it’s one of the best interviews we’ve done.

This is all to make sure we’re on the same page when I mention the sublimely ridiculous Baba Is You XTREME, a free parody of Baba Is You made by Baba Is You‘s own creator!

Baba Is You XTREME seems just like the original at first, right until you press the first key and discover: the game now has a completely spurious physics engine! Baba no longer snaps a step at a time centered in the cells of a Sokoban grid, but now moves around freely, with acceleration and friction. The same is true with all the other objects on the screen that are IS PUSH. Objects that ARE STOP are locked in place, though.

Rules like SKULL IS DEFEAT might seem insurmountable, until you turn to the power of ROCK

The addition of physics makes the execution of any move into a challenge to itself. The rule system is still in place, some old words have much weirder implications, and there are even some new words to explore. There’s only 11 levels (it is a free game, after all), but around level seven you’ll be scratching your head. But one implication of the physics is that words that are in a corner aren’t completely impossible to shift like they were in a grid setting, so with some dedicated pushing it’s possible to break some troublesome sentences here that would be impossible in Baba Is You‘s Cartesian cosmos.

This physics make this a much trickier puzzle than it would be in Baba Is You

It’s completely free, so if you’re a fan of BIY it’s worth checking out. And if you haven’t tried Baba Is You yet, it is worth a look too!

Baba Is You XTREME (itch.io, Windows)