How Sackboy Learned to Love Physics

Image for article titled How Sackboy Learned to Love Physics

Last night, Media Molecule's David Smith accepted four awards for LittleBigPlanet at the Game Developers Choice Awards. I'm amazed he's awake enough to lecture on the game's physics this morning.


Here are some key insights Smith had into the challenges of making a game where physics is everything and logic is next to nothing:

"I think what a lot of people mean when we talk about physics in games [is that] it's more complex, emergent phenomena… that we're trying to use in LittleBigPlanet. You can make things seemingly more complex than the sums of its parts."

You need good physics in a game, Smith said, because "it helps you to suspend your disbelief in the world around you."

It's not enough to just have ragdoll physics. Smith says that "developers feel you can somehow get something for nothing" by going this route, but they're actually making their game suck by not taking into account all the things that can go wrong with ragdoll deaths.

In LittleBigPlanet, the challenge of physics was all about letting things go wrong — within a certain stretch of reason. Having the world be 2D instead of completely 3D allowed Media Molecule's physics engine to handle a certain amount of chaos without creating an environment where everything could lead to a crash.

"If you really need to have all that strong control of what the player's doing," said Smith. "You probably shouldn't be using physics."


Beyond that, it was all about finding out what the Sackboys could and couldn't do. This was a lot harder than just letting the characters run around in the environment because the development team found that there was a conflict of interest between what people knew they could do in real life and what they thought they could get away with in the game.

"You don't really think people can change direction in mid-air, do you?" Smith asked the audience.


I was about to raise my hand, but he changed slides to talk about how things like "air control" (where, yes, Mario can jump several times his own height and change direction mid-jump) and other video game expectations got in the way of LittleBigPlanet's physics engine — particularly when level designers bought into the expectations.

"A level designer's expectation is that a jump will take you to the same height no matter where you do it," Smith said. "So you have this situation that's kind of unpalatable to level designers [like] flipper objects that — if you jump when that flipper is turning — [propel you] very high into the air."


Smith says he got around that particular snag by programming the Sackboys' legs to bend when they hit the flipper — like you'd do in real life to absorb the impact of something coming at your feet really fast.

"Shit happens," said Smith said, rounding out the talk. "More games should consider embracing the chaos of physics. There are problems, but they can be creative opportunities."


And it's this kind of thinking that rakes in the statuettes. Take note, kids.



But you can change direction mid jump! Gravity sees to that. I mean, otherwhise we'd all be floating off in space by now.