SLOW IN & SLOW OUT - The 12 Principles of Animation in Games.

Hello! Welcome to New Frame Plus. Let’s talk about another principle of animation. So far we have talked about Timing, Squash & Stretch and Anticipation. This time, let’s talk about Slow In & Slow Out. Back in animation’s early days, some of the more savvy animators at Disney and other studios observed that character movement felt more “spirited” when it lingered on the key poses; when characters didn’t just move from one to the next at a perfectly linear speed, but slowly accelerated out of one key pose, speedily moving and then decelerating into the next.

And, in addition to feeling more lively, this quality of movement also felt more grounded in how things actually move in real life. Because it takes time for things to speed up and slow down. I mean, your car doesn’t go from 0 to 60 INSTANTLY. Nor does it instantly stop when you hit the brakes.

Which, you know... probably for the best. To show what this looks like in action, let’s bring back our old friend “ball moving across the screen”. Remember back in the episode on Timing when I used this ball to demonstrate the concept of Spacing? Turns out I was giving you a preview of Slow In and Slow Out! Let’s say that the starting position on the left is the ball’s first key pose, and the ending position on the right is another key pose.

If the ball moves from one to the next without any Slow Out or Slow In, then it will just travel from A to B at a constant speed. Which… you know. That’s fine. But this time let’s have it Slow Out of the first pose. You see how it favors that position a little longer as it takes time to accelerate? And now, let’s also add some Slow In as it reaches its destination.

Now the ball is not only accelerating and decelerating , but it’s favoring both the origin point and the destination with its movement, lingering near each location so that you have more time to see it there. And on top of that, the movement itself feels more visually interesting, right? Now the movement across the screen has some more zip and energy.

It’s a bit more “spirited”. But, for a more practical example, let’s look at this applied to a character. And it’s easiest to see this principle in action when the effect is exaggerated a bit, so look at this Overwatch emote of Brigitte fixing her shield.

You see how she’s really lingering in each of these poses, almost coming to a complete stop? It makes the Slow Into and Out of each pose all the easier to see. So let’s say these three poses are the key poses she’s hitting. Watch how she moves from one to the next… Acceleration… deceleration… pose.

Slow out… slow in… pose. Even on this little head turn, the rotation of the head Slows Out… ...Slows In. And notice that lingering on these key poses isn’t just helping to effectively demonstrate the weight of her body, it’s also giving those poses greater priority in the performance, emphasizing and drawing attention to those moments.

For a slightly more understated example, consider this shot of Sora, noted sweetheart, not knowing how phones work. Starting on this first pose, slight Slow Out… Slow In… Slow Out.... Slow In. He does enter and leaves certain poses quicker than others, but there is a bit of acceleration and deceleration each time.

Now, this principle may be a bit harder to see happening with more naturalistic movement, since the characters aren’t holding on key poses in a cartoony fashion, but make no mistake: Slow In and Slow Out are still in effect here. All the parts of these characters' bodies are still respecting the physics of acceleration and deceleration.

Whether exaggerated or naturalistic, this principle helps to give our animated objects an appropriate sense of weight, which is crucial to making their movement feel right. One of the easiest ways we can tell that this hammer is heavy is because we can see how much effort it takes to get it moving.

An object which is heavy is going to require a bit more time and energy to get moving than an object which is lightweight. Which is not to say that a big heavy object can’t move at high speed, of course; it just might need a little more time or power to accelerate to that speed.

But, there are some times when you specifically DON’T want to use Slow In or Slow Out! Like, just as an example, maybe the object in question is being impacted by an external force. Consider the momentum of your standard video game hedgehog. When he’s just moving under his own power, it takes Sonic here quite a bit of time to accelerate from a stop to full speed, and his deceleration isn’t instantaneous either.

But if he hits a solid wall? BAM. That’s gonna stop him pretty fast. Or if he happens to contact a spring? He is instantly off like a shot fired out of a gun. And actually, a gunshot is another great example. The kick of this gun feels so right specifically BECAUSE there is no Slowing Out of that initial pose.

It’s just instant kick. You might also intentionally choose to use less Slow In and Slow Out if you’re animating some sort of machine. Very even, linear movement with harsh stops and starts tends to feel extremely mechanical , so minimizing or even completely eliminating the Slow In and Slow Out from an object’s movement can be a great way to lend it that robotic affect.

You might also intentionally not use Slow In and Out just for comedic effect! Sometimes just having a character SNAP into a pose instantly just feels really funny, no matter how unrealistic it looks. Of course, that’s only going to feel appropriate if you have a heavily exaggerated animation aesthetic.

It would feel completely wrong for Ellie ever move like that for ANY reason, but under the right circumstances? It’s perfect. And when you’re creating animations for a game, there will be times when you have to minimize the Slow In or Slow Out for the sake of game-play.

Players like their controls to feel responsive, which means they need to see quick visual feedback for their inputs. And a realistically weighty Slow In to each move is not going to help with that. That sort of slow acceleration, in this case, is just going to make the character feel sluggish.

So, animators often have to find alternative ways to sell the weight of our player characters. Oh, quick side note: you might sometimes hear this principle referred to as “Ease In and Ease Out”? It’s the same thing; the terms are just used somewhat interchangeably.

Don’t worry about it. At its most fundamental level, Slow In & Slow Out is about respecting the physics of acceleration and deceleration, of force vs inertia. But this principle isn’t JUST about replicating physics. Yes, it does help to sell weight, but it’s also a tool for animated appeal.

For emphasizing your key poses. Whether you are applying it in a highly exaggerated fashion or more naturalistically, Slow In and Slow Out will make your animation feel more… well, “spirited”. And that’s four principles down! If you would like to see the videos about the rest of them, be sure to subscribe and hit that bell and whatnot.