Nabiki

**Flapping**, also called **nabiki** (なびき), applies to any cloth, hair, or other light object which flaps when in the wind or being pulled along. Sometimes the term extends to effects animation, like waves on the shore looping. The process for creating this flapping motion is shared pretty closely across all types of flapping material, with minor variations.

Flapping motions don't actually behave quite like the other repetition effects we've looked at. Flaps are a type of effect animation. Rather than actually animating something moving, we're animating the visible results of invisible forces. A flag doesn't get an urge to do the worm and start wiggling. Air lifts it. A skirt doesn't flare when a character starts running because it's excited, it drags because of inertia and air resistance. It feels better to get you used to moving something we can actually see before talking about animating the result of motion we can't see–in a way, this is secondary motion.

That being said, basic flapping motion is fairly simple, all things considered. It's a nice change of pace from the somewhat more complex topics, so let's get into it.

First of all, let's look at what you'll get from those pesky layout artists. Like with most repetitive motion, it's usually just going to be two frames – the start and the end. Flaps usually have even spacing.

A flap like this is made up of three keys and two inbetweens, the middle keyframe is omitted just like in a lip flap in most cases, though you might sometimes get an inbetween guide. Usually, it's expected that you will be able to complete everything from just the two keys.

With a shot like this, you're technically dealing with gousei – the poll never moves, and you don't want to re-trace it every time. Remember to separate the pole, and be careful about overlaps as you work on the moving section.

The key to animating a flap like this is wave motion. It's almost like there's an army of invisible rolling pins moving underneath the cloth of the flag at a steady rate. Your job is to track those pins as they move under the cloth, creating a wave.

## Finding The Middle For All Frames

Like usual, you're going to start this process by finding the middle drawing. We need to space our two keys 50% apart, then use this to find the new positions of our peaks and troughs. I like to think about this as following one rolling pin as it travels under the fabric of the flag, lifting it.

Once we move over A1, we use the distance between it and A2 to find out the halfway point. That gives us the proper trace of A3!

## Rinse and Repeat

Once the trace is done, we just move all the drawings back to their original positions.You're going to repeat this process for each frame, using the two drawings on either side of it, finding the halfway point using peaks and troughs, and drawing out the wave as it travels along the flag. It's a pretty straightforward process once you've done it yourself a few times.

Your animation is going to look something like this once all five frames are done. You'll know it's working if you can feel the lifted cloth move forward and across the length of the flag. If anything feels out-of-step, then the cloth will seem to judder irregularly. These problems tend to compound if you make a mistake in one frame, so flip through regularly.

One small but important detail to note is the crease line on the inside of the flag. Exactly how wide and thin this gets is going to be up to you. The important thing to remember is that it should look consistent and believable compared to the rest of the animation. Adjust it as needed!

This basic flapping motion is can go beyond cloth and hair. It's also how you get smoke, fire, and water effects, so remember it well! We'll be using it a lot more when we dive into effects animation. For now, just keep in mind that a surprising number of things move with this same wave pattern, and we can use it to make lots of beautiful effects.