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5. Animating grass

Finally, let's bring our parabolic arc to life!

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Video transcript

- So far we've talked about how to create a blade of grass using a parabolic arc and a width parameter. We refer to this kind of geometry creation here at Pixar as Modeling. We've also talked about how to create a color, and we refer to that as Shading. Next we're going to talk about something even more exciting, that is Animation, how to make the blade of grass move. Notice in this shot how the grass is moving gently indicating a gentle breeze. We call this kind of subtle motion Keep Alive because if there was no motion at all it would appear stale or dead. But we don't want so much motion that it draws attention away from where the director wants you to be looking. So how are we going to animate each blade? Well to animate, I just need to know where each control point is in each frame of the animation. So, I can just record the motion as I move them around. So here's a simple little animation, and that's probably enough frames right there. And now I can replay that animation as many times as I like. In this case, I'm just cycling back and forth through the animation. So, this is how this one blade looks when animated, and here's how that motion looks when it's copied out to a bunch of blades of grass. Starts to give you a feeling for how a field of grass might move. But in this case, all the blades of grass are moving exactly the same which isn't very realistic, but we can add a little bit of variation by having each blade start the animation at a slightly different time, and that's what I can control with this slider here. So, I can add just a little bit of variation, or I can add a lot of variation. And now it's starting to look a lot more realistic. That's one way to add variation, but another way to add variation is using randomness. In fact, we use randomness so often and in so many different ways that we're going to devote an entire tutorial to it. But for now, use this interactive to see if you can animate two different shots. One with just a little bit of gentle Keep Alive like on a calm day, and another that looks like a very windy or stormy day.