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If you have the Exercise Files that came with this lesson, I'm going to go back to my Comp panel, Close All, and then open up comp 03-Interpolation where I've already created a couple mask shapes for you. If you don't have the Exercise Files just sit back and watch. This is a fairly easy concept. Here I have a black solid where I've already created two different mask shapes at different keyframes. This first shape of a maple leaf and this second shape of an oak leaf, cool! Now since that keyframing going on, you would just assume this is going to interpolate between those two shapes, but look what happens when I RAM Preview.
I press 0 on the numeric keypad. This leaf is turning in on itself. It's not at all animating the way I expected. What's going on? That's because After Effects really cares about the order that you draw mask points. It looks at the first point you draw for one shape and tries to interpolate that to the first point you drew for another shape. If those points don't line up, then you're going to get the weird inversions like this animation you just saw.
So ideally, when you have two very different mask shapes, you need to pay attention to where the first vertex point is so After Effects has a clue of how it's supposed to interpolate. So how do you figure that out? Well the first vertex point is the first point you drew when you drew the mask. You'll see it later as the point that has two rings around it rather than just a simple dot. So you see my maple leaf shape. It's down here at the bottom. That has the two rings. When I go to my oak shape, it's up here at the top.
That's the point with two rings around it. Ideally, you want these to be in the same location. So let's try a couple of different ideas. I'm going to start off by keeping this one at the bottom of the stem, go to my other point, and pick the bottom left point in that stem. Then I can either use Layer > Mask and Shape Path > Set First Vertex and now you see it has the two rings around it, or merely right-click on that point and I'll get these similar menu item.
Mask and Shape Path > Set First Vertex. Now let's see how that interpolates. That's fairly good. The stems staying correct, but since I have a different number of mask points, the maple leaf and oak leaf, it's not so good. Well you know you don't have to stick with one interpolation. You can try different first vertex points. In general, points at the very bottom, very top, or other identifiable marks and objects are good points to try.
So on this oak leaf, I'll select this top point. Right-click, Set First Vertex, I am going to type the shortcut J to go back to previous keyframe, select this first point, right-click, Set First Vertex. Let's see how that works. That holds the top shape better. The sides don't interpolate quite as well. So if you like, you can continue to try different ideas, such as making this point first vertex, K to jump to later keyframe, Set First Vertex.
That looks a little bit more natural. Using that point right off the base of the stem worked out pretty well. And if necessary you can play games with adding and subtracting points so you have similar vertex or mask points counts in either side to get a smoother interpolation. Well indeed, if you can pay attention to the Info panel you can get some clues. Here's my maple leaf. I'll select that first vertex. I see that there is 41 vertices on the maple leaf shape. I'll press K to jump to the next keyframe. Select that first vertex. 46 points on the oak leaf.
So the oak leaf has more points than the maple leaf. Let's see how this is interpolating. I see the maple leaf's top is crawling along the right side of the oak leaf. So it's a little bit unbalanced, like maybe there are not enough vertices on the right side of the maple leaf. Let's go ahead and hold down the G key when I've got the Selection tool active, and we just add a couple of points here and see how that goes. Oh, we're getting better. Let me add one more point. G, plus symbol, add.
Now I have a much better interpolation in-between those two different mask shapes. I'll press 0 to RAM Preview and now I've got a fairly good interpolation and I can play other games if I want to. There is a more advanced tool in After Effects called Smart Mask Interpolation where we can brute force masks to interpolate from one to another. I'll show that off on a sidebar at the very end of this lesson. But the main thing I want to show you was first vertex point. Very important in animating between two disparate shapes.
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