Sometimes a target object changes shape so dramatically that using the same shape on it, no longer makes sense. A solution is to crate an altogether new shape, but the key is to smoothly blend the transition between the two. So here is the case we would be looking at now. You can follow along using the replace shape Mocha Script in the Project Media folder. Let's zoom in a little bit. If we look at this hand, from this frame here it has a one shape, but the other end of the clip it has an entirely different shape.
Trying to transition between those two extremes would be too difficult. So what we will do is, we will start at this point, create this shape, here are my control points, you see lots of control points and then at the other end of the clip, we will transition to this shape, which has a completely different set of control points. For this shape, we would start at the end of the clip and roto backwards, for the other shape we would start where we were and roto forward.
Now we need to meet in the middle. I'll select that. As you can see the problem with the first shape is when we start here, start to roto forward, see all those control points, well, now we get a much simpler outline and all the control points bunch up. It becomes difficult to get a smooth, clean line. So we need to switch to a new shape that has far fewer points. So I have added a third transitional shape here and it has far fewer control points.
You can see here there are very few control points on this side, if we go back to the other shape, lots of control points on this side. So this shape is much more appropriate for the target than either of the two extremes. Deselect over here and now you can see the sequence. This is shape 2. we would roto this one backwards, go to the transition shape and then go to the first shape, which we had roto forwards. I will set an end point here so you can see all three shapes transitioning back and forth.
Okay, let's see what the rendered map would look like, I have already done the render and I rendered it to disk with the Motion Blur turned on. So let's take a look at that. Here we are. So this is what all three shapes look like with Motion Blur and transition and everything enabled. We will return back to our clip, and close with this. When switching between two shapes, if the transition frames are a bad fit, then consider adding a third transitional shape.
It may actually be less work than struggling with two inappropriate shapes.
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