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Hi there, in this tutorial we're going to look at Masking. We're going to cut a hole in our doughnut. Hey, we've already done that before with the big circle. But this time, look it's an actual hole in there, not just a red circle that matches the background. So let's go and learn how to do that in After Effects.
To get started, go to 'Exercise files', open up '08 Masking'. There's one called 'Pie Chart Image Mask', open it up. And I've just made this really basic, a pie chart, like we did before. But it's got that secret trick where it looks like a doughnut, really, it's just a regular old pie chart with a colored circle in the middle, so I'm going to undo that, put it back. We need to do it the proper way. Why? Because if I turn off my background it's actually just a red dot. So you might have a video in the background, or some images all moving across the screen in front of other objects, lots of reasons.
So what I want to do is, we need to keep it. So I'm going to rename mine, I'm going to call it my 'Mask'. And what I'd like to do is, we're going to use something called a Track Matte. What that means is we're going to use this layer to mask the layers underneath it. Now the problem is, the Track Matte can only do the one directly underneath. So I can't mask this one as well. I couldn't mask the Layer above it either. It has to be wherever your Mask is, so I'm going to use this as my Mask. It has to be directly underneath.
So, to get around that, I can either have two of these masks, and do these two separately, or I can just select these, and group them by Pre-Composing. So right click 'Pre-Compose', and I call this my 'Pie Chart'. Now this Mask Layer can mask this Pie Chart underneath. To do it, select 'Pie Chart' and you might be on 'Switches', toggle this button here. So you can see Track Mattes, and say, I'd like to track this first one here, 'Track Matte Mask'. It's doing the opposite of what I want but there's an option in there, that says 'Alpha Inverted'. It's going to play, looks exactly the same as what it was before, except now, when I turn that background layer off, it's an actual hole. If I need to go in and edit this Pie Chart here now all I got to do is double click here, or up here where I called it Pie Chart. Double click, go inside. These are my two layers, I can make my adjustments and play around with it.
When I'm finished, go back to my simple Pie Chart. We're back to where we were before. Nice little hole. Turn that back on. So that is masking one on one, just using a Track Matte. Just make sure it's directly above the Layer you want to mask, and if you want to mask lots of layers, group them together using Pre-Compose. All right, let's get into some more masking.