Animating the Stroke effect

In the previous movie we copied the paths from Illustrator and applied them to the same layer in After Effects, and they appear as masks. The next step is to apply the Stroke effect. You will find that under Effect > Generate > Stroke. The default settings applies a white color stroke with a 2-pixel border, and it only applies it to the first path that it sees. Now we would like to apply the stroke to all of these paths and animate them sequentially. So make sure you toggle on All Masks, and let's select a different color-- something we can see, like a bright red.

That should make this Stroke Effect easier to see. You can also toggle off Mask Visibility if you'd like to see the layer more clearly. So let's review what the Stroke effect is actually doing. It's rendering a stroke using the masks, and it's placing the stroke on top of the original layer. If you reduce your Brush Size, you can see that the black stroke is underneath. But the Stroke Effect allows you to regenerate that stroke using whatever color you want, whatever width, and it also allows you to animate it.

So one thing we will need to do is to get rid of the underlying pixels, and you do that by changing the Paint Style from On Original Image to On Transparent. Now the original black pixels disappear, but when I increase the Brush Size I only see the line that the Stroke effect is generating. So we will set the Size to 2 for now, and let's look at how to animate it. There are two parameters that you can animate, Start and End. So go ahead and scrub those just so you can see how they work.

You will notice the Start will wipe off the stroke, and it would also wipe it on if I go from 100 back to 0, but it wipes it on counter-clockwise. If we scrub the End parameter from 100 to 0, it wipes off the strokes, and if I go from 0 to 100, it wipes on the circle clockwise and then the little tick marks. So that looks like what I like to do. So let's turn on the Stopwatch for End, set our first keyframe to 0. Notice I'm at time 0, so let's move a few seconds in, maybe a couple of seconds.

And we will set the End parameter to 100%. When I RAM Preview, there is my animation. So let's do that again with the outer ring. We will select it, select Edit > Edit Original, and that will open Illustrator and then we will select all the art that's on that layer. Now we can copy, Edit > Copy. We'll jump back to After Effects, Command+Tab. The outer ring layer is still selected.

Edit > Paste, and that will paste the masks. I will press M so you can see them. But we don't need to make any changes unless you want to reorder them. The only mask I need to check is that the first mask is the circle. So we will Toggle On our Visibility, and let's see which one this is. Yeah, that looks like it's the circle. So we will twirl that up. Since we have already set up the Stroke effect, you can just copy it either from the timeline or from the Effect Controls panel.

Press Edit > Copy, select the outer ring, and Edit > Paste. That should give us exactly the same animation. And you can see I made a classic mistake. I didn't check where the current time marker was when I pasted those keyframes. Fortunately, this is easy to fix. I will press Home, click on the word End to select both keyframes, and when I drag them back I will add the Shift key and they will just snap to the beginning of the comp. So right now we're just getting the basics down.

What you might call the bones of the animation. Once we nest this in the main composition, you can revisit this animation, change the speed, maybe stagger them on, and so on. In the next movie, we will add some color to the outer ring.