Hello, welcome to this lesson on After Effects. In this lesson, we will learn how to enable expressions in After Effects. When a motion graphic artists first hears the word expressions, they may think of lines of complex code and some complex programming language. Fortunately, that's not true, and expressions are not scary as they sound. In fact, some expressions in After Effects can be created without typing a single line of code. For example, let's add a new shape layer. We'll select a star shape and draw a star in a view panel. I'll also add a new null object layer by selecting layer, new, null object. I'll name this layer, follow me. Next, I'll the position a null to the left side of the view panel and create a position key frame. Then I'll scrubbed to the end of the timeline and move the null all the way over to the right. To make the star shape follow the null layer, I can just drag a pick whip from the shape layer to the null layer and will follow along. However, if I add rotation to the null layer, that will affect the star as well. What if we just wanted to affect a position and have the star be placed at the exact location of the null and move with it? First, we will unparent the star layer by selecting none in the link menu. Next, select the shape layer and press P for position. Also make sure position's visible in the null layer. Now we will pick whip from the position to position, I'll tap the space bar, and see, the star moves across with the null exactly into position in null. Now, if I try to rotate the null layer, it has no effect on the star. And you've actually created your first expression. To see the expression, twirl up into positions value under shape layer, and you see an expression has been written out created by After Effects when we did the pick whip. If you click the expression language menu icon, you will get a list of built-in expressions in After Effects that you can select from, or build your own expressions. To remove an expression, just press the Alt key and click on the stopwatch icon. Let's reset the top layer to the center, and try another way to enable expressions and cover several popular expressions. First, I'll send her to pivot point of our shape by selecting layer, transform, center anchor point in layer content. The first expression we'll explore is called wiggle, and we'll change the value with a given frequency. Press the S key to adjust scaling. Now hold down the Alt key and click the stopwatch. Notice there's an expression entry for this parameter. So I clicked in timeline where it says transform scale, and now we can start typing WYG, and a wiggle expression comes up in our selection list. So I'm going to click to select it, We tried to play back this animation, nothing happens because the wiggle needs two values in order to work properly. We also get an error message when I click on a wiggle expression, so we need to enter two values, the first value is the frequency, I'll try number one, the second value is the amount of wiggle or the amplitude, I'll try 100. playing back, you can see how the star shape is changing over time. If we were to manually key frame this animation, it would take a lot of key frames. Plus the advantage of an expression, it'll continue to run as long as the animation is running, even if you change the time of your animation. Once again, we can remove an expression by holding the Alt key and clicking the stopwatch. This time let's hit the R key and adjust rotation. I'll click Alt and the stopwatch, this brings up my expressions, this time, I'm gonna type in the word time, which is another popular expression. If I were to play back, there's no effect, because the default value of time is one. We need to do is multiply time by a number. I'll try to number 20, and this will affect the rotation. I add a number, the faster rotation will happen over time. This is a good expression to use if you're animating something like a wheel. I will once again, hold the Alt key down and click the stopwatch to remove the expression, I'll hit P for position. I will explore one more expression, this is a very popular one, and it's the random expression. I'll hold Alt, click the position stopwatch, I'll click where the expressions are in the timeline, now type in the word random. For random to work properly, you need to enter two values separated by a comma, the first value is a low value and the second is the highest value, and this case, I'll type in zero and 1000. I'll scrub and play back, and I still have a problem, my star is still not moving. The reason for that is position has an X and Y value, and we only have one expression, so after a fact does not know whether we want to change the position of X or Y. To fix this, right click the word position and choose separate dimensions. Now we have X and Y separated, I can all click the exposition stopwatch. Once again, type in random, enter my two values of zero and 1000, scrub the first frame, hit the space bar, and now we get a random placement of our star between zero and 1000, and it changes on every frame. In the next lesson, we're going to learn how to add a slider to control expressions in After Effects. Thanks for watching.
