For this tutorial I will be using a free stock image of a pizza to show the use of mask layers.

Using mask layers

Step 1

Open a new flash document.
Import your object onto the stage by selecting file > import > import to stage then select your file and click ok.
If you don’t want to import an object, you can create an object on the stage at this point.

Step 2

Using the selection tool (V) select your object and convert your object into a symbol by selecting F8.
Give your object an appropriate name, check movie clip and click ok.

Step 3

On the timeline insert a new layer called “mask”. This layer will contain your masked object.
On stage create your mask object I use a circle shape but your can use a rectangle shape if you wish.
Convert your mask object into a symbol by selecting F8.
Give your object an appropriate name, check movie clip and click ok.

**As you can see that my mask object is on the pizza itself. You can put your mask object anywhere on the stage because when the mask layer is applied the mask object will not be seen. Also the mask object does not have to be a small size. You can make your mask object as large as you want, just make sure it doesn’t fully cover your movie clip object on the stage.

Step 4

On the timeline insert a key frame (F6) at frame 30 on the mask layer and then insert a frame (F5) at frame 30 on layer 1.

Using the selection tool (v) select the 30th frame on the mask layer. Then drag your mask object so it fills your entire movie clip object, like below:

Step 5

On the timeline insert a motion tween on the mask layer in between the 1st and 30th frame.

Right click on the layer name “mask” and select Mask from the drop down menu. Your timeline should look like below:

Step 6

Test your movie clip Ctrl + enter. You should now have a mask layer.

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