Working with Movie Clips and Buttons > Using actions and methods to control movie clips > Using movie clips as masks |  |

Using movie clips as masks

You can use a movie clip as a mask to create a hole through which the contents of another movie clip are visible. The mask movie clip plays all the frames in its Timeline, just like a regular movie clip. You can make the mask movie clip draggable, animate it along a motion guide, use separate shapes within a single mask, or resize a mask dynamically. You can also use ActionScript to turn a mask on and off while a movie plays.

You cannot use a mask to mask another mask. You cannot set the `_alpha` property of a mask movie clip. Only fills are used in a movie clip that is used as a mask; strokes are ignored.

To create a mask:

1 | On the Stage, choose a movie clip to be masked.
2 | In the Property inspector, enter an instance name for the movie clip, such as `image`.
3 | Create a movie clip to be a mask. Give it an instance name in the Property inspector, such as `mask`.
4 | Select frame 1 in the Timeline.
5 | Choose Window > Actions to open the Actions panel if it isn't already open.
6 | In the Actions toolbox (at the left of the panel), click the Objects category, the Movie category, the MovieClip category, and the Methods category, and double-click `setMask`.
7 | In the parameters area, enter the instance name of the mask movie clip.
| The code should look like this:
    image.setMask(mask);

For detailed information, see `MovieClip.setMask` in the ActionScript Dictionary.