Flash CS5: The Missing Manual

Spotlight Effect Using Mask Layers

Imagine placing a sheet of red construction paper containing a cutout of a starover a piece of green construction paper. The result you see, when you look at the two sheets stacked on top of each other, is a green star on a red background. That's the concept behind mask layers, a special type of layer that lets you create shaped "portholes" through which an underlying (masked) layer appears.

At a masquerade ball, masks hide the important stuff—your face. It's a little different in Flash and other graphic arts endeavors. Masks hide part of a picture in order to reveal the important stuff—the subject. You use masks to direct the eye of your audience. And when you apply a classic tween to the porthole, you can create an effect that looks like a spotlight playing over an image—mighty cool, indeed.

Here's how you go about it:

1. Open the file 04-3_Mask_Layer.fla.

   You can download this file, a working example of the file (04-4_Mask_Layer_done.fla), and all the other examples shown in this chapter from the Missing CD page at www.missingmanuals.com/cds.

2. Click Layer 1 to select it.

   In the example file for this section (04-3_Mask_Layer.fla), Layer 1 contains a bitmap image.

3. Click the Insert Layer button. (The Insert Layer button is on the bar below the layer names and looks like a folded-over page.)

   Flash creates a new layer named Layer 2 and places it above Layer 1.

4. Double-click the layer icon next to Layer 2.

   The Layer Properties window appears (Figure 4-24).

   Figure 4-24. Use ...