Masking

Masking Basics

Masking is a feature with which you can selectively block areas of a layer. You can use masking to hide objects under a mask, animate the mask or object under the mask, or even place multiple masks in a scene. This can serve to accomplish effects such as “illuminating spotlight” or “magnifying glass”. Basically, the mask acts as a window that reveals the area of layers that lie beneath it -only under the shape you draw on a mask layer will other items in linked layers be visible. The rest of the mask layer conceals everything. A mask layer can contain only one mask item. You cannot have a mask layer inside a button, and you cannot apply a mask to another mask.

Masking example

On the picture to your right, you can see a Giotto stage with an imported bitmap. Note the white circle in the middle. This circle acts as a hole to what will be seen in your animation. Circle is on the Mask layer, and bitmap is on the Masked layer (see below). The result should be like in the picture below.
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As you can see only the surface under the object from the Mask layer is reviled in the final result. Of course you can animate objects in Mask layer so that they expand, shrink, change form…

How to use masking

Mask layer

For masking to work you need to create a mask layer. This layer is different by its characteristics from normal layers and guiding layers. A mask layer contains shape(s) that blocks, or masks, objects from one or more layers to which it is linked. This means that you can link more than one layer to the mask layer. Linked layers become masked layers. To create a mask layer right-click on the appropriate layer and select Mask from the context menu. You will see an icon appear left of the name of the layer that tells you that this is now a guiding layer. You can now draw a mask. Using appropriate tools (Brush, Rectangle and Oval Tool) you can draw desired object to serve as a mask. Everything in your animation that passes or appears under the area of drawn objects in mask layer will be visible. Everything else will be hidden or masked.
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Masked layer

Each mask layer must have one or more masked layers where the objects that fall under the mask effect will be stored. To designate one layer as a masked layer just right-click on the layer and select Masked from the context menu. Notice how the icon appeared next to the layer’s name. For masking to work properly Masked layers must always be under the appropriate mask layer.
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Removing mask

You can remove the mask by right-clicking on the mask layer and unchecking the Mask option in the context menu, or by deleting the whole layer. Removing the mask will automatically remove Masked option for masked layers underneath it.