Shape as Mask

In Autograph, many elements have a Mask slot:

• Each layer contains a Mask to make its Source partially disappear.
• Most Modifiers have a Mask slot to localize their action to a specific area.

This Mask slot uses the Alpha channel of whatever is connected to it. This content may come from a connection to a Reader, a Generator, or from a Link or Share.

Difference with After Effects

In After Effects, a Mask is a specific item that applies only to layers. Referring to an external source as a Mask in After Effects is done using a Track Matte or a Set Matte effect, whereas in Autograph, a Mask is more generic and can be connected to any source.

We'll see that this approach offers a wide range of possibilities, such as using all of the Shapes Generator's features in a Mask slot.

Drawing a Layer Mask using the Shapes Generator

In this chapter, we'll use the Shapes Generator to create Paths and Styles, which output images with an Alpha channel. The result of this Generator can then be used as a Mask.

Remember that the current selection in the Selection Overview will define which item the Path creation tools will act on.

To draw a Mask on a layer, one solution is to:

• Select the layer in the Timeline
• Click on its Mask line in the Selection Overview
• Switch to the Draw Bézier Curve tool
• Start drawing in the Viewer

Later, we'll look at an even faster way of drawing a Mask.

A Shapes Generator will appear on the Mask line, containing:

• A Path Group
• A Path
• A Fill Style

This is exactly the same structure we've described so far.

Automatic Switch to Mask Mode on Layer Selection

Drawing a Mask on a layer is a very common task, especially in Rotoscopy. That's why after selecting a layer, the Path creation tools will automatically switch to Make Mask on the Layer mode.

This option is accessible from the top bar of the Viewer:

The two creation modes are:

• Create a new Shape Layer: active by default when no layer is selected
• Draw a new Path on the Mask: active by default when a layer is selected

This method is faster than the one described above, as it doesn't require you to select the Mask line in the Selection Overview.

The previous method, on the other hand, is more generic and allows you to precisely define where you want to add the Shapes Generator. This is especially useful for drawing a Mask on a Modifier.

Drawing a Mask on a Modifier

Most Modifiers have a Mask slot to localize their action to a specific area.

The generic method we've defined allows you to:

• Add a Blur Modifier to a layer
• Select the Mask line of the Modifier in the Properties section
• Switch to the Draw Bézier Curve tool
• Draw a Mask

The new Shapes Generator and its contents appear in the Selection Overview:

This is also the way to add Masks to the Garbage Matte and Core Matte slots of the Color Difference Key Modifier (similar to the Keylight effect in After Effects).

Advanced Masks Using all Shapes Generator Features

All the Shapes Generator's features can be used in a Mask slot:

• Use animated Stroke Styles rather than simple Fill Styles
• Add any Image Modifier to Styles, Shape Groups or the Mask slot itself
• Add Path Modifiers to Masks
• Use Path Generators rather than manually drawn Paths
• Etc. ...

This makes it possible to create visually complex effects, even though their setup is very straightforward. Simply click on the parameter where you want to add a Shapes Generator, then use the Selection Overview to understand the various interactions between items.