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Masks

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A mask is a bezier path on a layer that gates the layer’s alpha. Use one to show part of a layer and hide the rest.

A mask on a layer, gating its alpha.
A mask on a layer, gating its alpha.
  1. Select the layer.
  2. Pick a shape tool or the pen tool.
  3. Draw in the Viewer.

With no layer selected, the same tools make a shape layer.

PropertyWhat it does
PathThe bezier path. Drag its points in the Viewer, and keyframe it to animate the shape.
FeatherSoftens the edge, half the width either side of the path.
Point n featherThat point’s own soft-edge width, once the mask has been given a feather per point.
ExpansionGrows or shrinks the mask from its path.
OpacityAdjusts similar to a layer’s opacity property.
ModeHow this mask interacts with the layer and other masks.
InvertedSwaps inside for outside.

A layer can carry several masks, and they combine top to bottom by their mode. Add is the default. Subtract cuts this shape out of what the masks above it built, Intersect keeps where both overlap, and Difference keeps areas only one covers. Lighten keeps the greater of this mask and what the masks above it let through, and Darken the lesser. Setting a mask to None leaves the path drawn and editable while affecting nothing.

One edge of a mask can be sharp and another soft. Right-click the mask’s row in the Timeline and pick Feather per point: every point of the shape gets a Point n feather row of its own, starting at the width the mask already had. The width runs smoothly from one point to the next. One feather width on the same menu drops the rows and goes back to a single width.