Rotobeziers

Rotobeziers

Rotobezier shapes are designed to animate a mask over
time; they’re like Bézier shapes (discussed in Chapter 3)
without the handles, which means less adjustment and
less chance of pinching or loopholes when points get
close together. Rotobeziers aren’t universally
beloved, partly because it’s diffi cult to get them right in one
pass; adjoining vertices change shape as you add points.

Activate the Pen tool (G key) and check the Rotobezier
box in the Tools menu, then click the layer to start drawing
points; beginning with the third point, the segments are,
by default, curved at each vertex.
The literal “key” to success with Rotobeziers is the Alt/
Option key. At any point as you draw the mask, or once
you’ve completed and closed it by clicking on the fi rst
point, hold Alt/Option to toggle the Convert Vertex
tool . Dragging it to the left increases tension, and makes
the vertex a sharp corner, like collapsed Bézier handles.
Drag in the opposite direction, and the curve rounds out.
You can freely add or subtract points as needed by
toggling the Pen tool (G key).
The real advantage of the Rotobezier is that it’s impossible
to kink up a mask as with long overlapping Bézier handles;
other than that, Rotobeziers are essentially what could be
called “automatic” Béziers (Figure 7.4). By drawing enough
Bézier points to keep the handles short, however, you may
fi nd that you don’t need them.