Apple Motion 4 - Manual (Page 1099)

To convert control points from corners to curves and vice versa
Do one of the following:
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Command-click a curved point to turn it into a corner (Linear) point.
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Command-drag a corner point to turn it into a curved (Bezier) point, creating adjustable
tangent handles.
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Control-click one or more selected points, then choose Linear or Smooth from the shortcut
menu to change the control point type.
Curved Bezier control points have two tangent handles that you use to adjust the curvature
of the shape on either side of the control point. These handles can be adjusted in a variety
of ways to create symmetrical and asymmetrical curves. By default, these tangent handles
are locked to one another at an angle of 180 degrees, although this can be overridden
to allow each tangent to be independently adjusted.
Important: If Record (automatic keyframing) is turned on, turning a corner into a curve
causes an animated effect in which the corner gradually turns into the curve.
To adjust a Bezier curve using the control point’s tangent handles
Do one of the following:
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Drag a tangent handle to adjust its length. By default, the opposing tangent is locked to
180 degrees, and adjusting the angle of one tangent automatically adjusts the other.
However, the length of each tangent can be independently adjusted.
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Option-drag either tangent to break the relationship between opposing tangents. Once
this relationship is broken, adjustments to one tangent have no effect on the other, and
both tangents can be rotated freely.
1099 Chapter 17 Using Shapes, Masks, and Paint Strokes